#include <math.h></math.h>

#include <string.h></string.h>

#include <helianthus.h></helianthus.h>

#define MAXCOUNT 10000

#define SPEED    1

#define SPS      500

#define PERSP    