diff --git a/SConstruct b/SConstruct
index a457e7d..cf81332 100644
--- a/SConstruct
+++ b/SConstruct
@@ -1,3 +1,3 @@
 build_dir = ARGUMENTS.get('build_dir', 'build')
-VariantDir(build_dir, 'helianthus', duplicate = 0)
+VariantDir(build_dir, 'src', duplicate = 0)
 SConscript(build_dir + '/SConstruct')
diff --git a/data/sound/beep.ogg b/data/sound/beep.ogg
deleted file mode 100644
index 71f5128..0000000
Binary files a/data/sound/beep.ogg and /dev/null differ
diff --git a/data/sprite/breadball.png b/data/sprite/breadball.png
deleted file mode 100644
index da1cba7..0000000
Binary files a/data/sprite/breadball.png and /dev/null differ
diff --git a/data/sprite/bricks.png b/data/sprite/bricks.png
deleted file mode 100644
index fe10e29..0000000
Binary files a/data/sprite/bricks.png and /dev/null differ
diff --git a/demo/.gitignore b/demo/.gitignore
new file mode 100644
index 0000000..b0bedda
--- /dev/null
+++ b/demo/.gitignore
@@ -0,0 +1,2 @@
+/copy/
+/build/
diff --git a/demo/SConstruct b/demo/SConstruct
new file mode 100644
index 0000000..cf81332
--- /dev/null
+++ b/demo/SConstruct
@@ -0,0 +1,3 @@
+build_dir = ARGUMENTS.get('build_dir', 'build')
+VariantDir(build_dir, 'src', duplicate = 0)
+SConscript(build_dir + '/SConstruct')
diff --git a/demo/data/sound/beep.ogg b/demo/data/sound/beep.ogg
new file mode 100644
index 0000000..71f5128
Binary files /dev/null and b/demo/data/sound/beep.ogg differ
diff --git a/demo/data/sprite/breadball.png b/demo/data/sprite/breadball.png
new file mode 100644
index 0000000..da1cba7
Binary files /dev/null and b/demo/data/sprite/breadball.png differ
diff --git a/demo/data/sprite/bricks.png b/demo/data/sprite/bricks.png
new file mode 100644
index 0000000..fe10e29
Binary files /dev/null and b/demo/data/sprite/bricks.png differ
diff --git a/demo/src/SConstruct b/demo/src/SConstruct
new file mode 100644
index 0000000..19b17e6
--- /dev/null
+++ b/demo/src/SConstruct
@@ -0,0 +1,26 @@
+
+
+import os
+env = Environment()
+env['ENV']['PKG_CONFIG_PATH'] = os.environ.get('PKG_CONFIG_PATH')
+
+
+# config
+
+libs = ['helianthus']
+flags = ' -O0 -g -lm -Wall -fmessage-length=0 '
+
+
+# files
+
+sources = [ 'main.c' ]
+
+
+# build
+
+env.ParseConfig('pkg-config --cflags --libs ' + ' '.join(libs))
+
+env.Program(
+	target = 'demo',
+	source = sources,
+	parse_flags = flags )
diff --git a/demo/src/main.c b/demo/src/main.c
new file mode 100644
index 0000000..06e17a7
--- /dev/null
+++ b/demo/src/main.c
@@ -0,0 +1,47 @@
+
+#include <helianthus.h>
+
+Sprite ball, brick1, brick2;
+Sound beep;
+
+void init() {
+	ball = createSpriteEx(200, 200, 64, 64);
+	spriteSetAnimation(ball, "data/sprite/breadball.png");
+	
+	brick1 = createSpriteEx(200-32, 200+64, 64, 64);
+	spriteSetAnimation(brick1, "data/sprite/bricks.png");
+	spriteSetTintColor(brick1, rgb(0, 0, 1));
+	
+	brick2 = createSpriteEx(200+32, 200+64, 64, 64);
+	spriteSetAnimation(brick2, "data/sprite/bricks.png");
+	spriteSetTintColor(brick2, rgba(1, 0, 1, 0.5));
+	
+	beep = createSound("data/sound/beep.ogg");
+}
+
+void draw() {
+	double dt = worldGetTimeStep();
+	double speed = 100;
+	
+	spritePointTo(ball, mouseX(), mouseY());
+	
+	double x = spriteGetX(ball);
+	double y = spriteGetY(ball);
+	if (keyDown("left"))  spriteSetX(ball, x - speed*dt);
+	if (keyDown("right")) spriteSetX(ball, x + speed*dt);
+	if (keyDown("up"))    spriteSetY(ball, y - speed*dt);
+	if (keyDown("down"))  spriteSetY(ball, y + speed*dt);
+	
+	spriteSetSpeedAndDirection(ball, speed/2, spriteGetRotation(ball));
+	
+	if (mouseWentDown("left")) soundPlay(beep, FALSE);
+	
+	drawSprites();
+}
+
+int main() {
+	worldSetInit(&init);
+	worldSetDraw(&draw);
+	worldRun();
+	return 0;	
+}
diff --git a/dev-build.sh b/dev-build.sh
new file mode 100755
index 0000000..d21ea79
--- /dev/null
+++ b/dev-build.sh
@@ -0,0 +1,7 @@
+#!/bin/bash
+
+set -e
+
+scons PREFIX=$1 install
+cd demo
+scons
diff --git a/helianthus/SConstruct b/helianthus/SConstruct
deleted file mode 100644
index 4bcbc1d..0000000
--- a/helianthus/SConstruct
+++ /dev/null
@@ -1,40 +0,0 @@
-
-env = Environment()
-
-
-# config
-
-libs = ['gtk+-3.0', 'glib-2.0', 'cairo', 'SDL2_mixer']
-
-
-# compute build options
-
-flags = ' -O0 -g -lm -Wall -fmessage-length=0 '
-
-
-# files lists
-
-target = 'helianthus'
-
-sources = [
-	'animation.c',
-	'array.c',
-	'collider.c',
-	'common.c',
-	'drawing.c',
-	'group.c',
-	'test.c',
-	'sound.c',
-	'sprite.c',
-	'world.c',
-	'main.c' ]
-
-
-# build
-
-env.ParseConfig('pkg-config --cflags --libs ' + ' '.join(libs))
-
-env.Program(
-	target = target,
-	source = sources,
-	parse_flags = flags )
diff --git a/helianthus/animation.c b/helianthus/animation.c
deleted file mode 100644
index 068d7c6..0000000
--- a/helianthus/animation.c
+++ /dev/null
@@ -1,76 +0,0 @@
-
-#include <glib.h>
-#include <cairo.h>
-
-#include "private.h"
-
-
-static HeliArray cache;
-
-static cairo_status_t read(void *closure, unsigned char *data, unsigned int length) {
-	return fread(data, length, 1, (FILE*)closure)
-		 ? CAIRO_STATUS_SUCCESS : CAIRO_STATUS_READ_ERROR;
-}
-
-static cairo_surface_t* loadFrame(const char *path) {
-	if (!heliStringEndsWithLowcase(path, ".png"))
-		return NULL;
-	FILE *f = fopen(path, "rb");
-	if (f) {
-		cairo_surface_t *frame = cairo_image_surface_create_from_png_stream(&read, f);
-		fclose(f);
-		if (!frame)
-			fprintf(stderr, "helianthus: cannot load PNG content form file: %s\n", path);
-		return frame;
-	}
-	fprintf(stderr, "helianthus: cannot open image file: %s\n", path);
-	return NULL;
-}
-
-static HeliAnimation* load(const char *path) {
-	HeliAnimation *a = calloc(1, sizeof(*a));
-	a->path = heliStringCopy(path);
-	
-	GDir *dir = g_dir_open(path, 0, NULL);
-	if (dir) {
-		while(TRUE) {
-			const char* name = g_dir_read_name(dir);
-			if (!name) break;
-			char *p = heliStringConcat3(path, "/", name);
-			cairo_surface_t *frame = loadFrame(p);
-			free(p);
-			if (frame) heliArrayInsert(&a->frames, -1, frame, (HeliFreeCallback)&cairo_surface_destroy);
-		}
-	} else {
-		cairo_surface_t *frame = loadFrame(path);
-		if (frame) {
-			heliArrayInsert(&a->frames, -1, frame, (HeliFreeCallback)&cairo_surface_destroy);
-		} else {
-			fprintf(stderr, "helianthus: cannot load animation by path: %s\n", path);
-		}
-	}
-	
-	return a;
-}
-
-static void unload(HeliAnimation *a) {
-	assert(!a->refcount);
-	free(a->path);
-	heliArrayDestroy(&a->frames);
-	free(a);
-}
-
-HeliAnimation *heliCreateAnimation(const char *path) {
-	HeliPair *item = heliStringmapGet(&cache, path);
-	if (!item) item = heliStringmapAdd(&cache, path, load(path), (HeliFreeCallback)&unload);
-	HeliAnimation *a = (HeliAnimation*)item->value;
-	++a->refcount;
-	return a;
-}
-
-void heliAnimationUnref(HeliAnimation *a)
-	{ if (--a->refcount <= 0) heliStringmapRemove(&cache, a->path); }
-
-void heliAnimationFinish()
-	{ heliArrayDestroy(&cache); }
-
diff --git a/helianthus/array.c b/helianthus/array.c
deleted file mode 100644
index d6b56d2..0000000
--- a/helianthus/array.c
+++ /dev/null
@@ -1,133 +0,0 @@
-
-#include "private.h"
-
-
-void heliPairInit(HeliPair *p) {
-	p->key = p->value = NULL;
-	p->freeKey = p->freeValue = NULL;
-}
-
-void heliPairDestroy(HeliPair *p) {
-	if (p->key && p->freeKey) p->freeKey(p->key);
-	if (p->value && p->freeValue) p->freeKey(p->value);
-	heliPairInit(p);
-}
-
-void heliArrayInit(HeliArray *a) {
-	a->items = NULL;
-	a->count = a->allocated = 0;
-}
-
-void heliArrayDestroy(HeliArray *a) {
-	heliArrayClear(a);
-	free(a->items);
-	heliArrayInit(a);
-}
-
-HeliPair* heliArrayGet(HeliArray *a, int i)
-	{ return i >= 0 && i < a->count ? &a->items[i] : NULL; }
-
-void* heliArrayGetKey(HeliArray *a, int i) {
-	HeliPair *item = heliArrayGet(a, i);
-	return item ? item->key : NULL;
-}
-
-void* heliArrayGetValue(HeliArray *a, int i) {
-	HeliPair *item = heliArrayGet(a, i);
-	return item ? item->value : NULL;
-}
-
-HeliPair* heliArrayInsertPair(HeliArray *a, int i, void *k, void *v, HeliFreeCallback fk, HeliFreeCallback fv) {
-	if (i < 0 || i > a->count)
-		i = a->count;
-	if (a->allocated < a->count + 1) {
-		a->allocated += a->allocated/4 + 32;
-		a->items = realloc(a->items, a->allocated*sizeof(a->items[0]));
-		memset(&a->items[a->count], 0, (a->allocated - a->count)*sizeof(a->items[0]));
-	}
-	if (i < a->count) {
-		memmove(&a->items[i+1], &a->items[i], (a->count-i)*sizeof(a->items[0]));
-		memset(&a->items[i], 0, sizeof(a->items[0]));
-	}
-	++a->count;
-	
-	HeliPair *item = &a->items[i];
-	item->key = k;
-	item->value = v;
-	item->freeKey = fk;
-	item->freeValue = fv;
-	return item;
-}
-
-HeliPair* heliArrayInsert(HeliArray *a, int i, void *v, HeliFreeCallback fv)
-	{ return heliArrayInsertPair(a, i, NULL, v, NULL, fv); }
-
-void heliArrayRemove(HeliArray *a, int i) {
-	if (i < 0 || i >= a->count) return;
-	heliPairDestroy(&a->items[i]);
-	memmove(&a->items[i], &a->items[i+1], (a->count-i-1)*sizeof(a->items[0]));
-	--a->count;
-	memset(&a->items[a->count], 0, sizeof(a->items[0]));
-}
-
-void heliArrayClear(HeliArray *a) {
-	while(a->count > 0)
-		heliArrayRemove(a, a->count-1);
-}
-
-HeliPair* heliStringmapFind(HeliArray *a, const char *k, int *gtOrEqIndex) {
-	int i0 = 0;
-	int i1 = a->count - 1;
-	int cmp = i0 < a->count ? strcmp((char*)a->items[i0].key, k) : -1;
-	if (cmp >= 0) {
-		if (gtOrEqIndex) *gtOrEqIndex = i0;
-		return cmp ? NULL : &a->items[i0];
-	}
-	if (i1 > i0) cmp = strcmp((char*)a->items[i1].key, k);
-	if (cmp < 0) {
-		if (gtOrEqIndex) *gtOrEqIndex = a->count;
-		return NULL;
-	}
-	if (cmp == 0) {
-		if (gtOrEqIndex) *gtOrEqIndex = i1;
-		return &a->items[i1];
-	}
-	
-	while(i0 + 1 < i1) {
-		int i = (i0 + i1)/2;
-		cmp = strcmp((char*)a->items[i].key, k);
-		if (cmp == 0) {
-			if (gtOrEqIndex) *gtOrEqIndex = i;
-			return &a->items[i];
-		}
-		if (cmp < 0) i0 = i; else i1 = i;
-	}
-	if (gtOrEqIndex) *gtOrEqIndex = i1;
-	return NULL;
-}
-
-HeliPair* heliStringmapGet(HeliArray *a, const char *k)
-	{ return heliStringmapFind(a, k, NULL); }
-
-HeliPair* heliStringmapAdd(HeliArray *a, const char *k, void *v, HeliFreeCallback fv) {
-	int i;
-	HeliPair *item = heliStringmapFind(a, k, &i);
-	if (item) {
-		if (item->value && item->freeValue) item->freeValue(item->value);
-		item->value = v;
-		item->freeValue = fv;
-	} else {
-		item = heliArrayInsertPair(a, i, heliStringCopy(k), v, &free, fv);
-	}
-	return item;
-}
-
-int heliStringmapRemove(HeliArray *a, const char *k) {
-	int i;
-	if (heliStringmapFind(a, k, &i)) {
-		heliArrayRemove(a, i);
-		return TRUE;
-	}
-	return FALSE;
-}
-
diff --git a/helianthus/collider.c b/helianthus/collider.c
deleted file mode 100644
index 500cc28..0000000
--- a/helianthus/collider.c
+++ /dev/null
@@ -1,27 +0,0 @@
-
-#include "private.h"
-
-int heliCheckCollision(HeliCollider *a, HeliCollider *b, double *normX, double *normY) {
-	// corner with side
-	// corner with circle
-	// circle with circle
-	#warning "TODO: heliCheckCollision: not implemented yet"
-	return FALSE;
-}
-
-int heliPointCollision(HeliCollider *c, double x, double y) {
-	x -= c->x;
-	y -= c->y;
-	if (c->type == COLLIDER_CIRCLE) {
-		return x*x + y*y <= c->radius*c->radius;
-	} else
-	if (c->type == COLLIDER_RECTANGLE) {
-		double a = c->rotation*(PI/180);
-		double sn = sin(a);
-		double cn = cos(a);
-		return fabs(x*cn - y*sn) <= c->width*0.5
-			&& fabs(x*sn + y*cn) <= c->height*0.5;
-	}
-	return FALSE;
-}
-
diff --git a/helianthus/common.c b/helianthus/common.c
deleted file mode 100644
index a46a70f..0000000
--- a/helianthus/common.c
+++ /dev/null
@@ -1,96 +0,0 @@
-
-#include "private.h"
-
-
-cairo_t *heliCairo;
-
-
-static char *colors[] = {
-	"transparent", "0 0 0 0",
-	
-	"black",       "0 0 0 1",
-	"white",       "1 1 1 1",
-	"gray",        "0.5 0.5 0.5 1",
-	
-	"red",         "1 0 0 1",
-	"green"        "0 1 0 1",
-	"blue"         "0 0 1 1",
-	
-	"yellow",      "1 1 0 1",
-	"magenta",     "1 0 1 1",
-	"cyan",        "0 1 1 1",
-
-	"yellow",      "1 1 0 1",
-	"magenta",     "1 0 1 1",
-	"cyan",        "0 1 1 1",
-	
-	"brown",       "0.5 0.5 0 1",
-};
-
-
-int randomNumber(int min, int max)
-	{ return max <= min ? min : rand()%(max - min + 1) + min; }
-
-double randomFloat()
-	{ return (double)rand()/(double)RAND_MAX; }
-
-
-char* heliStringCopy(const char *x) {
-	int len = strlen(x) + 1;
-	char *cp = malloc(len + 1);
-	memcpy(cp, x, len);
-	return cp;
-}
-
-char* heliStringConcat3(const char *a, const char *b, const char *c) {
-	int la = strlen(a);
-	int lb = strlen(b);
-	int lc = strlen(c);
-	char *s = malloc(la + lb + lc + 1);
-	memcpy(s, a, la);
-	memcpy(s + la, b, lb);
-	memcpy(s + la + lb, c, lc);
-	s[la + lb + lc] = 0;
-	return s;
-}
-
-int heliStringEndsWithLowcase(const char *s, const char *tail) {
-	int ls = strlen(s);
-	int lt = strlen(tail);
-	if (lt > ls) return FALSE;
-	for(int i = 0; i < lt; ++i)
-		if (tolower(s[ls - i]) != tolower(tail[lt - i]))
-			return FALSE;
-	return TRUE;
-}
-
-void heliLowercase(char *x)
-	{ while(*x) { *x = tolower(*x); ++x; } }
-
-
-void heliParseColor(const char *x, double *color) {
-	color[0] = color[1] = color[2] = 0;
-	color[3] = 1;
-	
-	if (*x == '#') {
-		++x;
-		int hex[8] = { 0, 0, 0, 0, 0, 0, 15, 15 };
-		for(int i = 0; *x && i < 8; ++i) {
-			char c = tolower(*x);
-			if (c >= '0' && c <= '9') hex[i] = c - '0';
-			if (c >= 'a' && c <= 'f') hex[i] = c - 'a' + 10;
-		}
-		for(int i = 0; i < 4; ++i)
-			color[i] = (hex[i*2]*16 + hex[i*2 + 1])/255.0;
-	} else
-	if (isalpha(*x)) {
-		int count = (int)(sizeof(colors)/sizeof(*colors)/2);
-		for(int i = 0; i < count; ++i)
-			if (strcmp(x, colors[i*2]) == 0)
-				{ heliParseColor(colors[i*2 + 1], color); return; }
-	} else {
-		sscanf(x, "%lf %lf %lf %lf", &color[0], &color[1], &color[2], &color[3]);
-	}
-}
-
-
diff --git a/helianthus/common.h b/helianthus/common.h
deleted file mode 100644
index 1a25cb9..0000000
--- a/helianthus/common.h
+++ /dev/null
@@ -1,22 +0,0 @@
-#ifndef HELI_COMMON_H
-#define HELI_COMMON_H
-
-
-#ifndef TRUE
-#define TRUE  1
-#endif
-
-#ifndef FALSE
-#define FALSE 0
-#endif
-
-#ifndef PI
-#define PI 3.14159265358979323846
-#endif
-
-
-int randomNumber(int min, int max);
-double randomFloat();
-
-
-#endif
diff --git a/helianthus/drawing.c b/helianthus/drawing.c
deleted file mode 100644
index ba5e348..0000000
--- a/helianthus/drawing.c
+++ /dev/null
@@ -1,197 +0,0 @@
-
-#include <cairo.h>
-
-#include "private.h"
-#include "drawing.h"
-
-static double colorBack[4] = {1, 1, 1, 1};
-static double colorFill[4] = {0.5, 0.5, 0.5, 1};
-static double colorStroke[4] = {0, 0, 0, 1};
-static double lineWidth = 1;
-static double *path;
-static size_t pathSize;
-static size_t pathAllocated;
-
-static HAlign horAlign = HALIGN_LEFT;
-static VAlign vertAlign = VALIGN_TOP;
-static char *font;
-static double fontSize = 24;
-
-
-void background(const char *color)
-	{ heliParseColor(color, colorBack); }
-void fill(const char *color)
-	{ heliParseColor(color, colorFill); }
-void noFill()
-	{ fill("transparent"); }
-void stroke(const char *color)
-	{ heliParseColor(color, colorStroke); }
-void noStroke()
-	{ stroke("transparent"); }
-
-void strokeWeight(double weight)
-	{ lineWidth = weight; }
-
-char* rgba(double r, double g, double b, double a) {
-	static char buf[1024];
-	snprintf(buf, sizeof(buf) - 1, "%f %f %f %f", r, g, b, a);
-	return buf;
-}
-
-char* rgb(double r, double g, double b)
-	{ return rgba(r, g, b, 1); }
-
-void rect(double x, double y, double width, double height) {
-	resetPath();
-	moveTo(x, y);
-	lineTo(x + width, y);
-	lineTo(x + width, y + height);
-	lineTo(x, y + height);
-	closePath();
-}
-
-void line(double x1, double y1, double x2, double y2) {
-	resetPath();
-	moveTo(x1, y1);
-	lineTo(x2, y2);
-	strokePath();
-}
-
-void ellipse(double x, double y, double width, double height) {
-	resetPath();
-	arcPath(x, y, width, height, 0, 360);
-	closePath();
-}
-
-void point(double x, double y)
-	{ ellipse(x - lineWidth*0.25, y - lineWidth*0.25, lineWidth*0.5, lineWidth*0.5); }
-
-void arcPath(double x, double y, double w, double h, double start, double stop) {
-	double step = PI/180;
-	start *= PI/180;
-	stop *= PI/180;
-	if (start < stop) { double s = start; stop = start; start = s; }
-	for(double a = start; a < stop; a += step) {
-		double lx = x + cos(a)*w;
-		double ly = y + sin(a)*h;
-		lineTo(lx, ly);
-	}
-}
-
-void arc(double x, double y, double w, double h, double start, double stop) {
-	resetPath();
-	arcPath(x, y, w, h, start, stop);
-	strokePath();
-}
-
-void regularPolygon(double x, double y, int sides, double size) {
-	resetPath();
-	size *= 0.5;
-	moveTo(x + size, y);
-	for(int i = 1; i < sides; ++i) {
-		double a = i*PI/sides;
-		lineTo(x + size*cos(a), y + size*sin(a));
-	}
-	closePath();
-}
-
-
-void resetPath()
-	{ pathSize = 0; }
-
-static void endPath(int close, int stroke, int fill) {
-	cairo_t *cr = heliCairo;
-	if (cr && pathSize >= 8) {
-		cairo_save(cr);
-		cairo_move_to(cr, path[0], path[1]);
-		for(int i = 2; i < pathSize; i += 2)
-			cairo_line_to(cr, path[i], path[i+1]);
-		if (close)
-			cairo_close_path(cr);
-		if (fill) {
-			cairo_set_source_rgba(cr, colorFill[0], colorFill[1], colorFill[2], colorFill[3]);
-			if (stroke) cairo_fill_preserve(cr); else cairo_fill(cr);
-		}
-		if (stroke) {
-			cairo_set_line_width(cr, lineWidth);
-			cairo_set_source_rgba(cr, colorStroke[0], colorStroke[1], colorStroke[2], colorStroke[3]);
-			cairo_stroke(cr);
-		}
-		cairo_restore(cr);
-	}
-	resetPath();
-}
-
-static void pushPathPoint(double x, double y) {
-	if (pathAllocated < pathSize + 2) {
-		pathAllocated += pathAllocated/4 + 32;
-		path = realloc(path, pathAllocated);
-		memset(&path[pathSize], 0, (pathAllocated - pathSize)*sizeof(*path));
-	}
-	path[pathSize++] = x;
-	path[pathSize++] = y;
-}
-
-void closePath()
-	{ endPath(TRUE, TRUE, TRUE); }
-void strokePath()
-	{ endPath(FALSE, TRUE, FALSE); }
-void lineTo(double x, double y)
-	{ pushPathPoint(x, y); }
-void moveTo(double x, double y)
-	{ resetPath(); lineTo(x, y); }
-
-
-void textAlign(HAlign hor, VAlign vert)
-	{ horAlign = hor; vertAlign = vert; }
-void textFont(const char *f)
-	{ free(font); font = heliStringCopy(f); }
-void textSize(double size)
-	{ fontSize = size; }
-
-void text(const char *text, double x, double y) {
-	resetPath();
-
-	cairo_t *cr = heliCairo;
-	if (!cr) return;
-	cairo_save(cr);
-
-	if (font) cairo_select_font_face(cr, font, CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_NORMAL);
-	cairo_set_font_size(cr, fontSize);
-	
-	cairo_text_extents_t extents;
-	cairo_text_extents(cr, text, &extents);
-	double w = extents.x_bearing + extents.width;
-	double h = extents.y_bearing + extents.height;
-	if (horAlign  == HALIGN_CENTER) x -= w*0.5;
-	if (horAlign  == HALIGN_RIGHT ) x -= w;
-	if (vertAlign == VALIGN_CENTER) y -= h*0.5;
-	if (vertAlign == VALIGN_BOTTOM) y -= h;
-	
-	cairo_set_source_rgba(cr, colorStroke[0], colorStroke[1], colorStroke[2], colorStroke[3]);
-	cairo_move_to(cr, x, y);
-	cairo_show_text(cr, text);
-	
-	cairo_restore(cr);
-}
-
-void heliDrawingClearFrame(cairo_t *cr) {
-	cairo_save(cr);
-	cairo_set_source_rgba(cr, colorBack[0], colorBack[1], colorBack[2], 1);
-	cairo_paint(cr);
-	cairo_restore(cr);
-}
-
-void heliDrawingPrepareFrame() {
-	resetPath();
-	if (heliCairo) heliDrawingClearFrame(heliCairo);
-}
-
-void heliDrawingFinish() {
-	resetPath();
-	free(path);
-	path = NULL;
-	pathAllocated = 0;
-	free(font);
-	font = NULL;
-}
diff --git a/helianthus/drawing.h b/helianthus/drawing.h
deleted file mode 100644
index 3fa6f4a..0000000
--- a/helianthus/drawing.h
+++ /dev/null
@@ -1,48 +0,0 @@
-#ifndef HELI_DRAWING_H
-#define HELI_DRAWING_H
-
-
-#include "common.h"
-
-typedef enum _HAlign {
-	HALIGN_LEFT,
-	HALIGN_CENTER,
-	HALIGN_RIGHT
-} HAlign;
-
-typedef enum _VAlign {
-	VALIGN_TOP,
-	VALIGN_CENTER,
-	VALIGN_BOTTOM
-} VAlign;
-
-
-void background(const char *color);
-void fill(const char *color);
-void noFill();
-void stroke(const char *color);
-void noStroke();
-void strokeWeight(double weight);
-char* rgb(double r, double g, double b);
-char* rgba(double r, double g, double b, double a);
-void rect(double x, double y, double width, double height);
-void ellipse(double x, double y, double width, double height);
-void text(const char *text, double x, double y);
-void textAlign(HAlign hor, VAlign vert);
-void textFont(const char *font);
-void textSize(double size);
-void arc(double x, double y, double w, double h, double start, double stop);
-void arcPath(double x, double y, double w, double h, double start, double stop);
-void line(double x1, double y1, double x2, double y2);
-void point(double x, double y);
-void regularPolygon(double x, double y, int sides, double size);
-
-void moveTo(double x, double y);
-void lineTo(double x, double y);
-void resetPath();
-void closePath();
-void strokePath();
-
-
-#endif
-
diff --git a/helianthus/group.c b/helianthus/group.c
deleted file mode 100644
index 400bffd..0000000
--- a/helianthus/group.c
+++ /dev/null
@@ -1,209 +0,0 @@
-
-#include "private.h"
-#include "group.h"
-#include "world.h"
-
-struct _Group {
-	HeliArray sprites;
-};
-
-
-Group createGroup() {
-	Group g = calloc(1, sizeof(*g));
-	return g;
-}
-
-Group createEdgesGroupEx(double x1, double y1, double x2, double y2, double borderWidth) {
-	if (x2 < x1) { double x = x2; x2 = x1; x1 = x; }
-	if (y2 < y1) { double y = y2; y2 = y1; y1 = y; }
-	if (borderWidth < 0.1) borderWidth = 0.1;
-	
-	double b = borderWidth;
-	double w = x2 - x1 + b*2;
-	double h = y2 - y1 + b*2;
-	x1 -= b;
-	y1 -= b;
-	
-	Group g = createGroup();
-	groupAdd(g, createSpriteEx(x1, y1, w, b));
-	groupAdd(g, createSpriteEx(x1, y2, w, b));
-	groupAdd(g, createSpriteEx(x1, y1, b, h));
-	groupAdd(g, createSpriteEx(x2, y1, b, h));
-	return g;
-}
-
-Group createEdgesGroup()
-	{ return createEdgesGroupEx(0, 0, worldGetWidth(), worldGetHeight(), 10); }
-
-
-void groupDestroy(Group group) {
-	heliArrayDestroy(&group->sprites);
-	free(group);
-}
-
-void groupDestroyEx(Group group, int destroySprites) {
-	groupClearEx(group, destroySprites);
-	groupDestroy(group);
-}
-
-void groupAdd(Group group, Sprite sprite) {
-	if (groupContains(group, sprite)) return;
-	heliArrayInsert(&group->sprites, -1, sprite, NULL);
-	heliArrayInsert(heliSpriteGetGroups(sprite), -1, sprite, NULL);
-}
-
-void groupRemove(Group group, Sprite sprite) {
-	for(int i = group->sprites.count-1; i >= 0; --i)
-		if (group->sprites.items[i].value == sprite)
-			heliArrayRemove(&group->sprites, i);
-	HeliArray *groups = heliSpriteGetGroups(sprite);
-	for(int i = groups->count-1; i >= 0; --i)
-		if (groups->items[i].value == group)
-			heliArrayRemove(groups, i);
-}
-
-void groupClearEx(Group group, int destroySprites) {
-	while(groupGetCount(group) > 0) {
-		Sprite s = groupGet(group, 0);
-		groupRemove(group, s);
-		if (destroySprites) spriteDestroy(s);
-	}
-}
-
-void groupClear(Group group)
-	{ groupClearEx(group, FALSE); }
-void groupDestroyEach(Group group)
-	{ groupClearEx(group, TRUE); }
-
-int groupContains(Group group, Sprite sprite) {
-	for(int i = group->sprites.count-1; i >= 0; --i)
-		if (group->sprites.items[i].value == sprite)
-			return TRUE;
-	return FALSE;
-}
-
-int groupGetCount(Group group)
-	{ return group->sprites.count; }
-Sprite groupGet(Group group, int i)
-	{ return (Sprite)heliArrayGetValue(&group->sprites, i); }
-
-int groupOverlap(Group group, Sprite sprite)
-	{ return groupCollideEx(group, sprite, TRUE, TRUE, 0); }
-int groupCollide(Group group, Sprite sprite, double bounciness)
-	{ return groupCollideEx(group, sprite, FALSE, FALSE, bounciness); }
-int groupBounceOff(Group group, Sprite sprite, double bounciness)
-	{ return groupCollideEx(group, sprite, FALSE, TRUE, bounciness); }
-int groupPush(Group group, Sprite sprite, double bounciness)
-	{ return groupCollideEx(group, sprite, TRUE, FALSE, bounciness); }
-int groupCollideEx(Group group, Sprite sprite, int keepVelocityGroup, int keepVelocitySprite, double bounciness) {
-	int result = FALSE;
-	for(int i = 0; i < groupGetCount(group); ++i)
-		if (spriteCollideEx(groupGet(group, i), sprite, keepVelocityGroup, keepVelocitySprite, bounciness))
-			result = TRUE;
-	return result;
-}
-
-int groupOverlapGroup(Group a, Group b)
-	{ return groupCollideGroupEx(a, b, TRUE, TRUE, 0); }
-int groupCollideGroup(Group a, Group b, double bounciness)
-	{ return groupCollideGroupEx(a, b, FALSE, FALSE, bounciness); }
-int groupBounceOffGroup(Group group, Group other, double bounciness)
-	{ return groupCollideGroupEx(group, other, FALSE, TRUE, bounciness); }
-int groupPushGroup(Group group, Group other, double bounciness)
-	{ return groupCollideGroupEx(group, other, TRUE, FALSE, bounciness); }
-int groupCollideGroupEx(Group a, Group b, int keepVelocityA, int keepVelocityB, double bounciness) {
-	int result = FALSE;
-	for(int i = 0; i < groupGetCount(b); ++i)
-		if (groupCollideEx(a, groupGet(b, i), keepVelocityA, keepVelocityB, bounciness))
-			result = TRUE;
-	return result;
-}
-
-double groupGetMinDepth(Group group) {
-	if (groupGetCount(group) <= 0) return 0;
-	double md = spriteGetDepth(groupGet(group, 0));
-	for(int i = 1; i < groupGetCount(group); ++i) {
-		double d = spriteGetDepth(groupGet(group, i));
-		if (d < md) md = d;
-	}
-	return md;
-}
-
-double groupGetMaxDepth(Group group) {
-	if (groupGetCount(group) <= 0) return 0;
-	double md = spriteGetDepth(groupGet(group, 0));
-	for(int i = 1; i < groupGetCount(group); ++i) {
-		double d = spriteGetDepth(groupGet(group, i));
-		if (d > md) md = d;
-	}
-	return md;
-}
-
-
-static void foreachInt(Group group, int value, HeliSpriteEashInt func)
-	{ for(int i = 0; i < groupGetCount(group); ++i) func(groupGet(group, i), value); }
-static void foreachDouble(Group group, double value, HeliSpriteEashDouble func)
-	{ for(int i = 0; i < groupGetCount(group); ++i) func(groupGet(group, i), value); }
-static void foreachString(Group group, const char *value, HeliSpriteEashString func)
-	{ for(int i = 0; i < groupGetCount(group); ++i) func(groupGet(group, i), value); }
-
-
-void groupDestroyTimerEach(Group group, double lifetime)
-	{ foreachDouble(group, lifetime, &spriteDestroyTimer); }
-
-void groupSetVisibleEach(Group group, int visible)
-	{ foreachInt(group, visible, &spriteSetVisible); }
-void groupSetWidthEach(Group group, double width)
-	{ foreachDouble(group, width, &spriteSetWidth); }
-void groupSetHeightEach(Group group, double height)
-	{ foreachDouble(group, height, &spriteSetHeight); }
-void groupSetDepthEach(Group group, double depth)
-	{ foreachDouble(group, depth, &spriteSetDepth); }
-void groupSetVelocityXEach(Group group, double x)
-	{ foreachDouble(group, x, &spriteSetVelocityX); }
-void groupSetVelocityYEach(Group group, double y)
-	{ foreachDouble(group, y, &spriteSetVelocityY); }
-void groupSetRotateToDirectionEach(Group group, int rotateToDirection)
-	{ foreachInt(group, rotateToDirection, &spriteSetRotateToDirection); }
-void groupSetRotationEach(Group group, double rotation)
-	{ foreachDouble(group, rotation, &spriteSetRotation); }
-void groupSetRotationSpeedEach(Group group, double rotationSpeed)
-	{ foreachDouble(group, rotationSpeed, &spriteSetRotationSpeed); }
-void groupSetScaleEach(Group group, double scale)
-	{ foreachDouble(group, scale, &spriteSetScale); }
-void groupSetMirrorXEach(Group group, int mirrorX)
-	{ foreachInt(group, mirrorX, &spriteSetMirrorX); }
-void groupSetMirrorYEach(Group group, int mirrorY)
-	{ foreachInt(group, mirrorY, &spriteSetMirrorY); }
-void groupSetAnimationEach(Group group, const char *path)
-	{ foreachString(group, path, &spriteSetAnimation); }
-void groupSetShapeColorEach(Group group, const char *color)
-	{ foreachString(group, color, &spriteSetShapeColor); }
-void groupSetTintColorEach(Group group, const char *color)
-	{ foreachString(group, color, &spriteSetTintColor); }
-
-void groupPointToEach(Group group, double x, double y) {
-	for(int i = 0; i < groupGetCount(group); ++i)
-		spritePointTo(groupGet(group, i), x, y);
-}
-
-void groupSetSpeedAndDirectionEach(Group group, double speed, double angle) {
-	for(int i = 0; i < groupGetCount(group); ++i)
-		spriteSetSpeedAndDirection(groupGet(group, i), speed, angle);
-}
-
-void groupSetVelocityEach(Group group, double x, double y) {
-	for(int i = 0; i < groupGetCount(group); ++i)
-		spriteSetVelocityXY(groupGet(group, i), x, y);
-}
-
-void groupSetColliderEachEx(Group group, Collider type, double xOffset, double yOffset,
-							double widthOrRadius, double height, double rotationOffset)
-{
-	for(int i = 0; i < groupGetCount(group); ++i)
-		spriteSetColliderEx(groupGet(group, i), type, xOffset, yOffset,
-							widthOrRadius, height, rotationOffset);
-}
-
-void groupSetColliderEach(Group group, Collider type, double xOffset, double yOffset)
-	{ groupSetColliderEachEx(group, type, xOffset, yOffset, -1, -1, 0); }
diff --git a/helianthus/group.h b/helianthus/group.h
deleted file mode 100644
index 241577c..0000000
--- a/helianthus/group.h
+++ /dev/null
@@ -1,68 +0,0 @@
-#ifndef HELI_GROUP_H
-#define HELI_GROUP_H
-
-
-#include "sprite.h"
-
-
-typedef struct _Group *Group;
-
-
-Group createGroup();
-Group createEdgesGroup();
-Group createEdgesGroupEx(double x1, double y1, double x2, double y2, double borderWidth);
-
-void groupDestroy(Group group);
-void groupDestroyEx(Group group, int destroySprites);
-
-void groupAdd(Group group, Sprite sprite);
-void groupRemove(Group group, Sprite sprite);
-void groupClear(Group group);
-void groupClearEx(Group group, int destroySprites);
-int groupContains(Group group, Sprite sprite);
-int groupGetCount(Group group);
-Sprite groupGet(Group group, int i);
-
-int groupOverlap(Group group, Sprite sprite);
-int groupCollide(Group group, Sprite sprite, double bounciness);
-int groupBounceOff(Group group, Sprite sprite, double bounciness);
-int groupPush(Group group, Sprite sprite, double bounciness);
-int groupCollideEx(Group group, Sprite sprite, int keepVelocityGroup, int keepVelocitySprite, double bounciness);
-
-int groupOverlapGroup(Group a, Group b);
-int groupCollideGroup(Group a, Group b, double bounciness);
-int groupBounceOffGroup(Group group, Group other, double bounciness);
-int groupPushGroup(Group group, Group other, double bounciness);
-int groupCollideGroupEx(Group a, Group b, int keepVelocityA, int keepVelocityB, double bounciness);
-
-double groupGetMinDepth(Group group);
-double groupGetMaxDepth(Group group);
-
-void groupDestroyEach(Group group);
-void groupDestroyTimerEach(Group group, double lifetime);
-
-void groupSetVisibleEach(Group group, int visible);
-void groupSetWidthEach(Group group, double width);
-void groupSetHeightEach(Group group, double height);
-void groupSetDepthEach(Group group, double depth);
-void groupSetVelocityXEach(Group group, double x);
-void groupSetVelocityYEach(Group group, double y);
-void groupSetVelocityEach(Group group, double x, double y);
-void groupSetLifetimeEach(Group group, double lifetime);
-void groupSetRotateToDirectionEach(Group group, int rotateToDirection);
-void groupSetRotationEach(Group group, double rotation);
-void groupSetRotationSpeedEach(Group group, double rotationSpeed);
-void groupSetScaleEach(Group group, double scale);
-void groupSetMirrorXEach(Group group, int mirrorX);
-void groupSetMirrorYEach(Group group, int mirrorY);
-void groupPointToEach(Group group, double x, double y);
-void groupSetSpeedAndDirectionEach(Group group, double speed, double angle);
-void groupSetAnimationEach(Group group, const char *path);
-void groupSetShapeColorEach(Group group, const char *color);
-void groupSetTintColorEach(Group group, const char *color);
-void groupSetColliderEach(Group group, Collider type, double xOffset, double yOffset);
-void groupSetColliderEachEx(Group group, Collider type, double xOffset, double yOffset,
-							double widthOrRadius, double height, double rotationOffset);
-
-
-#endif
diff --git a/helianthus/helianthus.h b/helianthus/helianthus.h
deleted file mode 100644
index 9288436..0000000
--- a/helianthus/helianthus.h
+++ /dev/null
@@ -1,12 +0,0 @@
-#ifndef HELI_HELIANTUS_H
-#define HELI_HELIANTUS_H
-
-
-#include "common.h"
-#include "world.h"
-#include "sprite.h"
-#include "group.h"
-#include "drawing.h"
-
-
-#endif
diff --git a/helianthus/main.c b/helianthus/main.c
deleted file mode 100644
index d7c4f64..0000000
--- a/helianthus/main.c
+++ /dev/null
@@ -1,49 +0,0 @@
-
-#include <stdio.h>
-
-#include "helianthus.h"
-
-Sprite ball, brick1, brick2;
-Sound beep;
-
-void init() {
-	ball = createSpriteEx(200, 200, 64, 64);
-	spriteSetAnimation(ball, "data/sprite/breadball.png");
-	
-	brick1 = createSpriteEx(200-32, 200+64, 64, 64);
-	spriteSetAnimation(brick1, "data/sprite/bricks.png");
-	spriteSetTintColor(brick1, rgb(0, 0, 1));
-	
-	brick2 = createSpriteEx(200+32, 200+64, 64, 64);
-	spriteSetAnimation(brick2, "data/sprite/bricks.png");
-	spriteSetTintColor(brick2, rgba(1, 0, 1, 0.5));
-	
-	beep = createSound("data/sound/beep.ogg");
-}
-
-void draw() {
-	double dt = worldGetTimeStep();
-	double speed = 100;
-	
-	spritePointTo(ball, mouseX(), mouseY());
-	
-	double x = spriteGetX(ball);
-	double y = spriteGetY(ball);
-	if (keyDown("left"))  spriteSetX(ball, x - speed*dt);
-	if (keyDown("right")) spriteSetX(ball, x + speed*dt);
-	if (keyDown("up"))    spriteSetY(ball, y - speed*dt);
-	if (keyDown("down"))  spriteSetY(ball, y + speed*dt);
-	
-	spriteSetSpeedAndDirection(ball, speed/2, spriteGetRotation(ball));
-	
-	if (mouseWentDown("left")) soundPlay(beep, FALSE);
-	
-	drawSprites();
-}
-
-int main() {
-	worldSetInit(&init);
-	worldSetDraw(&draw);
-	worldRun();
-	return 0;	
-}
diff --git a/helianthus/private.h b/helianthus/private.h
deleted file mode 100644
index 34b7d47..0000000
--- a/helianthus/private.h
+++ /dev/null
@@ -1,120 +0,0 @@
-
-#include <assert.h>
-#include <string.h>
-#include <stdlib.h>
-#include <stdio.h>
-#include <ctype.h>
-#include <math.h>
-
-#include <cairo.h>
-
-#include "common.h"
-#include "sprite.h"
-
-
-// globals
-
-extern cairo_t *heliCairo;
-
-
-// string
-
-char* heliStringCopy(const char *x);
-char* heliStringConcat3(const char *a, const char *b, const char *c);
-int heliStringEndsWithLowcase(const char *s, const char *tail);
-void heliLowercase(char *x);
-void heliParseColor(const char *x, double *color);
-
-
-// pointer array
-
-typedef void (*HeliFreeCallback)(void*);
-
-typedef struct _HeliPair {
-	void *key;
-	void *value;
-	HeliFreeCallback freeKey;
-	HeliFreeCallback freeValue;
-} HeliPair;
-
-typedef struct _HeliArray {
-	HeliPair *items;
-	int count;
-	int allocated;
-} HeliArray;
-
-void heliPairInit(HeliPair *p);
-void heliPairDestroy(HeliPair *p);
-
-void heliArrayInit(HeliArray *a);
-void heliArrayClear(HeliArray *a);
-void heliArrayDestroy(HeliArray *a);
-HeliPair* heliArrayGet(HeliArray *a, int i);
-void* heliArrayGetKey(HeliArray *a, int i);
-void* heliArrayGetValue(HeliArray *a, int i);
-HeliPair* heliArrayInsert(HeliArray *a, int i, void *v, HeliFreeCallback fv);
-HeliPair* heliArrayInsertPair(HeliArray *a, int i, void *k, void *v, HeliFreeCallback fk, HeliFreeCallback fv);
-void heliArrayRemove(HeliArray *a, int i);
-
-HeliPair* heliStringmapFind(HeliArray *a, const char *k, int *gtOrEqIndex);
-HeliPair* heliStringmapGet(HeliArray *a, const char *k);
-HeliPair* heliStringmapAdd(HeliArray *a, const char *k, void *v, HeliFreeCallback fv);
-int heliStringmapRemove(HeliArray *a, const char *k);
-
-
-// animation
-
-typedef struct _HeliAnimation {
-	char *path;
-	HeliArray frames;
-	int refcount;
-} HeliAnimation;
-
-HeliAnimation *heliCreateAnimation(const char *path);
-void heliAnimationUnref(HeliAnimation *a);
-void heliAnimationFinish();
-
-
-// collider
-
-typedef struct _HeliCollider {
-	Collider type;
-	double x;
-	double y;
-	double radius;
-	double width;
-	double height;
-	double rotation;
-} HeliCollider;
-
-int heliCheckCollision(HeliCollider *a, HeliCollider *b, double *normX, double *normY);
-int heliPointCollision(HeliCollider *c, double x, double y);
-
-
-// sprite
-
-typedef void (*HeliSpriteEashInt)(Sprite, int);
-typedef void (*HeliSpriteEashDouble)(Sprite, double);
-typedef void (*HeliSpriteEashString)(Sprite, const char*);
-HeliArray* heliSpriteGetGroups(Sprite sprite);
-void heliSpriteUpdate(double dt);
-void heliSpriteFinish();
-
-
-// drawing
-
-void heliDrawingClearFrame(cairo_t *cr);
-void heliDrawingPrepareFrame();
-void heliDrawingFinish();
-
-
-// sound
-
-void heliSoundUpdate();
-void heliSoundFinish();
-
-
-// test
-
-void heliDoTests();
-
diff --git a/helianthus/sound.c b/helianthus/sound.c
deleted file mode 100644
index aa36d92..0000000
--- a/helianthus/sound.c
+++ /dev/null
@@ -1,163 +0,0 @@
-
-#include <glib.h>
-
-#include <SDL.h>
-#include <SDL_mixer.h>
-
-#include "private.h"
-#include "world.h"
-
-
-#define HELI_SOUND_CHANNELS 64
-
-
-typedef struct _HeliSoundInstance {
-	char *path;
-	Mix_Chunk *chunk;
-	int refcount;
-} HeliSoundInstance;
-
-typedef struct _HeliSoundTrashItem {
-	Mix_Chunk *chunk;
-	gint64 time;
-} HeliSoundTrashItem;
-
-struct _Sound {
-	HeliSoundInstance *instance;
-};
-
-
-static int initialized;
-static int ready;
-
-static HeliArray cache;
-static Sound channels[HELI_SOUND_CHANNELS];
-
-static HeliSoundTrashItem *trash;
-static size_t trashSize;
-
-
-static void trashAdd(Mix_Chunk *chunk) {
-	if (!chunk) return;
-	
-	gint64 time = g_get_monotonic_time() + 1000000;
-	for(int i = 0; i < trashSize; ++i)
-		if (!trash[i].chunk) 
-			{ trash[i].chunk = chunk; trash[i].time = time; return; }
-	
-	size_t prevSize = trashSize;
-	trashSize += trashSize/4 + 32;
-	trash = realloc(trash, trashSize);
-	memset(&trash[prevSize], 0, (trashSize - prevSize)*sizeof(*trash));
-	
-	trash[prevSize].chunk = chunk;
-	trash[prevSize].time = time;
-}
-
-static void trashProcess() {
-	gint64 time = g_get_monotonic_time();
-	for(int i = 0; i < trashSize; ++i)
-		if (trash[i].chunk && trash[i].time <= time)
-			{ Mix_FreeChunk(trash[i].chunk); trash[i].chunk = NULL; }
-}
-
-static void trashDestroy() {
-	for(int i = 0; i < trashSize; ++i)
-		if (trash[i].chunk) Mix_FreeChunk(trash[i].chunk);
-	trashSize = 0;
-	free(trash);
-	trash = NULL;
-}
-
-
-static void init() {
-	if (initialized) return;
-	if (SDL_Init(SDL_INIT_AUDIO) == 0) {
-		int loaded = Mix_Init(MIX_INIT_OGG | MIX_INIT_FLAC | MIX_INIT_MP3);
-		if (!(loaded & MIX_INIT_OGG )) fprintf(stderr, "helianthus: cannot initialize OGG  support\n");
-		if (!(loaded & MIX_INIT_FLAC)) fprintf(stderr, "helianthus: cannot initialize FLAC support\n");
-		if (!(loaded & MIX_INIT_MP3 )) fprintf(stderr, "helianthus: cannot initialize MP3  support\n");
-		ready = Mix_OpenAudio(44100, MIX_DEFAULT_FORMAT, 2, 1024) == 0;
-		if (!ready) fprintf(stderr, "helianthus: cannot open audio device\n");
-	}
-	initialized = TRUE;
-}
-
-static void deinit() {
-	if (!initialized) return;
-	heliArrayDestroy(&cache);
-	if (ready) Mix_CloseAudio();
-	trashDestroy();
-	Mix_Quit();
-	SDL_Quit();
-	for(int i = 0; i < HELI_SOUND_CHANNELS; ++i) channels[i] = NULL;
-	ready = FALSE;
-	initialized = FALSE;
-}
-
-
-static HeliSoundInstance* load(const char *path) {
-	HeliSoundInstance *s = calloc(1, sizeof(*s));
-	s->path = heliStringCopy(path);
-	if (ready) {
-		s->chunk = Mix_LoadWAV(path);
-		if (!s->chunk)
-			fprintf(stderr, "helianthus: cannot load sound file: %s\n", path);
-	}
-	return s;
-}
-
-static void unload(HeliSoundInstance *s) {
-	assert(!s->refcount);
-	free(s->path);
-	trashAdd(s->chunk);
-	free(s);
-}
-
-
-Sound createSound(const char *path) {
-	init();
-	HeliPair *item = heliStringmapGet(&cache, path);
-	if (!item) item = heliStringmapAdd(&cache, path, load(path), (HeliFreeCallback)&unload);
-	HeliSoundInstance *s = (HeliSoundInstance*)item->value;
-	++s->refcount;
-	
-	Sound sound = calloc(1, sizeof(*sound));
-	sound->instance = s;
-	return sound;
-}
-
-void soundDestroy(Sound sound) {
-	soundStop(sound);
-	if (--sound->instance->refcount <= 0)
-		heliStringmapRemove(&cache, sound->instance->path);
-}
-
-
-void soundPlay(Sound sound, int loop) {
-	if (!ready) return;
-	if (sound->instance->chunk) {
-		int channel = Mix_PlayChannel(-1, sound->instance->chunk, loop ? -1 : 0);
-		assert(channel < HELI_SOUND_CHANNELS);
-		if (channel >= 0 && channel < HELI_SOUND_CHANNELS)
-			channels[channel] = sound;
-	}
-}
-
-void soundStop(Sound sound) {
-	for(int i = 0; i < HELI_SOUND_CHANNELS; ++i) {
-		if (channels[i] == sound) {
-			Mix_Pause(i);
-			Mix_HaltChannel(i);
-			channels[i] = NULL;
-		}
-	}
-}
-
-
-void heliSoundUpdate()
-	{ trashProcess(); }
-
-void heliSoundFinish()
-	{ deinit(); }
-
diff --git a/helianthus/sprite.c b/helianthus/sprite.c
deleted file mode 100644
index eb14663..0000000
--- a/helianthus/sprite.c
+++ /dev/null
@@ -1,441 +0,0 @@
-
-#include <cairo.h>
-
-#include "private.h"
-
-#include "sprite.h"
-#include "world.h"
-#include "group.h"
-
-struct _Sprite {
-	double x;
-	double y;
-	double rotation;
-	double width;
-	double height;
-	double scale;
-	
-	double vx;
-	double vy;
-	double rotationSpeed;
-	
-	HeliCollider collider;
-	double bounciness;
-	
-	int rotateToDirection;
-	int mirrorX;
-	int mirrorY;
-	double depth;
-	double lifeTime;
-	int visible;
-	int debug;
-	
-	double shapeColor[4];
-	double tintColor[4];
-	
-	int playing;
-	int frame;
-	
-	HeliArray groups;
-	
-	HeliAnimation *animation;
-};
-
-static HeliArray sprites;
-static HeliArray spritesSorted;
-
-
-static void prepareCollider(Sprite sprite, HeliCollider *collider) {
-	collider->type = sprite->collider.type;
-	collider->x = sprite->collider.x + sprite->x;
-	collider->y = sprite->collider.y + sprite->y;
-	collider->width = sprite->collider.width >= 0 ? sprite->collider.width : sprite->width;
-	collider->height = sprite->collider.height >= 0 ? sprite->collider.height : sprite->height;
-	collider->radius = sprite->collider.radius >= 0 ? sprite->collider.radius : collider->width;
-	collider->rotation = sprite->collider.rotation + sprite->rotation;
-}
-
-
-
-Sprite createSpriteEx(double x, double y, double width, double height) {
-	Sprite s = calloc(1, sizeof(*s));
-	s->x = x;
-	s->y = y;
-	s->width = width;
-	s->height = height;
-	
-	s->scale = 1;
-	s->collider.type = COLLIDER_RECTANGLE;
-	s->collider.width = s->collider.height = s->collider.radius = -1;
-	
-	s->mirrorX = 1;
-	s->mirrorY = 1;
-	s->lifeTime = -1;
-	s->visible = TRUE;
-	
-	s->shapeColor[0] = s->shapeColor[1] = s->shapeColor[2] = 0.5;
-	s->shapeColor[3] = 1;
-	s->tintColor[0] = s->tintColor[1] = s->tintColor[2] = s->tintColor[3] = 1;
-	
-	heliArrayInsert(&sprites, -1, s, NULL);
-	heliArrayInsert(&spritesSorted, -1, s, NULL);
-	
-	return s;
-}
-
-Sprite createSprite(double x, double y)
-	{ return createSpriteEx(x, y, 100, 100); }
-
-void spriteDestroy(Sprite sprite) {
-	while(sprite->groups.count > 0)
-		groupRemove((Group)sprite->groups.items[0].value, sprite);
-	for(int i = 0; i < sprites.count; ++i)
-		if (sprites.items[i].value == sprite)
-			{ heliArrayRemove(&sprites, i); break; }
-	for(int i = 0; i < spritesSorted.count; ++i)
-		if (spritesSorted.items[i].value == sprite)
-			{ heliArrayRemove(&spritesSorted, i); break; }
-	if (sprite->animation)
-		heliAnimationUnref(sprite->animation);
-	free(sprite);
-}
-
-void spriteDestroyTimer(Sprite sprite, double lifeTime) {
-	if (lifeTime <= 0) { spriteDestroy(sprite); return; }
-	sprite->lifeTime = lifeTime;
-}
-
-double spriteGetX(Sprite sprite) { return sprite->x; }
-void spriteSetX(Sprite sprite, double x) { sprite->x = x; }
-
-double spriteGetY(Sprite sprite) { return sprite->y; }
-void spriteSetY(Sprite sprite, double y) { sprite->y = y; }
-
-double spriteGetVelocityX(Sprite sprite) { return sprite->vx; }
-void spriteSetVelocityX(Sprite sprite, double x)
-	{ spriteSetVelocityXY(sprite, x, sprite->vy); }
-
-double spriteGetVelocityY(Sprite sprite) { return sprite->vy; }
-void spriteSetVelocityY(Sprite sprite, double y)
-	{ spriteSetVelocityXY(sprite, sprite->vx, y); }
-
-double spriteGetScale(Sprite sprite) { return sprite->scale; }
-void spriteSetScale(Sprite sprite, double scale) { sprite->scale = scale; }
-
-double spriteGetWidth(Sprite sprite) { return sprite->width; }
-void spriteSetWidth(Sprite sprite, double width)
-	{ sprite->width = width > 0 ? width : 0; }
-
-double spriteGetHeight(Sprite sprite) { return sprite->height; }
-void spriteSetHeight(Sprite sprite, double height)
-	{ sprite->height = height > 0 ? height : 0; }
-
-int spriteGetRotateToDirection(Sprite sprite) { return sprite->rotateToDirection; }
-void spriteSetRotateToDirection(Sprite sprite, int rotateToDirection) {
-	if (rotateToDirection) {
-		sprite->rotateToDirection = TRUE;
-		sprite->rotation = spriteGetDirection(sprite);
-	} else {
-		sprite->rotateToDirection = FALSE;
-	}
-}
-
-double spriteGetRotation(Sprite sprite) { return sprite->rotation; }
-void spriteSetRotation(Sprite sprite, double rotation)
-	{ if (!sprite->rotateToDirection) sprite->rotation = rotation; }
-
-double spriteGetRotationSpeed(Sprite sprite) { return sprite->rotationSpeed; }
-void spriteSetRotationSpeed(Sprite sprite, double rotationSpeed)
-	{ sprite->rotationSpeed = rotationSpeed; }
-
-int spriteGetMirrorX(Sprite sprite) { return sprite->mirrorX; }
-void spriteSetMirrorX(Sprite sprite, int mirrorX)
-	{ sprite->mirrorX = mirrorX < 0 ? -1 : 1; }
-
-int spriteGetMirrorY(Sprite sprite) { return sprite->mirrorY; }
-void spriteSetMirrorY(Sprite sprite, int mirrorY)
-	{ sprite->mirrorY = mirrorY < 0 ? -1 : 1; }
-
-double spriteGetDepth(Sprite sprite) { return sprite->depth; }
-void spriteSetDepth(Sprite sprite, double depth)
-	{ sprite->depth = depth; }
-
-int spriteGetVisible(Sprite sprite) { return sprite->visible; }
-void spriteSetVisible(Sprite sprite, int visible)
-	{ sprite->visible = visible != FALSE; }
-
-int spriteGetDebug(Sprite sprite) { return sprite->debug; }
-void spriteSetDebug(Sprite sprite, int debug)
-	{ sprite->debug = debug != FALSE; }
-
-int spriteOverlap(Sprite a, Sprite b)
-	{ return spriteCollideEx(a, b, TRUE, TRUE, 0); }
-int spriteCollide(Sprite a, Sprite b, double bounciness)
-	{ return spriteCollideEx(a, b, FALSE, FALSE, bounciness); }
-int spriteBounceOff(Sprite sprite, Sprite other, double bounciness)
-	{ return spriteCollideEx(sprite, other, FALSE, TRUE, bounciness); }
-int spritePush(Sprite sprite, Sprite other, double bounciness)
-	{ return spriteCollideEx(sprite, other, TRUE, FALSE, bounciness); }
-
-int spriteCollideEx(Sprite a, Sprite b, int keepVelocityA, int keepVelocityB, double bounciness) {
-	#warning "TODO: spriteCollision: not implemented yet"
-	return FALSE;
-}
-
-
-double spriteGetBounciness(Sprite sprite) { return sprite->bounciness; }
-void spriteSetBounciness(Sprite sprite, double bounciness)
-	{ sprite->bounciness = bounciness > 0 ? bounciness : 0; }
-
-void spriteSetColliderEx(Sprite sprite, Collider type, double xOffset, double yOffset,
-						 double widthOrRadius, double height, double rotationOffset)
-{
-	sprite->collider.type = type;
-	sprite->collider.x = xOffset;
-	sprite->collider.y = yOffset;
-	sprite->collider.width = sprite->collider.radius = widthOrRadius;
-	sprite->collider.height = height;
-	sprite->collider.rotation = rotationOffset;
-}
-
-void spriteSetCollider(Sprite sprite, Collider type, double xOffset, double yOffset)
-	{ spriteSetColliderEx(sprite, type, xOffset, yOffset, -1, -1, 0); }
-
-void spriteSetAnimation(Sprite sprite, const char *path) {
-	HeliAnimation *prev = sprite->animation;
-	sprite->animation = heliCreateAnimation(path);
-	if (prev) heliAnimationUnref(prev);
-	spriteSetFrame(sprite, sprite->frame);
-}
-
-void spritePlay(Sprite sprite) { sprite->playing = TRUE; }
-void spritePause(Sprite sprite) { sprite->playing = FALSE; }
-void spriteNextFrame(Sprite sprite) { spriteSetFrame(sprite, sprite->frame + 1); }
-
-void spriteSetFrame(Sprite sprite, int frame) {
-	sprite->frame = frame >= 0 && sprite->animation && sprite->animation->frames.count > 0
-				  ? frame % sprite->animation->frames.count : 0;
-}
-
-void spriteSetShapeColor(Sprite sprite, const char *color)
-	{ heliParseColor(color, sprite->shapeColor); }
-void spriteSetTintColor(Sprite sprite, const char *color)
-	{ heliParseColor(color, sprite->tintColor); }
-
-void spriteSetVelocityXY(Sprite sprite, double x, double y) {
-	sprite->vx = x;
-	sprite->vy = y;
-	if (sprite->rotateToDirection)
-		sprite->rotation = spriteGetDirection(sprite);
-}
-
-void spriteSetSpeedAndDirection(Sprite sprite, double speed, double angle) {
-	double a = angle*(PI/180);
-	spriteSetVelocityXY(sprite, cos(a)*speed, sin(a)*speed);
-}
-
-double spriteGetSpeed(Sprite sprite)
-	{ return sqrt(sprite->vx*sprite->vx + sprite->vy*sprite->vy); }
-double spriteGetDirection(Sprite sprite) {
-	return fabs(sprite->vx) > 1e-6 || fabs(sprite->vy) > 1e-6
-	     ? atan2(sprite->vy, sprite->vx)*(180/PI) : 0;
-}
-void spritePointTo(Sprite sprite, double x, double y)
-	{ spriteSetRotation( sprite, atan2(y - sprite->y, x - sprite->x)*(180/PI) ); }
-
-double spriteGetScaledWidth(Sprite sprite)
-	{ return sprite->width * sprite->scale; }
-double spriteGetScaledHeight(Sprite sprite)
-	{ return sprite->height * sprite->scale; }
-
-
-
-int worldGetSpriteCount()
-	{ return sprites.count; }
-
-Sprite worldGetSprite(int i)
-	{ return (Sprite)heliArrayGetValue(&sprites, i); }
-
-
-static void drawSpriteDebug(cairo_t *cr, Sprite s) {
-	cairo_save(cr);
-	cairo_set_line_width(cr, 0.5);
-	cairo_translate(cr, s->x, s->y);
-	cairo_rotate(cr, s->rotation*(PI/180));
-	cairo_scale(cr, s->scale*s->mirrorX, s->scale*s->mirrorY);
-	
-	double hw = s->width*0.5;
-	double hh = s->height*0.5;
-
-	cairo_set_source_rgba(cr, 0, 0, 0, 0.75);
-	cairo_move_to(cr, -hw, -hh);
-	cairo_line_to(cr,  hw, -hh);
-	cairo_line_to(cr,  hw,  hh);
-	cairo_line_to(cr, -hw,  hh);
-	cairo_close_path(cr);
-	cairo_stroke(cr);
-
-	cairo_move_to(cr, -hw*0.25, 0);
-	cairo_line_to(cr,  hw*0.25, 0);
-	cairo_move_to(cr, 0, -hh*0.25);
-	cairo_line_to(cr, 0,  hh*0.25);
-	cairo_stroke(cr);
-	
-	char buf[1024];
-	snprintf(buf, sizeof(buf)-1, "%lf", s->depth);
-	
-	double s1 = hw*0.25;
-	double s2 = hh*0.5;
-	cairo_set_font_size(cr, s1 < s2 ? s1 : s2);
-
-	cairo_move_to(cr, -hw*0.9, -hh*0.5);
-	cairo_show_text(cr, buf);
-
-	cairo_restore(cr);
-}
-
-static void drawSprite(cairo_t *cr, Sprite s) {
-	cairo_save(cr);
-	cairo_translate(cr, s->x, s->y);
-	cairo_rotate(cr, s->rotation*(PI/180));
-	cairo_scale(cr, s->scale*s->mirrorX, s->scale*s->mirrorY);
-	
-	double hw = s->width*0.5;
-	double hh = s->height*0.5;
-	
-	cairo_surface_t *frame = s->animation
-						   ? (cairo_surface_t*)heliArrayGetValue(&s->animation->frames, s->frame) : NULL;
-
-	double a = s->tintColor[3];
-	int tint = fabs(s->tintColor[0] - 1) > 1e-5
-			|| fabs(s->tintColor[1] - 1) > 1e-5
-			|| fabs(s->tintColor[2] - 1) > 1e-5;
-	int alpha = fabs(a) > 1e-5;
-	int visible = fabs(a) > 1e-5;
-	
-	if (visible) {
-		if (tint) cairo_push_group(cr);
-		
-		if (frame) {
-			// image
-			double ihw = cairo_image_surface_get_width(frame)*0.5;
-			double ihh = cairo_image_surface_get_height(frame)*0.5;
-			if (ihw > 1e-6 && ihh > 1e-6) {
-				cairo_save(cr);
-				cairo_scale(cr, hw/ihw, hh/ihh);
-				cairo_set_source_surface(cr, frame, -ihw, -ihh);
-				if (alpha) cairo_paint_with_alpha(cr, a); else cairo_paint(cr);
-				cairo_restore(cr);
-			}
-		} else {
-			// rectangle
-			cairo_set_source_rgba(cr, s->shapeColor[0], s->shapeColor[1], s->shapeColor[2], s->shapeColor[3]*a);
-			cairo_move_to(cr, -hw, -hh);
-			cairo_line_to(cr,  hw, -hh);
-			cairo_line_to(cr,  hw,  hh);
-			cairo_line_to(cr, -hw,  hh);
-			cairo_close_path(cr);
-			cairo_fill(cr);
-		}
-		
-		if (tint) {
-			cairo_pattern_t *spriteGroup = cairo_pop_group(cr);
-			cairo_push_group(cr);
-			cairo_set_source(cr, spriteGroup);
-			cairo_paint(cr);
-			cairo_set_source_rgba(cr, s->tintColor[0], s->tintColor[1], s->tintColor[2], 1);
-			cairo_set_operator(cr, CAIRO_OPERATOR_MULTIPLY);
-			cairo_mask(cr, spriteGroup);
-			cairo_pop_group_to_source(cr);
-			cairo_paint(cr);
-			cairo_pattern_destroy(spriteGroup);
-		}
-	}
-	
-	cairo_restore(cr);
-}
-
-void drawSprites() {
-	// sort
-	int found = TRUE;
-	while(found) {
-		found = FALSE;
-		// forward
-		for(int i = 1; i < spritesSorted.count; ++i) {
-			if ( ((Sprite)spritesSorted.items[i-1].value)->depth
-			   < ((Sprite)spritesSorted.items[i  ].value)->depth )
-			{
-				void *x = spritesSorted.items[i].value;
-				spritesSorted.items[i].value = spritesSorted.items[i-1].value;
-				spritesSorted.items[i-1].value = x;
-				found = TRUE;
-			}
-		}
-		if (!found) break;
-		// backward
-		found = FALSE;
-		for(int i = spritesSorted.count - 1; i > 0; --i) {
-			if ( ((Sprite)spritesSorted.items[i-1].value)->depth
-			   < ((Sprite)spritesSorted.items[i  ].value)->depth )
-			{
-				void *x = spritesSorted.items[i].value;
-				spritesSorted.items[i].value = spritesSorted.items[i-1].value;
-				spritesSorted.items[i-1].value = x;
-				found = TRUE;
-			}
-		}
-	}
-	
-	if (heliCairo) {
-		// draw
-		for(int i = 0; i < spritesSorted.count; ++i) {
-			Sprite s = (Sprite)(spritesSorted.items[i].value);
-			if (s->visible) drawSprite(heliCairo, s);
-		}
-		// draw debug marks
-		for(int i = 0; i < spritesSorted.count; ++i) {
-			Sprite s = (Sprite)(spritesSorted.items[i].value);
-			if (s->debug) drawSpriteDebug(heliCairo, s);
-		}
-	}
-}
-
-int mouseIsOver(Sprite sprite) {
-	HeliCollider collider;
-	prepareCollider(sprite, &collider);
-	return heliPointCollision(&collider, mouseX(), mouseY());
-}
-
-void heliSpriteUpdate(double dt) {
-	// auto-remove
-	for(int i = sprites.count - 1; i > 0; --i) {
-		Sprite s = (Sprite)sprites.items[i].value;
-		if (s->lifeTime >= 0) {
-			s->lifeTime -= dt;
-			if (s->lifeTime <= 1e-5)
-				spriteDestroy(s);
-		}
-	}
-	
-	// update
-	for(int i = 0; i < sprites.count; ++i) {
-		Sprite s = (Sprite)sprites.items[i].value;
-		s->x += s->vx*dt;
-		s->y += s->vy*dt;
-		if (!s->rotateToDirection)
-			s->rotation += s->rotationSpeed*dt;
-		if (s->playing) spriteNextFrame(s);
-	}
-}
-
-HeliArray* heliSpriteGetGroups(Sprite sprite)
-	{ return &sprite->groups; }
-
-void heliSpriteFinish() {
-	while(worldGetSpriteCount())
-		{ spriteDestroy(worldGetSprite(0)); }
-	heliArrayDestroy(&sprites);
-	heliArrayDestroy(&spritesSorted);
-}
-
-
diff --git a/helianthus/sprite.h b/helianthus/sprite.h
deleted file mode 100644
index aa5f28c..0000000
--- a/helianthus/sprite.h
+++ /dev/null
@@ -1,97 +0,0 @@
-#ifndef HELI_SPRITE_H
-#define HELI_SPRITE_H
-
-
-#include "common.h"
-
-typedef struct _Sprite *Sprite;
-
-
-typedef enum _Collider {
-	COLLIDER_RECTANGLE,
-	COLLIDER_CIRCLE
-} Collider;
-
-Sprite createSprite(double x, double y);
-Sprite createSpriteEx(double x, double y, double width, double height);
-
-void spriteDestroy(Sprite sprite);
-void spriteDestroyTimer(Sprite sprite, double lifetime);
-
-double spriteGetX(Sprite sprite);
-void spriteSetX(Sprite sprite, double x);
-
-double spriteGetY(Sprite sprite);
-void spriteSetY(Sprite sprite, double y);
-
-double spriteGetVelocityX(Sprite sprite);
-void spriteSetVelocityX(Sprite sprite, double x);
-
-double spriteGetVelocityY(Sprite sprite);
-void spriteSetVelocityY(Sprite sprite, double y);
-
-double spriteGetScale(Sprite sprite);
-void spriteSetScale(Sprite sprite, double scale);
-
-double spriteGetWidth(Sprite sprite);
-void spriteSetWidth(Sprite sprite, double width);
-
-double spriteGetHeight(Sprite sprite);
-void spriteSetHeight(Sprite sprite, double height);
-
-int spriteGetRotateToDirection(Sprite sprite);
-void spriteSetRotateToDirection(Sprite sprite, int rotateToDirection);
-
-double spriteGetRotation(Sprite sprite);
-void spriteSetRotation(Sprite sprite, double rotation);
-
-double spriteGetRotationSpeed(Sprite sprite);
-void spriteSetRotationSpeed(Sprite sprite, double rotationSpeed);
-
-int spriteGetMirrorX(Sprite sprite);
-void spriteSetMirrorX(Sprite sprite, int mirrorX);
-
-int spriteGetMirrorY(Sprite sprite);
-void spriteSetMirrorY(Sprite sprite, int mirrorY);
-
-double spriteGetDepth(Sprite sprite);
-void spriteSetDepth(Sprite sprite, double depth);
-
-int spriteGetVisible(Sprite sprite);
-void spriteSetVisible(Sprite sprite, int visible);
-
-int spriteGetDebug(Sprite sprite);
-void spriteSetDebug(Sprite sprite, int debug);
-
-int spriteOverlap(Sprite a, Sprite b);
-int spriteCollide(Sprite a, Sprite b, double bounciness);
-int spriteBounceOff(Sprite sprite, Sprite other, double bounciness);
-int spritePush(Sprite sprite, Sprite other, double bounciness);
-int spriteCollideEx(Sprite a, Sprite b, int keepVelocityA, int keepVelocityB, double bounciness);
-
-double spriteGetBounciness(Sprite sprite);
-void spriteSetBounciness(Sprite sprite, double bounciness);
-
-void spriteSetCollider(Sprite sprite, Collider type, double xOffset, double yOffset);
-void spriteSetColliderEx(Sprite sprite, Collider type, double xOffset, double yOffset,
-						 double widthOrRadius, double height, double rotationOffset);
-
-void spriteSetAnimation(Sprite sprite, const char *path);
-void spritePlay(Sprite sprite);
-void spritePause(Sprite sprite);
-void spriteNextFrame(Sprite sprite);
-void spriteSetFrame(Sprite sprite, int frame);
-void spriteSetShapeColor(Sprite sprite, const char *color);
-void spriteSetTintColor(Sprite sprite, const char *color);
-
-void spriteSetVelocityXY(Sprite sprite, double x, double y);
-void spriteSetSpeedAndDirection(Sprite sprite, double speed, double angle);
-double spriteGetSpeed(Sprite sprite);
-double spriteGetDirection(Sprite sprite);
-void spritePointTo(Sprite sprite, double x, double y);
-
-double spriteGetScaledWidth(Sprite sprite);
-double spriteGetScaledHeight(Sprite sprite);
-
-
-#endif
diff --git a/helianthus/test.c b/helianthus/test.c
deleted file mode 100644
index 713f2cd..0000000
--- a/helianthus/test.c
+++ /dev/null
@@ -1,60 +0,0 @@
-
-#include "private.h"
-
-//#define HELI_DO_TESTS
-
-#ifndef HELI_DO_TESTS
-void heliDoTests() { }
-#else
-
-
-static printStringset(HeliArray *a) {
-	for(int i = 0; i < a->count; ++i)
-		printf("  %s\n", (const char*)a->items[i].key);
-}
-
-static void testStringSet() {
-	printf("-- testStringSet\n");
-	
-	static char *strings[] = {
-		"hello",
-		"apple",
-		"orange",
-		"pineapple",
-		"potato",
-		"carrot",
-		"grape",
-		"cucumber"
-	};
-	
-	HeliArray a = {};
-	for(int i = 0; i < (int)(sizeof(strings)/sizeof(*strings)); ++i)
-		heliStringmapAdd(&a, strings[i], NULL, NULL);
-	
-	printf("  fill:\n");
-	printStringset(&a);
-	
-	printf("\n -remove %s:\n", "hello");
-	heliStringmapRemove(&a, "hello");
-	printStringset(&a);
-
-	printf("\n -remove %s:\n", "apple");
-	heliStringmapRemove(&a, "apple");
-	printStringset(&a);
-	
-	printf("\n -remove %s:\n", "potato");
-	heliStringmapRemove(&a, "potato");
-	printStringset(&a);
-	
-	heliArrayDestroy(&a);
-
-	printf("-- end\n");
-}
-
-void heliDoTests() {
-	printf("---- doTests\n");
-	testStringSet();
-	printf("---- end\n");
-}
-
-#endif
diff --git a/helianthus/world.c b/helianthus/world.c
deleted file mode 100644
index a7b9896..0000000
--- a/helianthus/world.c
+++ /dev/null
@@ -1,322 +0,0 @@
-
-#include <glib.h>
-#include <gtk/gtk.h>
-#include <gdk/gdk.h>
-
-#include "private.h"
-
-#include "world.h"
-
-
-static GtkWidget *window;
-
-static int started;
-static int stopped;
-static unsigned long long frameCount;
-static gint64 startTime;
-static gint64 currentTime;
-
-static Callback initCallback;
-static Callback drawCallback;
-
-static cairo_surface_t *cairoSurface;
-static int width = 400;
-static int height = 400;
-static double frameRate = 30;
-
-static int cameraEnabled;
-static double cameraX;
-static double cameraY;
-static double cameraZoom = 1;
-
-static HeliArray keysPressed;
-static HeliArray keysPressedInFrame;
-static HeliArray keysReleasedInFrame;
-static HeliArray buttonsPressed;
-static HeliArray buttonsPressedInFrame;
-static HeliArray buttonsReleasedInFrame;
-
-static int mouseMovedInFrame;
-static double _mouseX;
-static double _mouseY;
-
-static char* buttonNames[] = {
-	"left",
-	"middle",
-	"right" };
-static int buttonsCount = (int)(sizeof(buttonNames)/sizeof(*buttonNames));
-
-
-
-int keyDown(const char *code)
-	{ return heliStringmapGet(&keysPressed, code) != NULL; }
-int keyWentDown(const char *code)
-	{ return heliStringmapGet(&keysPressedInFrame, code) != NULL; }
-int keyWentUp(const char *code)
-	{ return heliStringmapGet(&keysReleasedInFrame, code) != NULL; }
-
-int mouseDidMove()
-	{ return mouseMovedInFrame; }
-int mouseDown(const char *code)
-	{ return heliStringmapGet(&buttonsPressed, code) != NULL; }
-int mouseWentDown(const char *code)
-	{ return heliStringmapGet(&buttonsPressedInFrame, code) != NULL; }
-int mouseWentUp(const char *code)
-	{ return heliStringmapGet(&buttonsReleasedInFrame, code) != NULL; }
-double mouseX()
-	{ return _mouseX; }
-double mouseY()
-	{ return _mouseY; }
-
-int mousePressedOver(Sprite sprite)
-	{ return buttonsPressed.count && mouseIsOver(sprite); }
-
-static void resize(int w, int h) {
-	width  = w > 200 ? w : 100;
-	height = h > 200 ? h : 200;
-	if (started) {
-		gtk_window_set_default_size(GTK_WINDOW(window), width, height);
-		gtk_widget_set_size_request(window, width, height);
-	}
-}
-	
-int worldGetWidth()
-	{ return width; }
-void worldSetWidth(int w)
-	{ resize(w, height); }
-
-int worldGetHeight()
-	{ return height; }
-void worldSetHeight(int h)
-	{ resize(width, h); }
-
-double worldGetFrameRate()
-	{ return frameRate; }
-void worldSetFrameRate(double frameRate) {
-	if (!(frameRate > 1)) frameRate = 1;
-	if (!(frameRate < 100)) frameRate = 100;
-}
-
-double worldGetTimeStep()
-	{ return 1/frameRate; }
-
-int worldGetFrameCount()
-	{ return (int)frameCount; }
-double worldGetSeconds()
-	{ return started ? (currentTime - startTime)*1e-6 : 0.0; }
-
-void worldSetInit(Callback init)
-	{ initCallback = init; }
-void worldSetDraw(Callback draw)
-	{ drawCallback = draw; }
-void worldStop()
-	{ if (started) stopped = TRUE; }
-
-
-void cameraOn()
-	{ cameraEnabled = TRUE; }
-void cameraOff()
-	{ cameraEnabled = FALSE; }
-int cameraIsActive()
-	{ return cameraEnabled; }
-
-double cameraMouseX()
-	{ return _mouseX/cameraZoom + cameraX; }
-double cameraMouseY()
-	{ return _mouseY/cameraZoom + cameraY; }
-
-double cameraGetX()
-	{ return cameraX; }
-void cameraSetX(double x)
-	{ cameraX = x; }
-
-double cameraGetY()
-	{ return cameraY; }
-void cameraSetY(double y)
-	{ cameraY = y; }
-
-double cameraGetZoom()
-	{ return cameraZoom; }
-void cameraSetZoom(double x)
-	{ cameraZoom = x > 1e-6 ? x : 1e-6; }
-
-static gboolean idle(gpointer data G_GNUC_UNUSED) {
-	if (stopped) {
-		if (window) {
-			gtk_window_close(GTK_WINDOW(window));
-			window = NULL;
-		}
-		return FALSE;
-	}
-	gtk_widget_queue_draw(window);
-	return TRUE;
-}
-
-static gboolean draw(GtkWidget *widget G_GNUC_UNUSED, cairo_t *cr, gpointer data G_GNUC_UNUSED) {
-	int doFrame = FALSE;
-	
-	if ( cairoSurface
-	  && cairo_image_surface_get_width(cairoSurface) != width
-	  && cairo_image_surface_get_height(cairoSurface) != height )
-		{ cairo_surface_destroy(cairoSurface); cairoSurface = NULL; }
-	if (!cairoSurface) {
-		cairoSurface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
-		doFrame = TRUE;
-	}
-
-	if (frameCount == 0) {
-		currentTime = startTime = g_get_monotonic_time();
-		doFrame = TRUE;
-	}
-
-	double dt = 1/frameRate;
-	gint64 timeStep = (gint64)round(dt*1e6);
-	gint64 newTime = g_get_monotonic_time();
-	if (currentTime < newTime)
-		doFrame = TRUE;
-	
-	if (doFrame) {
-		if (frameCount == 0) heliDoTests();
-
-		heliCairo = cairo_create(cairoSurface);
-		heliDrawingPrepareFrame();
-		if (drawCallback) drawCallback();
-		cairo_surface_flush(cairoSurface);
-		cairo_destroy(heliCairo);
-		heliCairo = NULL;
-		
-		currentTime += timeStep;
-		++frameCount;
-		heliSpriteUpdate(dt);
-		heliSoundUpdate();
-		
-		heliArrayClear(&keysPressedInFrame);
-		heliArrayClear(&keysReleasedInFrame);
-		heliArrayClear(&buttonsPressedInFrame);
-		heliArrayClear(&buttonsReleasedInFrame);
-		
-		if (stopped) g_idle_add_full(G_PRIORITY_DEFAULT, idle, NULL, NULL);
-	}
-	
-	gint64 delta = newTime - currentTime - 2000000;
-	if (delta > 0) {
-		startTime += delta;
-		currentTime += delta;
-	}
-	
-	heliDrawingClearFrame(cr);
-	cairo_save(cr);
-	cairo_set_source_surface(cr, cairoSurface, 0, 0);
-	cairo_paint(cr);
-	cairo_restore(cr);
-	
-	if (!stopped) gtk_widget_queue_draw(window);
-	
-	delta = currentTime - g_get_monotonic_time();
-	if (delta > 100) g_usleep(delta - 100);
-	
-	return TRUE;
-}
-
-static gboolean handleEvent(GtkWidget *widget G_GNUC_UNUSED, GdkEvent *event, gpointer data G_GNUC_UNUSED) {
-	gchar *keyname;
-	int button;
-	
-	switch(event->type) {
-	case GDK_KEY_PRESS:
-		keyname = heliStringCopy( gdk_keyval_name(event->key.keyval) );
-		heliLowercase(keyname);
-		heliStringmapAdd(&keysPressed, keyname, NULL, NULL);
-		heliStringmapAdd(&keysPressedInFrame, keyname, NULL, NULL);
-		free(keyname);
-		return TRUE;
-	case GDK_KEY_RELEASE:
-		keyname = heliStringCopy( gdk_keyval_name(event->key.keyval) );
-		heliLowercase(keyname);
-		heliStringmapRemove(&keysPressed, keyname);
-		heliStringmapAdd(&keysReleasedInFrame, keyname, NULL, NULL);
-		free(keyname);
-		return TRUE;
-	case GDK_BUTTON_PRESS:
-		button = event->button.button;
-		if (button >= 1 && button <= buttonsCount) {
-			heliStringmapAdd(&buttonsPressed, buttonNames[button - 1], NULL, NULL);
-			heliStringmapAdd(&buttonsPressedInFrame, buttonNames[button - 1], NULL, NULL);
-		}
-		_mouseX = event->button.x;
-		_mouseY = event->button.y;
-		return TRUE;
-	case GDK_BUTTON_RELEASE:
-		button = event->button.button;
-		if (button >= 1 && button <= buttonsCount) {
-			heliStringmapRemove(&buttonsPressed, buttonNames[button - 1]);
-			heliStringmapAdd(&buttonsReleasedInFrame, buttonNames[button - 1], NULL, NULL);
-		}
-		_mouseX = event->button.x;
-		_mouseY = event->button.y;
-		return TRUE;
-	case GDK_MOTION_NOTIFY:
-		_mouseX = event->motion.x;
-		_mouseY = event->motion.y;
-		return TRUE;
-	case GDK_DELETE:
-		stopped = TRUE;
-		window = NULL;
-		break;
-	default:
-		break;
-	}
-	return FALSE;
-}
-
-static void activate(GtkApplication* app, gpointer data G_GNUC_UNUSED) {
-	window = gtk_application_window_new(app);
-	g_signal_connect(window, "draw", G_CALLBACK(draw), NULL);
-	g_signal_connect(window, "event", G_CALLBACK(handleEvent), NULL);
-	gtk_window_set_resizable(GTK_WINDOW(window), FALSE);
-	gtk_window_set_default_size(GTK_WINDOW(window), width, height);
-	gtk_widget_add_events( window,
-						   GDK_POINTER_MOTION_MASK
-						 | GDK_BUTTON_PRESS_MASK
-						 | GDK_BUTTON_RELEASE_MASK
-						 | GDK_KEY_PRESS_MASK
-						 | GDK_KEY_RELEASE_MASK );
-	gtk_widget_set_size_request(window, width, height);
-	gtk_widget_show(window);
-
-	currentTime = startTime = 0;
-	if (initCallback) initCallback();
-	g_idle_add(idle, NULL);
-}
-
-void worldRun() {
-	if (started) return;
-	started = TRUE;
-	stopped = FALSE;
-
-	frameCount = 0;
-	srand(time(NULL));
-
-	GtkApplication *application = gtk_application_new(NULL, 0);
-	g_signal_connect(application, "activate", G_CALLBACK(activate), NULL);
-	g_application_run(G_APPLICATION(application), 0, NULL);
-	g_object_unref(application);
-	
-	heliSpriteFinish();
-	heliDrawingFinish();
-	heliAnimationFinish();
-	heliSoundFinish();
-	
-	if (cairoSurface) cairo_surface_destroy(cairoSurface);
-	cairoSurface = NULL;
-	
-	heliArrayDestroy(&keysPressed);
-	heliArrayDestroy(&keysPressed);
-	heliArrayDestroy(&keysPressedInFrame);
-	heliArrayDestroy(&keysReleasedInFrame);
-	heliArrayDestroy(&buttonsPressed);
-	heliArrayDestroy(&buttonsPressedInFrame);
-	heliArrayDestroy(&buttonsReleasedInFrame);
-	
-	started = FALSE;
-}
diff --git a/helianthus/world.h b/helianthus/world.h
deleted file mode 100644
index c01e67f..0000000
--- a/helianthus/world.h
+++ /dev/null
@@ -1,74 +0,0 @@
-#ifndef HELI_WORLD_H
-#define HELI_WORLD_H
-
-
-#include "common.h"
-#include "sprite.h"
-
-typedef void (*Callback)();
-typedef struct _Sound *Sound;
-
-
-void drawSprites();
-
-Sound createSound(const char *path);
-void soundDestroy(Sound sound);
-void soundPlay(Sound sound, int loop);
-void soundStop(Sound sound);
-
-int keyDown(const char *code);
-int keyWentDown(const char *code);
-int keyWentUp(const char *code);
-
-int mouseDidMove();
-int mouseDown(const char *code);
-int mouseWentDown(const char *code);
-int mouseWentUp(const char *code);
-double mouseX();
-double mouseY();
-
-int mouseIsOver(Sprite sprite);
-int mousePressedOver(Sprite sprite);
-
-
-int worldGetSpriteCount();
-Sprite worldGetSprite(int i);
-
-int worldGetWidth();
-void worldSetWidth(int width);
-
-int worldGetHeight();
-void worldSetHeight(int height);
-
-double worldGetFrameRate();
-void worldSetFrameRate(double frameRate);
-
-double worldGetTimeStep();
-
-int worldGetFrameCount();
-double worldGetSeconds();
-
-void worldSetInit(Callback init);
-void worldSetDraw(Callback draw);
-void worldRun();
-void worldStop();
-
-
-void cameraOn();
-void cameraOff();
-int cameraIsActive();
-
-double cameraMouseX();
-double cameraMouseY();
-
-double cameraGetX();
-void cameraSetX(double x);
-
-double cameraGetY();
-void cameraSetY(double y);
-
-double cameraGetZoom();
-void cameraSetZoom(double zoom);
-
-
-#endif
diff --git a/src/SConstruct b/src/SConstruct
new file mode 100644
index 0000000..59d2bf2
--- /dev/null
+++ b/src/SConstruct
@@ -0,0 +1,94 @@
+
+env = Environment(tools = ['default', 'textfile'])
+
+name = 'helianthus'
+description = 'Helianthus is a library to create small games'
+version = '0.1.0'
+
+
+# user options
+
+opts = Variables(name + '.conf')
+opts.Add(PathVariable('PREFIX', 'Directory to install under', '/usr/local', PathVariable.PathAccept))
+opts.Update(env)
+opts.Save(name + '.conf', env)
+
+
+# config
+
+libs = ['gtk+-3.0', 'glib-2.0', 'cairo', 'SDL2_mixer']
+
+
+# compute build options
+
+flags = ' -O0 -g -lm -Wall -fmessage-length=0 '
+
+
+# files lists
+
+target = name
+
+headers = [
+	'common.h',
+	'drawing.h',
+	'group.h',
+	'sprite.h',
+	'world.h' ]
+
+root_headers = [
+	name + '.h' ]
+
+sources = [
+	'animation.c',
+	'array.c',
+	'collider.c',
+	'common.c',
+	'drawing.c',
+	'group.c',
+	'test.c',
+	'sound.c',
+	'sprite.c',
+	'world.c' ]
+
+
+# build
+
+env.ParseConfig('pkg-config --cflags --libs ' + ' '.join(libs))
+
+static_library = env.StaticLibrary(
+	target = target,
+	source = sources,
+	parse_flags = flags )
+
+shared_library = env.SharedLibrary(
+	target = target,
+	source = sources,
+	parse_flags = flags,
+	SHLIBVERSION = version )
+
+# install
+
+idir_prefix = '$PREFIX'
+idir_lib    = '$PREFIX/lib'
+idir_inc    = '$PREFIX/include'
+env.Export('env idir_prefix idir_lib idir_inc')
+
+pcdict = {
+	'@prefix@'        : idir_prefix,
+	'@exec_prefix@'   : '$${prefix}',
+	'@libdir@'        : ('$${exec_prefix}/lib' if idir_lib == '$PREFIX/lib' else idir_lib),
+	'@includedir@'    : ('$${prefix}/include' if idir_inc == '$PREFIX/include' else idir_inc) + '/' + name,
+	'@NAME@'          : name,
+	'@DESC@'          : description,
+	'@VERSION@'       : version,
+	'@DEPS@'          : ' '.join(libs),
+	'@CONFIG_LIBS@'   : '-l' + name,
+	'@CONFIG_CFLAGS@' : '',
+	}
+pcfile = env.Substfile(name + '.pc.in', SUBST_DICT = pcdict)
+
+env.Install(idir_lib, [static_library, shared_library])
+env.Install(idir_lib + '/pkgconfig', pcfile)
+env.Install(idir_inc + '/' + name + '/' + name, headers)
+env.Install(idir_inc + '/' + name, root_headers)
+env.Alias('install', idir_prefix)
diff --git a/src/animation.c b/src/animation.c
new file mode 100644
index 0000000..068d7c6
--- /dev/null
+++ b/src/animation.c
@@ -0,0 +1,76 @@
+
+#include <glib.h>
+#include <cairo.h>
+
+#include "private.h"
+
+
+static HeliArray cache;
+
+static cairo_status_t read(void *closure, unsigned char *data, unsigned int length) {
+	return fread(data, length, 1, (FILE*)closure)
+		 ? CAIRO_STATUS_SUCCESS : CAIRO_STATUS_READ_ERROR;
+}
+
+static cairo_surface_t* loadFrame(const char *path) {
+	if (!heliStringEndsWithLowcase(path, ".png"))
+		return NULL;
+	FILE *f = fopen(path, "rb");
+	if (f) {
+		cairo_surface_t *frame = cairo_image_surface_create_from_png_stream(&read, f);
+		fclose(f);
+		if (!frame)
+			fprintf(stderr, "helianthus: cannot load PNG content form file: %s\n", path);
+		return frame;
+	}
+	fprintf(stderr, "helianthus: cannot open image file: %s\n", path);
+	return NULL;
+}
+
+static HeliAnimation* load(const char *path) {
+	HeliAnimation *a = calloc(1, sizeof(*a));
+	a->path = heliStringCopy(path);
+	
+	GDir *dir = g_dir_open(path, 0, NULL);
+	if (dir) {
+		while(TRUE) {
+			const char* name = g_dir_read_name(dir);
+			if (!name) break;
+			char *p = heliStringConcat3(path, "/", name);
+			cairo_surface_t *frame = loadFrame(p);
+			free(p);
+			if (frame) heliArrayInsert(&a->frames, -1, frame, (HeliFreeCallback)&cairo_surface_destroy);
+		}
+	} else {
+		cairo_surface_t *frame = loadFrame(path);
+		if (frame) {
+			heliArrayInsert(&a->frames, -1, frame, (HeliFreeCallback)&cairo_surface_destroy);
+		} else {
+			fprintf(stderr, "helianthus: cannot load animation by path: %s\n", path);
+		}
+	}
+	
+	return a;
+}
+
+static void unload(HeliAnimation *a) {
+	assert(!a->refcount);
+	free(a->path);
+	heliArrayDestroy(&a->frames);
+	free(a);
+}
+
+HeliAnimation *heliCreateAnimation(const char *path) {
+	HeliPair *item = heliStringmapGet(&cache, path);
+	if (!item) item = heliStringmapAdd(&cache, path, load(path), (HeliFreeCallback)&unload);
+	HeliAnimation *a = (HeliAnimation*)item->value;
+	++a->refcount;
+	return a;
+}
+
+void heliAnimationUnref(HeliAnimation *a)
+	{ if (--a->refcount <= 0) heliStringmapRemove(&cache, a->path); }
+
+void heliAnimationFinish()
+	{ heliArrayDestroy(&cache); }
+
diff --git a/src/array.c b/src/array.c
new file mode 100644
index 0000000..d6b56d2
--- /dev/null
+++ b/src/array.c
@@ -0,0 +1,133 @@
+
+#include "private.h"
+
+
+void heliPairInit(HeliPair *p) {
+	p->key = p->value = NULL;
+	p->freeKey = p->freeValue = NULL;
+}
+
+void heliPairDestroy(HeliPair *p) {
+	if (p->key && p->freeKey) p->freeKey(p->key);
+	if (p->value && p->freeValue) p->freeKey(p->value);
+	heliPairInit(p);
+}
+
+void heliArrayInit(HeliArray *a) {
+	a->items = NULL;
+	a->count = a->allocated = 0;
+}
+
+void heliArrayDestroy(HeliArray *a) {
+	heliArrayClear(a);
+	free(a->items);
+	heliArrayInit(a);
+}
+
+HeliPair* heliArrayGet(HeliArray *a, int i)
+	{ return i >= 0 && i < a->count ? &a->items[i] : NULL; }
+
+void* heliArrayGetKey(HeliArray *a, int i) {
+	HeliPair *item = heliArrayGet(a, i);
+	return item ? item->key : NULL;
+}
+
+void* heliArrayGetValue(HeliArray *a, int i) {
+	HeliPair *item = heliArrayGet(a, i);
+	return item ? item->value : NULL;
+}
+
+HeliPair* heliArrayInsertPair(HeliArray *a, int i, void *k, void *v, HeliFreeCallback fk, HeliFreeCallback fv) {
+	if (i < 0 || i > a->count)
+		i = a->count;
+	if (a->allocated < a->count + 1) {
+		a->allocated += a->allocated/4 + 32;
+		a->items = realloc(a->items, a->allocated*sizeof(a->items[0]));
+		memset(&a->items[a->count], 0, (a->allocated - a->count)*sizeof(a->items[0]));
+	}
+	if (i < a->count) {
+		memmove(&a->items[i+1], &a->items[i], (a->count-i)*sizeof(a->items[0]));
+		memset(&a->items[i], 0, sizeof(a->items[0]));
+	}
+	++a->count;
+	
+	HeliPair *item = &a->items[i];
+	item->key = k;
+	item->value = v;
+	item->freeKey = fk;
+	item->freeValue = fv;
+	return item;
+}
+
+HeliPair* heliArrayInsert(HeliArray *a, int i, void *v, HeliFreeCallback fv)
+	{ return heliArrayInsertPair(a, i, NULL, v, NULL, fv); }
+
+void heliArrayRemove(HeliArray *a, int i) {
+	if (i < 0 || i >= a->count) return;
+	heliPairDestroy(&a->items[i]);
+	memmove(&a->items[i], &a->items[i+1], (a->count-i-1)*sizeof(a->items[0]));
+	--a->count;
+	memset(&a->items[a->count], 0, sizeof(a->items[0]));
+}
+
+void heliArrayClear(HeliArray *a) {
+	while(a->count > 0)
+		heliArrayRemove(a, a->count-1);
+}
+
+HeliPair* heliStringmapFind(HeliArray *a, const char *k, int *gtOrEqIndex) {
+	int i0 = 0;
+	int i1 = a->count - 1;
+	int cmp = i0 < a->count ? strcmp((char*)a->items[i0].key, k) : -1;
+	if (cmp >= 0) {
+		if (gtOrEqIndex) *gtOrEqIndex = i0;
+		return cmp ? NULL : &a->items[i0];
+	}
+	if (i1 > i0) cmp = strcmp((char*)a->items[i1].key, k);
+	if (cmp < 0) {
+		if (gtOrEqIndex) *gtOrEqIndex = a->count;
+		return NULL;
+	}
+	if (cmp == 0) {
+		if (gtOrEqIndex) *gtOrEqIndex = i1;
+		return &a->items[i1];
+	}
+	
+	while(i0 + 1 < i1) {
+		int i = (i0 + i1)/2;
+		cmp = strcmp((char*)a->items[i].key, k);
+		if (cmp == 0) {
+			if (gtOrEqIndex) *gtOrEqIndex = i;
+			return &a->items[i];
+		}
+		if (cmp < 0) i0 = i; else i1 = i;
+	}
+	if (gtOrEqIndex) *gtOrEqIndex = i1;
+	return NULL;
+}
+
+HeliPair* heliStringmapGet(HeliArray *a, const char *k)
+	{ return heliStringmapFind(a, k, NULL); }
+
+HeliPair* heliStringmapAdd(HeliArray *a, const char *k, void *v, HeliFreeCallback fv) {
+	int i;
+	HeliPair *item = heliStringmapFind(a, k, &i);
+	if (item) {
+		if (item->value && item->freeValue) item->freeValue(item->value);
+		item->value = v;
+		item->freeValue = fv;
+	} else {
+		item = heliArrayInsertPair(a, i, heliStringCopy(k), v, &free, fv);
+	}
+	return item;
+}
+
+int heliStringmapRemove(HeliArray *a, const char *k) {
+	int i;
+	if (heliStringmapFind(a, k, &i)) {
+		heliArrayRemove(a, i);
+		return TRUE;
+	}
+	return FALSE;
+}
+
diff --git a/src/collider.c b/src/collider.c
new file mode 100644
index 0000000..500cc28
--- /dev/null
+++ b/src/collider.c
@@ -0,0 +1,27 @@
+
+#include "private.h"
+
+int heliCheckCollision(HeliCollider *a, HeliCollider *b, double *normX, double *normY) {
+	// corner with side
+	// corner with circle
+	// circle with circle
+	#warning "TODO: heliCheckCollision: not implemented yet"
+	return FALSE;
+}
+
+int heliPointCollision(HeliCollider *c, double x, double y) {
+	x -= c->x;
+	y -= c->y;
+	if (c->type == COLLIDER_CIRCLE) {
+		return x*x + y*y <= c->radius*c->radius;
+	} else
+	if (c->type == COLLIDER_RECTANGLE) {
+		double a = c->rotation*(PI/180);
+		double sn = sin(a);
+		double cn = cos(a);
+		return fabs(x*cn - y*sn) <= c->width*0.5
+			&& fabs(x*sn + y*cn) <= c->height*0.5;
+	}
+	return FALSE;
+}
+
diff --git a/src/common.c b/src/common.c
new file mode 100644
index 0000000..a46a70f
--- /dev/null
+++ b/src/common.c
@@ -0,0 +1,96 @@
+
+#include "private.h"
+
+
+cairo_t *heliCairo;
+
+
+static char *colors[] = {
+	"transparent", "0 0 0 0",
+	
+	"black",       "0 0 0 1",
+	"white",       "1 1 1 1",
+	"gray",        "0.5 0.5 0.5 1",
+	
+	"red",         "1 0 0 1",
+	"green"        "0 1 0 1",
+	"blue"         "0 0 1 1",
+	
+	"yellow",      "1 1 0 1",
+	"magenta",     "1 0 1 1",
+	"cyan",        "0 1 1 1",
+
+	"yellow",      "1 1 0 1",
+	"magenta",     "1 0 1 1",
+	"cyan",        "0 1 1 1",
+	
+	"brown",       "0.5 0.5 0 1",
+};
+
+
+int randomNumber(int min, int max)
+	{ return max <= min ? min : rand()%(max - min + 1) + min; }
+
+double randomFloat()
+	{ return (double)rand()/(double)RAND_MAX; }
+
+
+char* heliStringCopy(const char *x) {
+	int len = strlen(x) + 1;
+	char *cp = malloc(len + 1);
+	memcpy(cp, x, len);
+	return cp;
+}
+
+char* heliStringConcat3(const char *a, const char *b, const char *c) {
+	int la = strlen(a);
+	int lb = strlen(b);
+	int lc = strlen(c);
+	char *s = malloc(la + lb + lc + 1);
+	memcpy(s, a, la);
+	memcpy(s + la, b, lb);
+	memcpy(s + la + lb, c, lc);
+	s[la + lb + lc] = 0;
+	return s;
+}
+
+int heliStringEndsWithLowcase(const char *s, const char *tail) {
+	int ls = strlen(s);
+	int lt = strlen(tail);
+	if (lt > ls) return FALSE;
+	for(int i = 0; i < lt; ++i)
+		if (tolower(s[ls - i]) != tolower(tail[lt - i]))
+			return FALSE;
+	return TRUE;
+}
+
+void heliLowercase(char *x)
+	{ while(*x) { *x = tolower(*x); ++x; } }
+
+
+void heliParseColor(const char *x, double *color) {
+	color[0] = color[1] = color[2] = 0;
+	color[3] = 1;
+	
+	if (*x == '#') {
+		++x;
+		int hex[8] = { 0, 0, 0, 0, 0, 0, 15, 15 };
+		for(int i = 0; *x && i < 8; ++i) {
+			char c = tolower(*x);
+			if (c >= '0' && c <= '9') hex[i] = c - '0';
+			if (c >= 'a' && c <= 'f') hex[i] = c - 'a' + 10;
+		}
+		for(int i = 0; i < 4; ++i)
+			color[i] = (hex[i*2]*16 + hex[i*2 + 1])/255.0;
+	} else
+	if (isalpha(*x)) {
+		int count = (int)(sizeof(colors)/sizeof(*colors)/2);
+		for(int i = 0; i < count; ++i)
+			if (strcmp(x, colors[i*2]) == 0)
+				{ heliParseColor(colors[i*2 + 1], color); return; }
+	} else {
+		sscanf(x, "%lf %lf %lf %lf", &color[0], &color[1], &color[2], &color[3]);
+	}
+}
+
+
diff --git a/src/common.h b/src/common.h
new file mode 100644
index 0000000..1a25cb9
--- /dev/null
+++ b/src/common.h
@@ -0,0 +1,22 @@
+#ifndef HELI_COMMON_H
+#define HELI_COMMON_H
+
+
+#ifndef TRUE
+#define TRUE  1
+#endif
+
+#ifndef FALSE
+#define FALSE 0
+#endif
+
+#ifndef PI
+#define PI 3.14159265358979323846
+#endif
+
+
+int randomNumber(int min, int max);
+double randomFloat();
+
+
+#endif
diff --git a/src/drawing.c b/src/drawing.c
new file mode 100644
index 0000000..ba5e348
--- /dev/null
+++ b/src/drawing.c
@@ -0,0 +1,197 @@
+
+#include <cairo.h>
+
+#include "private.h"
+#include "drawing.h"
+
+static double colorBack[4] = {1, 1, 1, 1};
+static double colorFill[4] = {0.5, 0.5, 0.5, 1};
+static double colorStroke[4] = {0, 0, 0, 1};
+static double lineWidth = 1;
+static double *path;
+static size_t pathSize;
+static size_t pathAllocated;
+
+static HAlign horAlign = HALIGN_LEFT;
+static VAlign vertAlign = VALIGN_TOP;
+static char *font;
+static double fontSize = 24;
+
+
+void background(const char *color)
+	{ heliParseColor(color, colorBack); }
+void fill(const char *color)
+	{ heliParseColor(color, colorFill); }
+void noFill()
+	{ fill("transparent"); }
+void stroke(const char *color)
+	{ heliParseColor(color, colorStroke); }
+void noStroke()
+	{ stroke("transparent"); }
+
+void strokeWeight(double weight)
+	{ lineWidth = weight; }
+
+char* rgba(double r, double g, double b, double a) {
+	static char buf[1024];
+	snprintf(buf, sizeof(buf) - 1, "%f %f %f %f", r, g, b, a);
+	return buf;
+}
+
+char* rgb(double r, double g, double b)
+	{ return rgba(r, g, b, 1); }
+
+void rect(double x, double y, double width, double height) {
+	resetPath();
+	moveTo(x, y);
+	lineTo(x + width, y);
+	lineTo(x + width, y + height);
+	lineTo(x, y + height);
+	closePath();
+}
+
+void line(double x1, double y1, double x2, double y2) {
+	resetPath();
+	moveTo(x1, y1);
+	lineTo(x2, y2);
+	strokePath();
+}
+
+void ellipse(double x, double y, double width, double height) {
+	resetPath();
+	arcPath(x, y, width, height, 0, 360);
+	closePath();
+}
+
+void point(double x, double y)
+	{ ellipse(x - lineWidth*0.25, y - lineWidth*0.25, lineWidth*0.5, lineWidth*0.5); }
+
+void arcPath(double x, double y, double w, double h, double start, double stop) {
+	double step = PI/180;
+	start *= PI/180;
+	stop *= PI/180;
+	if (start < stop) { double s = start; stop = start; start = s; }
+	for(double a = start; a < stop; a += step) {
+		double lx = x + cos(a)*w;
+		double ly = y + sin(a)*h;
+		lineTo(lx, ly);
+	}
+}
+
+void arc(double x, double y, double w, double h, double start, double stop) {
+	resetPath();
+	arcPath(x, y, w, h, start, stop);
+	strokePath();
+}
+
+void regularPolygon(double x, double y, int sides, double size) {
+	resetPath();
+	size *= 0.5;
+	moveTo(x + size, y);
+	for(int i = 1; i < sides; ++i) {
+		double a = i*PI/sides;
+		lineTo(x + size*cos(a), y + size*sin(a));
+	}
+	closePath();
+}
+
+
+void resetPath()
+	{ pathSize = 0; }
+
+static void endPath(int close, int stroke, int fill) {
+	cairo_t *cr = heliCairo;
+	if (cr && pathSize >= 8) {
+		cairo_save(cr);
+		cairo_move_to(cr, path[0], path[1]);
+		for(int i = 2; i < pathSize; i += 2)
+			cairo_line_to(cr, path[i], path[i+1]);
+		if (close)
+			cairo_close_path(cr);
+		if (fill) {
+			cairo_set_source_rgba(cr, colorFill[0], colorFill[1], colorFill[2], colorFill[3]);
+			if (stroke) cairo_fill_preserve(cr); else cairo_fill(cr);
+		}
+		if (stroke) {
+			cairo_set_line_width(cr, lineWidth);
+			cairo_set_source_rgba(cr, colorStroke[0], colorStroke[1], colorStroke[2], colorStroke[3]);
+			cairo_stroke(cr);
+		}
+		cairo_restore(cr);
+	}
+	resetPath();
+}
+
+static void pushPathPoint(double x, double y) {
+	if (pathAllocated < pathSize + 2) {
+		pathAllocated += pathAllocated/4 + 32;
+		path = realloc(path, pathAllocated);
+		memset(&path[pathSize], 0, (pathAllocated - pathSize)*sizeof(*path));
+	}
+	path[pathSize++] = x;
+	path[pathSize++] = y;
+}
+
+void closePath()
+	{ endPath(TRUE, TRUE, TRUE); }
+void strokePath()
+	{ endPath(FALSE, TRUE, FALSE); }
+void lineTo(double x, double y)
+	{ pushPathPoint(x, y); }
+void moveTo(double x, double y)
+	{ resetPath(); lineTo(x, y); }
+
+
+void textAlign(HAlign hor, VAlign vert)
+	{ horAlign = hor; vertAlign = vert; }
+void textFont(const char *f)
+	{ free(font); font = heliStringCopy(f); }
+void textSize(double size)
+	{ fontSize = size; }
+
+void text(const char *text, double x, double y) {
+	resetPath();
+
+	cairo_t *cr = heliCairo;
+	if (!cr) return;
+	cairo_save(cr);
+
+	if (font) cairo_select_font_face(cr, font, CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_NORMAL);
+	cairo_set_font_size(cr, fontSize);
+	
+	cairo_text_extents_t extents;
+	cairo_text_extents(cr, text, &extents);
+	double w = extents.x_bearing + extents.width;
+	double h = extents.y_bearing + extents.height;
+	if (horAlign  == HALIGN_CENTER) x -= w*0.5;
+	if (horAlign  == HALIGN_RIGHT ) x -= w;
+	if (vertAlign == VALIGN_CENTER) y -= h*0.5;
+	if (vertAlign == VALIGN_BOTTOM) y -= h;
+	
+	cairo_set_source_rgba(cr, colorStroke[0], colorStroke[1], colorStroke[2], colorStroke[3]);
+	cairo_move_to(cr, x, y);
+	cairo_show_text(cr, text);
+	
+	cairo_restore(cr);
+}
+
+void heliDrawingClearFrame(cairo_t *cr) {
+	cairo_save(cr);
+	cairo_set_source_rgba(cr, colorBack[0], colorBack[1], colorBack[2], 1);
+	cairo_paint(cr);
+	cairo_restore(cr);
+}
+
+void heliDrawingPrepareFrame() {
+	resetPath();
+	if (heliCairo) heliDrawingClearFrame(heliCairo);
+}
+
+void heliDrawingFinish() {
+	resetPath();
+	free(path);
+	path = NULL;
+	pathAllocated = 0;
+	free(font);
+	font = NULL;
+}
diff --git a/src/drawing.h b/src/drawing.h
new file mode 100644
index 0000000..3fa6f4a
--- /dev/null
+++ b/src/drawing.h
@@ -0,0 +1,48 @@
+#ifndef HELI_DRAWING_H
+#define HELI_DRAWING_H
+
+
+#include "common.h"
+
+typedef enum _HAlign {
+	HALIGN_LEFT,
+	HALIGN_CENTER,
+	HALIGN_RIGHT
+} HAlign;
+
+typedef enum _VAlign {
+	VALIGN_TOP,
+	VALIGN_CENTER,
+	VALIGN_BOTTOM
+} VAlign;
+
+
+void background(const char *color);
+void fill(const char *color);
+void noFill();
+void stroke(const char *color);
+void noStroke();
+void strokeWeight(double weight);
+char* rgb(double r, double g, double b);
+char* rgba(double r, double g, double b, double a);
+void rect(double x, double y, double width, double height);
+void ellipse(double x, double y, double width, double height);
+void text(const char *text, double x, double y);
+void textAlign(HAlign hor, VAlign vert);
+void textFont(const char *font);
+void textSize(double size);
+void arc(double x, double y, double w, double h, double start, double stop);
+void arcPath(double x, double y, double w, double h, double start, double stop);
+void line(double x1, double y1, double x2, double y2);
+void point(double x, double y);
+void regularPolygon(double x, double y, int sides, double size);
+
+void moveTo(double x, double y);
+void lineTo(double x, double y);
+void resetPath();
+void closePath();
+void strokePath();
+
+
+#endif
+
diff --git a/src/group.c b/src/group.c
new file mode 100644
index 0000000..400bffd
--- /dev/null
+++ b/src/group.c
@@ -0,0 +1,209 @@
+
+#include "private.h"
+#include "group.h"
+#include "world.h"
+
+struct _Group {
+	HeliArray sprites;
+};
+
+
+Group createGroup() {
+	Group g = calloc(1, sizeof(*g));
+	return g;
+}
+
+Group createEdgesGroupEx(double x1, double y1, double x2, double y2, double borderWidth) {
+	if (x2 < x1) { double x = x2; x2 = x1; x1 = x; }
+	if (y2 < y1) { double y = y2; y2 = y1; y1 = y; }
+	if (borderWidth < 0.1) borderWidth = 0.1;
+	
+	double b = borderWidth;
+	double w = x2 - x1 + b*2;
+	double h = y2 - y1 + b*2;
+	x1 -= b;
+	y1 -= b;
+	
+	Group g = createGroup();
+	groupAdd(g, createSpriteEx(x1, y1, w, b));
+	groupAdd(g, createSpriteEx(x1, y2, w, b));
+	groupAdd(g, createSpriteEx(x1, y1, b, h));
+	groupAdd(g, createSpriteEx(x2, y1, b, h));
+	return g;
+}
+
+Group createEdgesGroup()
+	{ return createEdgesGroupEx(0, 0, worldGetWidth(), worldGetHeight(), 10); }
+
+
+void groupDestroy(Group group) {
+	heliArrayDestroy(&group->sprites);
+	free(group);
+}
+
+void groupDestroyEx(Group group, int destroySprites) {
+	groupClearEx(group, destroySprites);
+	groupDestroy(group);
+}
+
+void groupAdd(Group group, Sprite sprite) {
+	if (groupContains(group, sprite)) return;
+	heliArrayInsert(&group->sprites, -1, sprite, NULL);
+	heliArrayInsert(heliSpriteGetGroups(sprite), -1, sprite, NULL);
+}
+
+void groupRemove(Group group, Sprite sprite) {
+	for(int i = group->sprites.count-1; i >= 0; --i)
+		if (group->sprites.items[i].value == sprite)
+			heliArrayRemove(&group->sprites, i);
+	HeliArray *groups = heliSpriteGetGroups(sprite);
+	for(int i = groups->count-1; i >= 0; --i)
+		if (groups->items[i].value == group)
+			heliArrayRemove(groups, i);
+}
+
+void groupClearEx(Group group, int destroySprites) {
+	while(groupGetCount(group) > 0) {
+		Sprite s = groupGet(group, 0);
+		groupRemove(group, s);
+		if (destroySprites) spriteDestroy(s);
+	}
+}
+
+void groupClear(Group group)
+	{ groupClearEx(group, FALSE); }
+void groupDestroyEach(Group group)
+	{ groupClearEx(group, TRUE); }
+
+int groupContains(Group group, Sprite sprite) {
+	for(int i = group->sprites.count-1; i >= 0; --i)
+		if (group->sprites.items[i].value == sprite)
+			return TRUE;
+	return FALSE;
+}
+
+int groupGetCount(Group group)
+	{ return group->sprites.count; }
+Sprite groupGet(Group group, int i)
+	{ return (Sprite)heliArrayGetValue(&group->sprites, i); }
+
+int groupOverlap(Group group, Sprite sprite)
+	{ return groupCollideEx(group, sprite, TRUE, TRUE, 0); }
+int groupCollide(Group group, Sprite sprite, double bounciness)
+	{ return groupCollideEx(group, sprite, FALSE, FALSE, bounciness); }
+int groupBounceOff(Group group, Sprite sprite, double bounciness)
+	{ return groupCollideEx(group, sprite, FALSE, TRUE, bounciness); }
+int groupPush(Group group, Sprite sprite, double bounciness)
+	{ return groupCollideEx(group, sprite, TRUE, FALSE, bounciness); }
+int groupCollideEx(Group group, Sprite sprite, int keepVelocityGroup, int keepVelocitySprite, double bounciness) {
+	int result = FALSE;
+	for(int i = 0; i < groupGetCount(group); ++i)
+		if (spriteCollideEx(groupGet(group, i), sprite, keepVelocityGroup, keepVelocitySprite, bounciness))
+			result = TRUE;
+	return result;
+}
+
+int groupOverlapGroup(Group a, Group b)
+	{ return groupCollideGroupEx(a, b, TRUE, TRUE, 0); }
+int groupCollideGroup(Group a, Group b, double bounciness)
+	{ return groupCollideGroupEx(a, b, FALSE, FALSE, bounciness); }
+int groupBounceOffGroup(Group group, Group other, double bounciness)
+	{ return groupCollideGroupEx(group, other, FALSE, TRUE, bounciness); }
+int groupPushGroup(Group group, Group other, double bounciness)
+	{ return groupCollideGroupEx(group, other, TRUE, FALSE, bounciness); }
+int groupCollideGroupEx(Group a, Group b, int keepVelocityA, int keepVelocityB, double bounciness) {
+	int result = FALSE;
+	for(int i = 0; i < groupGetCount(b); ++i)
+		if (groupCollideEx(a, groupGet(b, i), keepVelocityA, keepVelocityB, bounciness))
+			result = TRUE;
+	return result;
+}
+
+double groupGetMinDepth(Group group) {
+	if (groupGetCount(group) <= 0) return 0;
+	double md = spriteGetDepth(groupGet(group, 0));
+	for(int i = 1; i < groupGetCount(group); ++i) {
+		double d = spriteGetDepth(groupGet(group, i));
+		if (d < md) md = d;
+	}
+	return md;
+}
+
+double groupGetMaxDepth(Group group) {
+	if (groupGetCount(group) <= 0) return 0;
+	double md = spriteGetDepth(groupGet(group, 0));
+	for(int i = 1; i < groupGetCount(group); ++i) {
+		double d = spriteGetDepth(groupGet(group, i));
+		if (d > md) md = d;
+	}
+	return md;
+}
+
+
+static void foreachInt(Group group, int value, HeliSpriteEashInt func)
+	{ for(int i = 0; i < groupGetCount(group); ++i) func(groupGet(group, i), value); }
+static void foreachDouble(Group group, double value, HeliSpriteEashDouble func)
+	{ for(int i = 0; i < groupGetCount(group); ++i) func(groupGet(group, i), value); }
+static void foreachString(Group group, const char *value, HeliSpriteEashString func)
+	{ for(int i = 0; i < groupGetCount(group); ++i) func(groupGet(group, i), value); }
+
+
+void groupDestroyTimerEach(Group group, double lifetime)
+	{ foreachDouble(group, lifetime, &spriteDestroyTimer); }
+
+void groupSetVisibleEach(Group group, int visible)
+	{ foreachInt(group, visible, &spriteSetVisible); }
+void groupSetWidthEach(Group group, double width)
+	{ foreachDouble(group, width, &spriteSetWidth); }
+void groupSetHeightEach(Group group, double height)
+	{ foreachDouble(group, height, &spriteSetHeight); }
+void groupSetDepthEach(Group group, double depth)
+	{ foreachDouble(group, depth, &spriteSetDepth); }
+void groupSetVelocityXEach(Group group, double x)
+	{ foreachDouble(group, x, &spriteSetVelocityX); }
+void groupSetVelocityYEach(Group group, double y)
+	{ foreachDouble(group, y, &spriteSetVelocityY); }
+void groupSetRotateToDirectionEach(Group group, int rotateToDirection)
+	{ foreachInt(group, rotateToDirection, &spriteSetRotateToDirection); }
+void groupSetRotationEach(Group group, double rotation)
+	{ foreachDouble(group, rotation, &spriteSetRotation); }
+void groupSetRotationSpeedEach(Group group, double rotationSpeed)
+	{ foreachDouble(group, rotationSpeed, &spriteSetRotationSpeed); }
+void groupSetScaleEach(Group group, double scale)
+	{ foreachDouble(group, scale, &spriteSetScale); }
+void groupSetMirrorXEach(Group group, int mirrorX)
+	{ foreachInt(group, mirrorX, &spriteSetMirrorX); }
+void groupSetMirrorYEach(Group group, int mirrorY)
+	{ foreachInt(group, mirrorY, &spriteSetMirrorY); }
+void groupSetAnimationEach(Group group, const char *path)
+	{ foreachString(group, path, &spriteSetAnimation); }
+void groupSetShapeColorEach(Group group, const char *color)
+	{ foreachString(group, color, &spriteSetShapeColor); }
+void groupSetTintColorEach(Group group, const char *color)
+	{ foreachString(group, color, &spriteSetTintColor); }
+
+void groupPointToEach(Group group, double x, double y) {
+	for(int i = 0; i < groupGetCount(group); ++i)
+		spritePointTo(groupGet(group, i), x, y);
+}
+
+void groupSetSpeedAndDirectionEach(Group group, double speed, double angle) {
+	for(int i = 0; i < groupGetCount(group); ++i)
+		spriteSetSpeedAndDirection(groupGet(group, i), speed, angle);
+}
+
+void groupSetVelocityEach(Group group, double x, double y) {
+	for(int i = 0; i < groupGetCount(group); ++i)
+		spriteSetVelocityXY(groupGet(group, i), x, y);
+}
+
+void groupSetColliderEachEx(Group group, Collider type, double xOffset, double yOffset,
+							double widthOrRadius, double height, double rotationOffset)
+{
+	for(int i = 0; i < groupGetCount(group); ++i)
+		spriteSetColliderEx(groupGet(group, i), type, xOffset, yOffset,
+							widthOrRadius, height, rotationOffset);
+}
+
+void groupSetColliderEach(Group group, Collider type, double xOffset, double yOffset)
+	{ groupSetColliderEachEx(group, type, xOffset, yOffset, -1, -1, 0); }
diff --git a/src/group.h b/src/group.h
new file mode 100644
index 0000000..241577c
--- /dev/null
+++ b/src/group.h
@@ -0,0 +1,68 @@
+#ifndef HELI_GROUP_H
+#define HELI_GROUP_H
+
+
+#include "sprite.h"
+
+
+typedef struct _Group *Group;
+
+
+Group createGroup();
+Group createEdgesGroup();
+Group createEdgesGroupEx(double x1, double y1, double x2, double y2, double borderWidth);
+
+void groupDestroy(Group group);
+void groupDestroyEx(Group group, int destroySprites);
+
+void groupAdd(Group group, Sprite sprite);
+void groupRemove(Group group, Sprite sprite);
+void groupClear(Group group);
+void groupClearEx(Group group, int destroySprites);
+int groupContains(Group group, Sprite sprite);
+int groupGetCount(Group group);
+Sprite groupGet(Group group, int i);
+
+int groupOverlap(Group group, Sprite sprite);
+int groupCollide(Group group, Sprite sprite, double bounciness);
+int groupBounceOff(Group group, Sprite sprite, double bounciness);
+int groupPush(Group group, Sprite sprite, double bounciness);
+int groupCollideEx(Group group, Sprite sprite, int keepVelocityGroup, int keepVelocitySprite, double bounciness);
+
+int groupOverlapGroup(Group a, Group b);
+int groupCollideGroup(Group a, Group b, double bounciness);
+int groupBounceOffGroup(Group group, Group other, double bounciness);
+int groupPushGroup(Group group, Group other, double bounciness);
+int groupCollideGroupEx(Group a, Group b, int keepVelocityA, int keepVelocityB, double bounciness);
+
+double groupGetMinDepth(Group group);
+double groupGetMaxDepth(Group group);
+
+void groupDestroyEach(Group group);
+void groupDestroyTimerEach(Group group, double lifetime);
+
+void groupSetVisibleEach(Group group, int visible);
+void groupSetWidthEach(Group group, double width);
+void groupSetHeightEach(Group group, double height);
+void groupSetDepthEach(Group group, double depth);
+void groupSetVelocityXEach(Group group, double x);
+void groupSetVelocityYEach(Group group, double y);
+void groupSetVelocityEach(Group group, double x, double y);
+void groupSetLifetimeEach(Group group, double lifetime);
+void groupSetRotateToDirectionEach(Group group, int rotateToDirection);
+void groupSetRotationEach(Group group, double rotation);
+void groupSetRotationSpeedEach(Group group, double rotationSpeed);
+void groupSetScaleEach(Group group, double scale);
+void groupSetMirrorXEach(Group group, int mirrorX);
+void groupSetMirrorYEach(Group group, int mirrorY);
+void groupPointToEach(Group group, double x, double y);
+void groupSetSpeedAndDirectionEach(Group group, double speed, double angle);
+void groupSetAnimationEach(Group group, const char *path);
+void groupSetShapeColorEach(Group group, const char *color);
+void groupSetTintColorEach(Group group, const char *color);
+void groupSetColliderEach(Group group, Collider type, double xOffset, double yOffset);
+void groupSetColliderEachEx(Group group, Collider type, double xOffset, double yOffset,
+							double widthOrRadius, double height, double rotationOffset);
+
+
+#endif
diff --git a/src/helianthus.h b/src/helianthus.h
new file mode 100644
index 0000000..9990ca7
--- /dev/null
+++ b/src/helianthus.h
@@ -0,0 +1,12 @@
+#ifndef HELI_HELIANTUS_H
+#define HELI_HELIANTUS_H
+
+
+#include "helianthus/common.h"
+#include "helianthus/world.h"
+#include "helianthus/sprite.h"
+#include "helianthus/group.h"
+#include "helianthus/drawing.h"
+
+
+#endif
diff --git a/src/helianthus.pc.in b/src/helianthus.pc.in
new file mode 100644
index 0000000..f4a75d3
--- /dev/null
+++ b/src/helianthus.pc.in
@@ -0,0 +1,12 @@
+prefix=@prefix@
+exec_prefix=@exec_prefix@
+libdir=@libdir@
+includedir=@includedir@
+
+Name: @NAME@
+Description: @DESC@
+Requires: @DEPS@
+Version: @VERSION@
+Libs: -L${libdir} @CONFIG_LIBS@
+Cflags: @CONFIG_CFLAGS@ -I${includedir}
+
diff --git a/src/private.h b/src/private.h
new file mode 100644
index 0000000..34b7d47
--- /dev/null
+++ b/src/private.h
@@ -0,0 +1,120 @@
+
+#include <assert.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <ctype.h>
+#include <math.h>
+
+#include <cairo.h>
+
+#include "common.h"
+#include "sprite.h"
+
+
+// globals
+
+extern cairo_t *heliCairo;
+
+
+// string
+
+char* heliStringCopy(const char *x);
+char* heliStringConcat3(const char *a, const char *b, const char *c);
+int heliStringEndsWithLowcase(const char *s, const char *tail);
+void heliLowercase(char *x);
+void heliParseColor(const char *x, double *color);
+
+
+// pointer array
+
+typedef void (*HeliFreeCallback)(void*);
+
+typedef struct _HeliPair {
+	void *key;
+	void *value;
+	HeliFreeCallback freeKey;
+	HeliFreeCallback freeValue;
+} HeliPair;
+
+typedef struct _HeliArray {
+	HeliPair *items;
+	int count;
+	int allocated;
+} HeliArray;
+
+void heliPairInit(HeliPair *p);
+void heliPairDestroy(HeliPair *p);
+
+void heliArrayInit(HeliArray *a);
+void heliArrayClear(HeliArray *a);
+void heliArrayDestroy(HeliArray *a);
+HeliPair* heliArrayGet(HeliArray *a, int i);
+void* heliArrayGetKey(HeliArray *a, int i);
+void* heliArrayGetValue(HeliArray *a, int i);
+HeliPair* heliArrayInsert(HeliArray *a, int i, void *v, HeliFreeCallback fv);
+HeliPair* heliArrayInsertPair(HeliArray *a, int i, void *k, void *v, HeliFreeCallback fk, HeliFreeCallback fv);
+void heliArrayRemove(HeliArray *a, int i);
+
+HeliPair* heliStringmapFind(HeliArray *a, const char *k, int *gtOrEqIndex);
+HeliPair* heliStringmapGet(HeliArray *a, const char *k);
+HeliPair* heliStringmapAdd(HeliArray *a, const char *k, void *v, HeliFreeCallback fv);
+int heliStringmapRemove(HeliArray *a, const char *k);
+
+
+// animation
+
+typedef struct _HeliAnimation {
+	char *path;
+	HeliArray frames;
+	int refcount;
+} HeliAnimation;
+
+HeliAnimation *heliCreateAnimation(const char *path);
+void heliAnimationUnref(HeliAnimation *a);
+void heliAnimationFinish();
+
+
+// collider
+
+typedef struct _HeliCollider {
+	Collider type;
+	double x;
+	double y;
+	double radius;
+	double width;
+	double height;
+	double rotation;
+} HeliCollider;
+
+int heliCheckCollision(HeliCollider *a, HeliCollider *b, double *normX, double *normY);
+int heliPointCollision(HeliCollider *c, double x, double y);
+
+
+// sprite
+
+typedef void (*HeliSpriteEashInt)(Sprite, int);
+typedef void (*HeliSpriteEashDouble)(Sprite, double);
+typedef void (*HeliSpriteEashString)(Sprite, const char*);
+HeliArray* heliSpriteGetGroups(Sprite sprite);
+void heliSpriteUpdate(double dt);
+void heliSpriteFinish();
+
+
+// drawing
+
+void heliDrawingClearFrame(cairo_t *cr);
+void heliDrawingPrepareFrame();
+void heliDrawingFinish();
+
+
+// sound
+
+void heliSoundUpdate();
+void heliSoundFinish();
+
+
+// test
+
+void heliDoTests();
+
diff --git a/src/sound.c b/src/sound.c
new file mode 100644
index 0000000..aa36d92
--- /dev/null
+++ b/src/sound.c
@@ -0,0 +1,163 @@
+
+#include <glib.h>
+
+#include <SDL.h>
+#include <SDL_mixer.h>
+
+#include "private.h"
+#include "world.h"
+
+
+#define HELI_SOUND_CHANNELS 64
+
+
+typedef struct _HeliSoundInstance {
+	char *path;
+	Mix_Chunk *chunk;
+	int refcount;
+} HeliSoundInstance;
+
+typedef struct _HeliSoundTrashItem {
+	Mix_Chunk *chunk;
+	gint64 time;
+} HeliSoundTrashItem;
+
+struct _Sound {
+	HeliSoundInstance *instance;
+};
+
+
+static int initialized;
+static int ready;
+
+static HeliArray cache;
+static Sound channels[HELI_SOUND_CHANNELS];
+
+static HeliSoundTrashItem *trash;
+static size_t trashSize;
+
+
+static void trashAdd(Mix_Chunk *chunk) {
+	if (!chunk) return;
+	
+	gint64 time = g_get_monotonic_time() + 1000000;
+	for(int i = 0; i < trashSize; ++i)
+		if (!trash[i].chunk) 
+			{ trash[i].chunk = chunk; trash[i].time = time; return; }
+	
+	size_t prevSize = trashSize;
+	trashSize += trashSize/4 + 32;
+	trash = realloc(trash, trashSize);
+	memset(&trash[prevSize], 0, (trashSize - prevSize)*sizeof(*trash));
+	
+	trash[prevSize].chunk = chunk;
+	trash[prevSize].time = time;
+}
+
+static void trashProcess() {
+	gint64 time = g_get_monotonic_time();
+	for(int i = 0; i < trashSize; ++i)
+		if (trash[i].chunk && trash[i].time <= time)
+			{ Mix_FreeChunk(trash[i].chunk); trash[i].chunk = NULL; }
+}
+
+static void trashDestroy() {
+	for(int i = 0; i < trashSize; ++i)
+		if (trash[i].chunk) Mix_FreeChunk(trash[i].chunk);
+	trashSize = 0;
+	free(trash);
+	trash = NULL;
+}
+
+
+static void init() {
+	if (initialized) return;
+	if (SDL_Init(SDL_INIT_AUDIO) == 0) {
+		int loaded = Mix_Init(MIX_INIT_OGG | MIX_INIT_FLAC | MIX_INIT_MP3);
+		if (!(loaded & MIX_INIT_OGG )) fprintf(stderr, "helianthus: cannot initialize OGG  support\n");
+		if (!(loaded & MIX_INIT_FLAC)) fprintf(stderr, "helianthus: cannot initialize FLAC support\n");
+		if (!(loaded & MIX_INIT_MP3 )) fprintf(stderr, "helianthus: cannot initialize MP3  support\n");
+		ready = Mix_OpenAudio(44100, MIX_DEFAULT_FORMAT, 2, 1024) == 0;
+		if (!ready) fprintf(stderr, "helianthus: cannot open audio device\n");
+	}
+	initialized = TRUE;
+}
+
+static void deinit() {
+	if (!initialized) return;
+	heliArrayDestroy(&cache);
+	if (ready) Mix_CloseAudio();
+	trashDestroy();
+	Mix_Quit();
+	SDL_Quit();
+	for(int i = 0; i < HELI_SOUND_CHANNELS; ++i) channels[i] = NULL;
+	ready = FALSE;
+	initialized = FALSE;
+}
+
+
+static HeliSoundInstance* load(const char *path) {
+	HeliSoundInstance *s = calloc(1, sizeof(*s));
+	s->path = heliStringCopy(path);
+	if (ready) {
+		s->chunk = Mix_LoadWAV(path);
+		if (!s->chunk)
+			fprintf(stderr, "helianthus: cannot load sound file: %s\n", path);
+	}
+	return s;
+}
+
+static void unload(HeliSoundInstance *s) {
+	assert(!s->refcount);
+	free(s->path);
+	trashAdd(s->chunk);
+	free(s);
+}
+
+
+Sound createSound(const char *path) {
+	init();
+	HeliPair *item = heliStringmapGet(&cache, path);
+	if (!item) item = heliStringmapAdd(&cache, path, load(path), (HeliFreeCallback)&unload);
+	HeliSoundInstance *s = (HeliSoundInstance*)item->value;
+	++s->refcount;
+	
+	Sound sound = calloc(1, sizeof(*sound));
+	sound->instance = s;
+	return sound;
+}
+
+void soundDestroy(Sound sound) {
+	soundStop(sound);
+	if (--sound->instance->refcount <= 0)
+		heliStringmapRemove(&cache, sound->instance->path);
+}
+
+
+void soundPlay(Sound sound, int loop) {
+	if (!ready) return;
+	if (sound->instance->chunk) {
+		int channel = Mix_PlayChannel(-1, sound->instance->chunk, loop ? -1 : 0);
+		assert(channel < HELI_SOUND_CHANNELS);
+		if (channel >= 0 && channel < HELI_SOUND_CHANNELS)
+			channels[channel] = sound;
+	}
+}
+
+void soundStop(Sound sound) {
+	for(int i = 0; i < HELI_SOUND_CHANNELS; ++i) {
+		if (channels[i] == sound) {
+			Mix_Pause(i);
+			Mix_HaltChannel(i);
+			channels[i] = NULL;
+		}
+	}
+}
+
+
+void heliSoundUpdate()
+	{ trashProcess(); }
+
+void heliSoundFinish()
+	{ deinit(); }
+
diff --git a/src/sprite.c b/src/sprite.c
new file mode 100644
index 0000000..eb14663
--- /dev/null
+++ b/src/sprite.c
@@ -0,0 +1,441 @@
+
+#include <cairo.h>
+
+#include "private.h"
+
+#include "sprite.h"
+#include "world.h"
+#include "group.h"
+
+struct _Sprite {
+	double x;
+	double y;
+	double rotation;
+	double width;
+	double height;
+	double scale;
+	
+	double vx;
+	double vy;
+	double rotationSpeed;
+	
+	HeliCollider collider;
+	double bounciness;
+	
+	int rotateToDirection;
+	int mirrorX;
+	int mirrorY;
+	double depth;
+	double lifeTime;
+	int visible;
+	int debug;
+	
+	double shapeColor[4];
+	double tintColor[4];
+	
+	int playing;
+	int frame;
+	
+	HeliArray groups;
+	
+	HeliAnimation *animation;
+};
+
+static HeliArray sprites;
+static HeliArray spritesSorted;
+
+
+static void prepareCollider(Sprite sprite, HeliCollider *collider) {
+	collider->type = sprite->collider.type;
+	collider->x = sprite->collider.x + sprite->x;
+	collider->y = sprite->collider.y + sprite->y;
+	collider->width = sprite->collider.width >= 0 ? sprite->collider.width : sprite->width;
+	collider->height = sprite->collider.height >= 0 ? sprite->collider.height : sprite->height;
+	collider->radius = sprite->collider.radius >= 0 ? sprite->collider.radius : collider->width;
+	collider->rotation = sprite->collider.rotation + sprite->rotation;
+}
+
+
+
+Sprite createSpriteEx(double x, double y, double width, double height) {
+	Sprite s = calloc(1, sizeof(*s));
+	s->x = x;
+	s->y = y;
+	s->width = width;
+	s->height = height;
+	
+	s->scale = 1;
+	s->collider.type = COLLIDER_RECTANGLE;
+	s->collider.width = s->collider.height = s->collider.radius = -1;
+	
+	s->mirrorX = 1;
+	s->mirrorY = 1;
+	s->lifeTime = -1;
+	s->visible = TRUE;
+	
+	s->shapeColor[0] = s->shapeColor[1] = s->shapeColor[2] = 0.5;
+	s->shapeColor[3] = 1;
+	s->tintColor[0] = s->tintColor[1] = s->tintColor[2] = s->tintColor[3] = 1;
+	
+	heliArrayInsert(&sprites, -1, s, NULL);
+	heliArrayInsert(&spritesSorted, -1, s, NULL);
+	
+	return s;
+}
+
+Sprite createSprite(double x, double y)
+	{ return createSpriteEx(x, y, 100, 100); }
+
+void spriteDestroy(Sprite sprite) {
+	while(sprite->groups.count > 0)
+		groupRemove((Group)sprite->groups.items[0].value, sprite);
+	for(int i = 0; i < sprites.count; ++i)
+		if (sprites.items[i].value == sprite)
+			{ heliArrayRemove(&sprites, i); break; }
+	for(int i = 0; i < spritesSorted.count; ++i)
+		if (spritesSorted.items[i].value == sprite)
+			{ heliArrayRemove(&spritesSorted, i); break; }
+	if (sprite->animation)
+		heliAnimationUnref(sprite->animation);
+	free(sprite);
+}
+
+void spriteDestroyTimer(Sprite sprite, double lifeTime) {
+	if (lifeTime <= 0) { spriteDestroy(sprite); return; }
+	sprite->lifeTime = lifeTime;
+}
+
+double spriteGetX(Sprite sprite) { return sprite->x; }
+void spriteSetX(Sprite sprite, double x) { sprite->x = x; }
+
+double spriteGetY(Sprite sprite) { return sprite->y; }
+void spriteSetY(Sprite sprite, double y) { sprite->y = y; }
+
+double spriteGetVelocityX(Sprite sprite) { return sprite->vx; }
+void spriteSetVelocityX(Sprite sprite, double x)
+	{ spriteSetVelocityXY(sprite, x, sprite->vy); }
+
+double spriteGetVelocityY(Sprite sprite) { return sprite->vy; }
+void spriteSetVelocityY(Sprite sprite, double y)
+	{ spriteSetVelocityXY(sprite, sprite->vx, y); }
+
+double spriteGetScale(Sprite sprite) { return sprite->scale; }
+void spriteSetScale(Sprite sprite, double scale) { sprite->scale = scale; }
+
+double spriteGetWidth(Sprite sprite) { return sprite->width; }
+void spriteSetWidth(Sprite sprite, double width)
+	{ sprite->width = width > 0 ? width : 0; }
+
+double spriteGetHeight(Sprite sprite) { return sprite->height; }
+void spriteSetHeight(Sprite sprite, double height)
+	{ sprite->height = height > 0 ? height : 0; }
+
+int spriteGetRotateToDirection(Sprite sprite) { return sprite->rotateToDirection; }
+void spriteSetRotateToDirection(Sprite sprite, int rotateToDirection) {
+	if (rotateToDirection) {
+		sprite->rotateToDirection = TRUE;
+		sprite->rotation = spriteGetDirection(sprite);
+	} else {
+		sprite->rotateToDirection = FALSE;
+	}
+}
+
+double spriteGetRotation(Sprite sprite) { return sprite->rotation; }
+void spriteSetRotation(Sprite sprite, double rotation)
+	{ if (!sprite->rotateToDirection) sprite->rotation = rotation; }
+
+double spriteGetRotationSpeed(Sprite sprite) { return sprite->rotationSpeed; }
+void spriteSetRotationSpeed(Sprite sprite, double rotationSpeed)
+	{ sprite->rotationSpeed = rotationSpeed; }
+
+int spriteGetMirrorX(Sprite sprite) { return sprite->mirrorX; }
+void spriteSetMirrorX(Sprite sprite, int mirrorX)
+	{ sprite->mirrorX = mirrorX < 0 ? -1 : 1; }
+
+int spriteGetMirrorY(Sprite sprite) { return sprite->mirrorY; }
+void spriteSetMirrorY(Sprite sprite, int mirrorY)
+	{ sprite->mirrorY = mirrorY < 0 ? -1 : 1; }
+
+double spriteGetDepth(Sprite sprite) { return sprite->depth; }
+void spriteSetDepth(Sprite sprite, double depth)
+	{ sprite->depth = depth; }
+
+int spriteGetVisible(Sprite sprite) { return sprite->visible; }
+void spriteSetVisible(Sprite sprite, int visible)
+	{ sprite->visible = visible != FALSE; }
+
+int spriteGetDebug(Sprite sprite) { return sprite->debug; }
+void spriteSetDebug(Sprite sprite, int debug)
+	{ sprite->debug = debug != FALSE; }
+
+int spriteOverlap(Sprite a, Sprite b)
+	{ return spriteCollideEx(a, b, TRUE, TRUE, 0); }
+int spriteCollide(Sprite a, Sprite b, double bounciness)
+	{ return spriteCollideEx(a, b, FALSE, FALSE, bounciness); }
+int spriteBounceOff(Sprite sprite, Sprite other, double bounciness)
+	{ return spriteCollideEx(sprite, other, FALSE, TRUE, bounciness); }
+int spritePush(Sprite sprite, Sprite other, double bounciness)
+	{ return spriteCollideEx(sprite, other, TRUE, FALSE, bounciness); }
+
+int spriteCollideEx(Sprite a, Sprite b, int keepVelocityA, int keepVelocityB, double bounciness) {
+	#warning "TODO: spriteCollision: not implemented yet"
+	return FALSE;
+}
+
+
+double spriteGetBounciness(Sprite sprite) { return sprite->bounciness; }
+void spriteSetBounciness(Sprite sprite, double bounciness)
+	{ sprite->bounciness = bounciness > 0 ? bounciness : 0; }
+
+void spriteSetColliderEx(Sprite sprite, Collider type, double xOffset, double yOffset,
+						 double widthOrRadius, double height, double rotationOffset)
+{
+	sprite->collider.type = type;
+	sprite->collider.x = xOffset;
+	sprite->collider.y = yOffset;
+	sprite->collider.width = sprite->collider.radius = widthOrRadius;
+	sprite->collider.height = height;
+	sprite->collider.rotation = rotationOffset;
+}
+
+void spriteSetCollider(Sprite sprite, Collider type, double xOffset, double yOffset)
+	{ spriteSetColliderEx(sprite, type, xOffset, yOffset, -1, -1, 0); }
+
+void spriteSetAnimation(Sprite sprite, const char *path) {
+	HeliAnimation *prev = sprite->animation;
+	sprite->animation = heliCreateAnimation(path);
+	if (prev) heliAnimationUnref(prev);
+	spriteSetFrame(sprite, sprite->frame);
+}
+
+void spritePlay(Sprite sprite) { sprite->playing = TRUE; }
+void spritePause(Sprite sprite) { sprite->playing = FALSE; }
+void spriteNextFrame(Sprite sprite) { spriteSetFrame(sprite, sprite->frame + 1); }
+
+void spriteSetFrame(Sprite sprite, int frame) {
+	sprite->frame = frame >= 0 && sprite->animation && sprite->animation->frames.count > 0
+				  ? frame % sprite->animation->frames.count : 0;
+}
+
+void spriteSetShapeColor(Sprite sprite, const char *color)
+	{ heliParseColor(color, sprite->shapeColor); }
+void spriteSetTintColor(Sprite sprite, const char *color)
+	{ heliParseColor(color, sprite->tintColor); }
+
+void spriteSetVelocityXY(Sprite sprite, double x, double y) {
+	sprite->vx = x;
+	sprite->vy = y;
+	if (sprite->rotateToDirection)
+		sprite->rotation = spriteGetDirection(sprite);
+}
+
+void spriteSetSpeedAndDirection(Sprite sprite, double speed, double angle) {
+	double a = angle*(PI/180);
+	spriteSetVelocityXY(sprite, cos(a)*speed, sin(a)*speed);
+}
+
+double spriteGetSpeed(Sprite sprite)
+	{ return sqrt(sprite->vx*sprite->vx + sprite->vy*sprite->vy); }
+double spriteGetDirection(Sprite sprite) {
+	return fabs(sprite->vx) > 1e-6 || fabs(sprite->vy) > 1e-6
+	     ? atan2(sprite->vy, sprite->vx)*(180/PI) : 0;
+}
+void spritePointTo(Sprite sprite, double x, double y)
+	{ spriteSetRotation( sprite, atan2(y - sprite->y, x - sprite->x)*(180/PI) ); }
+
+double spriteGetScaledWidth(Sprite sprite)
+	{ return sprite->width * sprite->scale; }
+double spriteGetScaledHeight(Sprite sprite)
+	{ return sprite->height * sprite->scale; }
+
+
+
+int worldGetSpriteCount()
+	{ return sprites.count; }
+
+Sprite worldGetSprite(int i)
+	{ return (Sprite)heliArrayGetValue(&sprites, i); }
+
+
+static void drawSpriteDebug(cairo_t *cr, Sprite s) {
+	cairo_save(cr);
+	cairo_set_line_width(cr, 0.5);
+	cairo_translate(cr, s->x, s->y);
+	cairo_rotate(cr, s->rotation*(PI/180));
+	cairo_scale(cr, s->scale*s->mirrorX, s->scale*s->mirrorY);
+	
+	double hw = s->width*0.5;
+	double hh = s->height*0.5;
+
+	cairo_set_source_rgba(cr, 0, 0, 0, 0.75);
+	cairo_move_to(cr, -hw, -hh);
+	cairo_line_to(cr,  hw, -hh);
+	cairo_line_to(cr,  hw,  hh);
+	cairo_line_to(cr, -hw,  hh);
+	cairo_close_path(cr);
+	cairo_stroke(cr);
+
+	cairo_move_to(cr, -hw*0.25, 0);
+	cairo_line_to(cr,  hw*0.25, 0);
+	cairo_move_to(cr, 0, -hh*0.25);
+	cairo_line_to(cr, 0,  hh*0.25);
+	cairo_stroke(cr);
+	
+	char buf[1024];
+	snprintf(buf, sizeof(buf)-1, "%lf", s->depth);
+	
+	double s1 = hw*0.25;
+	double s2 = hh*0.5;
+	cairo_set_font_size(cr, s1 < s2 ? s1 : s2);
+
+	cairo_move_to(cr, -hw*0.9, -hh*0.5);
+	cairo_show_text(cr, buf);
+
+	cairo_restore(cr);
+}
+
+static void drawSprite(cairo_t *cr, Sprite s) {
+	cairo_save(cr);
+	cairo_translate(cr, s->x, s->y);
+	cairo_rotate(cr, s->rotation*(PI/180));
+	cairo_scale(cr, s->scale*s->mirrorX, s->scale*s->mirrorY);
+	
+	double hw = s->width*0.5;
+	double hh = s->height*0.5;
+	
+	cairo_surface_t *frame = s->animation
+						   ? (cairo_surface_t*)heliArrayGetValue(&s->animation->frames, s->frame) : NULL;
+
+	double a = s->tintColor[3];
+	int tint = fabs(s->tintColor[0] - 1) > 1e-5
+			|| fabs(s->tintColor[1] - 1) > 1e-5
+			|| fabs(s->tintColor[2] - 1) > 1e-5;
+	int alpha = fabs(a) > 1e-5;
+	int visible = fabs(a) > 1e-5;
+	
+	if (visible) {
+		if (tint) cairo_push_group(cr);
+		
+		if (frame) {
+			// image
+			double ihw = cairo_image_surface_get_width(frame)*0.5;
+			double ihh = cairo_image_surface_get_height(frame)*0.5;
+			if (ihw > 1e-6 && ihh > 1e-6) {
+				cairo_save(cr);
+				cairo_scale(cr, hw/ihw, hh/ihh);
+				cairo_set_source_surface(cr, frame, -ihw, -ihh);
+				if (alpha) cairo_paint_with_alpha(cr, a); else cairo_paint(cr);
+				cairo_restore(cr);
+			}
+		} else {
+			// rectangle
+			cairo_set_source_rgba(cr, s->shapeColor[0], s->shapeColor[1], s->shapeColor[2], s->shapeColor[3]*a);
+			cairo_move_to(cr, -hw, -hh);
+			cairo_line_to(cr,  hw, -hh);
+			cairo_line_to(cr,  hw,  hh);
+			cairo_line_to(cr, -hw,  hh);
+			cairo_close_path(cr);
+			cairo_fill(cr);
+		}
+		
+		if (tint) {
+			cairo_pattern_t *spriteGroup = cairo_pop_group(cr);
+			cairo_push_group(cr);
+			cairo_set_source(cr, spriteGroup);
+			cairo_paint(cr);
+			cairo_set_source_rgba(cr, s->tintColor[0], s->tintColor[1], s->tintColor[2], 1);
+			cairo_set_operator(cr, CAIRO_OPERATOR_MULTIPLY);
+			cairo_mask(cr, spriteGroup);
+			cairo_pop_group_to_source(cr);
+			cairo_paint(cr);
+			cairo_pattern_destroy(spriteGroup);
+		}
+	}
+	
+	cairo_restore(cr);
+}
+
+void drawSprites() {
+	// sort
+	int found = TRUE;
+	while(found) {
+		found = FALSE;
+		// forward
+		for(int i = 1; i < spritesSorted.count; ++i) {
+			if ( ((Sprite)spritesSorted.items[i-1].value)->depth
+			   < ((Sprite)spritesSorted.items[i  ].value)->depth )
+			{
+				void *x = spritesSorted.items[i].value;
+				spritesSorted.items[i].value = spritesSorted.items[i-1].value;
+				spritesSorted.items[i-1].value = x;
+				found = TRUE;
+			}
+		}
+		if (!found) break;
+		// backward
+		found = FALSE;
+		for(int i = spritesSorted.count - 1; i > 0; --i) {
+			if ( ((Sprite)spritesSorted.items[i-1].value)->depth
+			   < ((Sprite)spritesSorted.items[i  ].value)->depth )
+			{
+				void *x = spritesSorted.items[i].value;
+				spritesSorted.items[i].value = spritesSorted.items[i-1].value;
+				spritesSorted.items[i-1].value = x;
+				found = TRUE;
+			}
+		}
+	}
+	
+	if (heliCairo) {
+		// draw
+		for(int i = 0; i < spritesSorted.count; ++i) {
+			Sprite s = (Sprite)(spritesSorted.items[i].value);
+			if (s->visible) drawSprite(heliCairo, s);
+		}
+		// draw debug marks
+		for(int i = 0; i < spritesSorted.count; ++i) {
+			Sprite s = (Sprite)(spritesSorted.items[i].value);
+			if (s->debug) drawSpriteDebug(heliCairo, s);
+		}
+	}
+}
+
+int mouseIsOver(Sprite sprite) {
+	HeliCollider collider;
+	prepareCollider(sprite, &collider);
+	return heliPointCollision(&collider, mouseX(), mouseY());
+}
+
+void heliSpriteUpdate(double dt) {
+	// auto-remove
+	for(int i = sprites.count - 1; i > 0; --i) {
+		Sprite s = (Sprite)sprites.items[i].value;
+		if (s->lifeTime >= 0) {
+			s->lifeTime -= dt;
+			if (s->lifeTime <= 1e-5)
+				spriteDestroy(s);
+		}
+	}
+	
+	// update
+	for(int i = 0; i < sprites.count; ++i) {
+		Sprite s = (Sprite)sprites.items[i].value;
+		s->x += s->vx*dt;
+		s->y += s->vy*dt;
+		if (!s->rotateToDirection)
+			s->rotation += s->rotationSpeed*dt;
+		if (s->playing) spriteNextFrame(s);
+	}
+}
+
+HeliArray* heliSpriteGetGroups(Sprite sprite)
+	{ return &sprite->groups; }
+
+void heliSpriteFinish() {
+	while(worldGetSpriteCount())
+		{ spriteDestroy(worldGetSprite(0)); }
+	heliArrayDestroy(&sprites);
+	heliArrayDestroy(&spritesSorted);
+}
+
+
diff --git a/src/sprite.h b/src/sprite.h
new file mode 100644
index 0000000..aa5f28c
--- /dev/null
+++ b/src/sprite.h
@@ -0,0 +1,97 @@
+#ifndef HELI_SPRITE_H
+#define HELI_SPRITE_H
+
+
+#include "common.h"
+
+typedef struct _Sprite *Sprite;
+
+
+typedef enum _Collider {
+	COLLIDER_RECTANGLE,
+	COLLIDER_CIRCLE
+} Collider;
+
+Sprite createSprite(double x, double y);
+Sprite createSpriteEx(double x, double y, double width, double height);
+
+void spriteDestroy(Sprite sprite);
+void spriteDestroyTimer(Sprite sprite, double lifetime);
+
+double spriteGetX(Sprite sprite);
+void spriteSetX(Sprite sprite, double x);
+
+double spriteGetY(Sprite sprite);
+void spriteSetY(Sprite sprite, double y);
+
+double spriteGetVelocityX(Sprite sprite);
+void spriteSetVelocityX(Sprite sprite, double x);
+
+double spriteGetVelocityY(Sprite sprite);
+void spriteSetVelocityY(Sprite sprite, double y);
+
+double spriteGetScale(Sprite sprite);
+void spriteSetScale(Sprite sprite, double scale);
+
+double spriteGetWidth(Sprite sprite);
+void spriteSetWidth(Sprite sprite, double width);
+
+double spriteGetHeight(Sprite sprite);
+void spriteSetHeight(Sprite sprite, double height);
+
+int spriteGetRotateToDirection(Sprite sprite);
+void spriteSetRotateToDirection(Sprite sprite, int rotateToDirection);
+
+double spriteGetRotation(Sprite sprite);
+void spriteSetRotation(Sprite sprite, double rotation);
+
+double spriteGetRotationSpeed(Sprite sprite);
+void spriteSetRotationSpeed(Sprite sprite, double rotationSpeed);
+
+int spriteGetMirrorX(Sprite sprite);
+void spriteSetMirrorX(Sprite sprite, int mirrorX);
+
+int spriteGetMirrorY(Sprite sprite);
+void spriteSetMirrorY(Sprite sprite, int mirrorY);
+
+double spriteGetDepth(Sprite sprite);
+void spriteSetDepth(Sprite sprite, double depth);
+
+int spriteGetVisible(Sprite sprite);
+void spriteSetVisible(Sprite sprite, int visible);
+
+int spriteGetDebug(Sprite sprite);
+void spriteSetDebug(Sprite sprite, int debug);
+
+int spriteOverlap(Sprite a, Sprite b);
+int spriteCollide(Sprite a, Sprite b, double bounciness);
+int spriteBounceOff(Sprite sprite, Sprite other, double bounciness);
+int spritePush(Sprite sprite, Sprite other, double bounciness);
+int spriteCollideEx(Sprite a, Sprite b, int keepVelocityA, int keepVelocityB, double bounciness);
+
+double spriteGetBounciness(Sprite sprite);
+void spriteSetBounciness(Sprite sprite, double bounciness);
+
+void spriteSetCollider(Sprite sprite, Collider type, double xOffset, double yOffset);
+void spriteSetColliderEx(Sprite sprite, Collider type, double xOffset, double yOffset,
+						 double widthOrRadius, double height, double rotationOffset);
+
+void spriteSetAnimation(Sprite sprite, const char *path);
+void spritePlay(Sprite sprite);
+void spritePause(Sprite sprite);
+void spriteNextFrame(Sprite sprite);
+void spriteSetFrame(Sprite sprite, int frame);
+void spriteSetShapeColor(Sprite sprite, const char *color);
+void spriteSetTintColor(Sprite sprite, const char *color);
+
+void spriteSetVelocityXY(Sprite sprite, double x, double y);
+void spriteSetSpeedAndDirection(Sprite sprite, double speed, double angle);
+double spriteGetSpeed(Sprite sprite);
+double spriteGetDirection(Sprite sprite);
+void spritePointTo(Sprite sprite, double x, double y);
+
+double spriteGetScaledWidth(Sprite sprite);
+double spriteGetScaledHeight(Sprite sprite);
+
+
+#endif
diff --git a/src/test.c b/src/test.c
new file mode 100644
index 0000000..713f2cd
--- /dev/null
+++ b/src/test.c
@@ -0,0 +1,60 @@
+
+#include "private.h"
+
+//#define HELI_DO_TESTS
+
+#ifndef HELI_DO_TESTS
+void heliDoTests() { }
+#else
+
+
+static printStringset(HeliArray *a) {
+	for(int i = 0; i < a->count; ++i)
+		printf("  %s\n", (const char*)a->items[i].key);
+}
+
+static void testStringSet() {
+	printf("-- testStringSet\n");
+	
+	static char *strings[] = {
+		"hello",
+		"apple",
+		"orange",
+		"pineapple",
+		"potato",
+		"carrot",
+		"grape",
+		"cucumber"
+	};
+	
+	HeliArray a = {};
+	for(int i = 0; i < (int)(sizeof(strings)/sizeof(*strings)); ++i)
+		heliStringmapAdd(&a, strings[i], NULL, NULL);
+	
+	printf("  fill:\n");
+	printStringset(&a);
+	
+	printf("\n -remove %s:\n", "hello");
+	heliStringmapRemove(&a, "hello");
+	printStringset(&a);
+
+	printf("\n -remove %s:\n", "apple");
+	heliStringmapRemove(&a, "apple");
+	printStringset(&a);
+	
+	printf("\n -remove %s:\n", "potato");
+	heliStringmapRemove(&a, "potato");
+	printStringset(&a);
+	
+	heliArrayDestroy(&a);
+
+	printf("-- end\n");
+}
+
+void heliDoTests() {
+	printf("---- doTests\n");
+	testStringSet();
+	printf("---- end\n");
+}
+
+#endif
diff --git a/src/world.c b/src/world.c
new file mode 100644
index 0000000..a7b9896
--- /dev/null
+++ b/src/world.c
@@ -0,0 +1,322 @@
+
+#include <glib.h>
+#include <gtk/gtk.h>
+#include <gdk/gdk.h>
+
+#include "private.h"
+
+#include "world.h"
+
+
+static GtkWidget *window;
+
+static int started;
+static int stopped;
+static unsigned long long frameCount;
+static gint64 startTime;
+static gint64 currentTime;
+
+static Callback initCallback;
+static Callback drawCallback;
+
+static cairo_surface_t *cairoSurface;
+static int width = 400;
+static int height = 400;
+static double frameRate = 30;
+
+static int cameraEnabled;
+static double cameraX;
+static double cameraY;
+static double cameraZoom = 1;
+
+static HeliArray keysPressed;
+static HeliArray keysPressedInFrame;
+static HeliArray keysReleasedInFrame;
+static HeliArray buttonsPressed;
+static HeliArray buttonsPressedInFrame;
+static HeliArray buttonsReleasedInFrame;
+
+static int mouseMovedInFrame;
+static double _mouseX;
+static double _mouseY;
+
+static char* buttonNames[] = {
+	"left",
+	"middle",
+	"right" };
+static int buttonsCount = (int)(sizeof(buttonNames)/sizeof(*buttonNames));
+
+
+
+int keyDown(const char *code)
+	{ return heliStringmapGet(&keysPressed, code) != NULL; }
+int keyWentDown(const char *code)
+	{ return heliStringmapGet(&keysPressedInFrame, code) != NULL; }
+int keyWentUp(const char *code)
+	{ return heliStringmapGet(&keysReleasedInFrame, code) != NULL; }
+
+int mouseDidMove()
+	{ return mouseMovedInFrame; }
+int mouseDown(const char *code)
+	{ return heliStringmapGet(&buttonsPressed, code) != NULL; }
+int mouseWentDown(const char *code)
+	{ return heliStringmapGet(&buttonsPressedInFrame, code) != NULL; }
+int mouseWentUp(const char *code)
+	{ return heliStringmapGet(&buttonsReleasedInFrame, code) != NULL; }
+double mouseX()
+	{ return _mouseX; }
+double mouseY()
+	{ return _mouseY; }
+
+int mousePressedOver(Sprite sprite)
+	{ return buttonsPressed.count && mouseIsOver(sprite); }
+
+static void resize(int w, int h) {
+	width  = w > 200 ? w : 100;
+	height = h > 200 ? h : 200;
+	if (started) {
+		gtk_window_set_default_size(GTK_WINDOW(window), width, height);
+		gtk_widget_set_size_request(window, width, height);
+	}
+}
+	
+int worldGetWidth()
+	{ return width; }
+void worldSetWidth(int w)
+	{ resize(w, height); }
+
+int worldGetHeight()
+	{ return height; }
+void worldSetHeight(int h)
+	{ resize(width, h); }
+
+double worldGetFrameRate()
+	{ return frameRate; }
+void worldSetFrameRate(double frameRate) {
+	if (!(frameRate > 1)) frameRate = 1;
+	if (!(frameRate < 100)) frameRate = 100;
+}
+
+double worldGetTimeStep()
+	{ return 1/frameRate; }
+
+int worldGetFrameCount()
+	{ return (int)frameCount; }
+double worldGetSeconds()
+	{ return started ? (currentTime - startTime)*1e-6 : 0.0; }
+
+void worldSetInit(Callback init)
+	{ initCallback = init; }
+void worldSetDraw(Callback draw)
+	{ drawCallback = draw; }
+void worldStop()
+	{ if (started) stopped = TRUE; }
+
+
+void cameraOn()
+	{ cameraEnabled = TRUE; }
+void cameraOff()
+	{ cameraEnabled = FALSE; }
+int cameraIsActive()
+	{ return cameraEnabled; }
+
+double cameraMouseX()
+	{ return _mouseX/cameraZoom + cameraX; }
+double cameraMouseY()
+	{ return _mouseY/cameraZoom + cameraY; }
+
+double cameraGetX()
+	{ return cameraX; }
+void cameraSetX(double x)
+	{ cameraX = x; }
+
+double cameraGetY()
+	{ return cameraY; }
+void cameraSetY(double y)
+	{ cameraY = y; }
+
+double cameraGetZoom()
+	{ return cameraZoom; }
+void cameraSetZoom(double x)
+	{ cameraZoom = x > 1e-6 ? x : 1e-6; }
+
+static gboolean idle(gpointer data G_GNUC_UNUSED) {
+	if (stopped) {
+		if (window) {
+			gtk_window_close(GTK_WINDOW(window));
+			window = NULL;
+		}
+		return FALSE;
+	}
+	gtk_widget_queue_draw(window);
+	return TRUE;
+}
+
+static gboolean draw(GtkWidget *widget G_GNUC_UNUSED, cairo_t *cr, gpointer data G_GNUC_UNUSED) {
+	int doFrame = FALSE;
+	
+	if ( cairoSurface
+	  && cairo_image_surface_get_width(cairoSurface) != width
+	  && cairo_image_surface_get_height(cairoSurface) != height )
+		{ cairo_surface_destroy(cairoSurface); cairoSurface = NULL; }
+	if (!cairoSurface) {
+		cairoSurface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
+		doFrame = TRUE;
+	}
+
+	if (frameCount == 0) {
+		currentTime = startTime = g_get_monotonic_time();
+		doFrame = TRUE;
+	}
+
+	double dt = 1/frameRate;
+	gint64 timeStep = (gint64)round(dt*1e6);
+	gint64 newTime = g_get_monotonic_time();
+	if (currentTime < newTime)
+		doFrame = TRUE;
+	
+	if (doFrame) {
+		if (frameCount == 0) heliDoTests();
+
+		heliCairo = cairo_create(cairoSurface);
+		heliDrawingPrepareFrame();
+		if (drawCallback) drawCallback();
+		cairo_surface_flush(cairoSurface);
+		cairo_destroy(heliCairo);
+		heliCairo = NULL;
+		
+		currentTime += timeStep;
+		++frameCount;
+		heliSpriteUpdate(dt);
+		heliSoundUpdate();
+		
+		heliArrayClear(&keysPressedInFrame);
+		heliArrayClear(&keysReleasedInFrame);
+		heliArrayClear(&buttonsPressedInFrame);
+		heliArrayClear(&buttonsReleasedInFrame);
+		
+		if (stopped) g_idle_add_full(G_PRIORITY_DEFAULT, idle, NULL, NULL);
+	}
+	
+	gint64 delta = newTime - currentTime - 2000000;
+	if (delta > 0) {
+		startTime += delta;
+		currentTime += delta;
+	}
+	
+	heliDrawingClearFrame(cr);
+	cairo_save(cr);
+	cairo_set_source_surface(cr, cairoSurface, 0, 0);
+	cairo_paint(cr);
+	cairo_restore(cr);
+	
+	if (!stopped) gtk_widget_queue_draw(window);
+	
+	delta = currentTime - g_get_monotonic_time();
+	if (delta > 100) g_usleep(delta - 100);
+	
+	return TRUE;
+}
+
+static gboolean handleEvent(GtkWidget *widget G_GNUC_UNUSED, GdkEvent *event, gpointer data G_GNUC_UNUSED) {
+	gchar *keyname;
+	int button;
+	
+	switch(event->type) {
+	case GDK_KEY_PRESS:
+		keyname = heliStringCopy( gdk_keyval_name(event->key.keyval) );
+		heliLowercase(keyname);
+		heliStringmapAdd(&keysPressed, keyname, NULL, NULL);
+		heliStringmapAdd(&keysPressedInFrame, keyname, NULL, NULL);
+		free(keyname);
+		return TRUE;
+	case GDK_KEY_RELEASE:
+		keyname = heliStringCopy( gdk_keyval_name(event->key.keyval) );
+		heliLowercase(keyname);
+		heliStringmapRemove(&keysPressed, keyname);
+		heliStringmapAdd(&keysReleasedInFrame, keyname, NULL, NULL);
+		free(keyname);
+		return TRUE;
+	case GDK_BUTTON_PRESS:
+		button = event->button.button;
+		if (button >= 1 && button <= buttonsCount) {
+			heliStringmapAdd(&buttonsPressed, buttonNames[button - 1], NULL, NULL);
+			heliStringmapAdd(&buttonsPressedInFrame, buttonNames[button - 1], NULL, NULL);
+		}
+		_mouseX = event->button.x;
+		_mouseY = event->button.y;
+		return TRUE;
+	case GDK_BUTTON_RELEASE:
+		button = event->button.button;
+		if (button >= 1 && button <= buttonsCount) {
+			heliStringmapRemove(&buttonsPressed, buttonNames[button - 1]);
+			heliStringmapAdd(&buttonsReleasedInFrame, buttonNames[button - 1], NULL, NULL);
+		}
+		_mouseX = event->button.x;
+		_mouseY = event->button.y;
+		return TRUE;
+	case GDK_MOTION_NOTIFY:
+		_mouseX = event->motion.x;
+		_mouseY = event->motion.y;
+		return TRUE;
+	case GDK_DELETE:
+		stopped = TRUE;
+		window = NULL;
+		break;
+	default:
+		break;
+	}
+	return FALSE;
+}
+
+static void activate(GtkApplication* app, gpointer data G_GNUC_UNUSED) {
+	window = gtk_application_window_new(app);
+	g_signal_connect(window, "draw", G_CALLBACK(draw), NULL);
+	g_signal_connect(window, "event", G_CALLBACK(handleEvent), NULL);
+	gtk_window_set_resizable(GTK_WINDOW(window), FALSE);
+	gtk_window_set_default_size(GTK_WINDOW(window), width, height);
+	gtk_widget_add_events( window,
+						   GDK_POINTER_MOTION_MASK
+						 | GDK_BUTTON_PRESS_MASK
+						 | GDK_BUTTON_RELEASE_MASK
+						 | GDK_KEY_PRESS_MASK
+						 | GDK_KEY_RELEASE_MASK );
+	gtk_widget_set_size_request(window, width, height);
+	gtk_widget_show(window);
+
+	currentTime = startTime = 0;
+	if (initCallback) initCallback();
+	g_idle_add(idle, NULL);
+}
+
+void worldRun() {
+	if (started) return;
+	started = TRUE;
+	stopped = FALSE;
+
+	frameCount = 0;
+	srand(time(NULL));
+
+	GtkApplication *application = gtk_application_new(NULL, 0);
+	g_signal_connect(application, "activate", G_CALLBACK(activate), NULL);
+	g_application_run(G_APPLICATION(application), 0, NULL);
+	g_object_unref(application);
+	
+	heliSpriteFinish();
+	heliDrawingFinish();
+	heliAnimationFinish();
+	heliSoundFinish();
+	
+	if (cairoSurface) cairo_surface_destroy(cairoSurface);
+	cairoSurface = NULL;
+	
+	heliArrayDestroy(&keysPressed);
+	heliArrayDestroy(&keysPressed);
+	heliArrayDestroy(&keysPressedInFrame);
+	heliArrayDestroy(&keysReleasedInFrame);
+	heliArrayDestroy(&buttonsPressed);
+	heliArrayDestroy(&buttonsPressedInFrame);
+	heliArrayDestroy(&buttonsReleasedInFrame);
+	
+	started = FALSE;
+}
diff --git a/src/world.h b/src/world.h
new file mode 100644
index 0000000..c01e67f
--- /dev/null
+++ b/src/world.h
@@ -0,0 +1,74 @@
+#ifndef HELI_WORLD_H
+#define HELI_WORLD_H
+
+
+#include "common.h"
+#include "sprite.h"
+
+typedef void (*Callback)();
+typedef struct _Sound *Sound;
+
+
+void drawSprites();
+
+Sound createSound(const char *path);
+void soundDestroy(Sound sound);
+void soundPlay(Sound sound, int loop);
+void soundStop(Sound sound);
+
+int keyDown(const char *code);
+int keyWentDown(const char *code);
+int keyWentUp(const char *code);
+
+int mouseDidMove();
+int mouseDown(const char *code);
+int mouseWentDown(const char *code);
+int mouseWentUp(const char *code);
+double mouseX();
+double mouseY();
+
+int mouseIsOver(Sprite sprite);
+int mousePressedOver(Sprite sprite);
+
+
+int worldGetSpriteCount();
+Sprite worldGetSprite(int i);
+
+int worldGetWidth();
+void worldSetWidth(int width);
+
+int worldGetHeight();
+void worldSetHeight(int height);
+
+double worldGetFrameRate();
+void worldSetFrameRate(double frameRate);
+
+double worldGetTimeStep();
+
+int worldGetFrameCount();
+double worldGetSeconds();
+
+void worldSetInit(Callback init);
+void worldSetDraw(Callback draw);
+void worldRun();
+void worldStop();
+
+
+void cameraOn();
+void cameraOff();
+int cameraIsActive();
+
+double cameraMouseX();
+double cameraMouseY();
+
+double cameraGetX();
+void cameraSetX(double x);
+
+double cameraGetY();
+void cameraSetY(double y);
+
+double cameraGetZoom();
+void cameraSetZoom(double zoom);
+
+
+#endif
diff --git a/test/main.c b/test/main.c
deleted file mode 100644
index 5410171..0000000
--- a/test/main.c
+++ /dev/null
@@ -1,15 +0,0 @@
-
-#include <helianthus/helianthus.h>
-
-void init() {
-}
-
-void draw() {
-}
-
-int main() {
-	worldSetInit(&init);
-	worldSetDraw(&draw);
-	worldRun();
-	return 0;	
-}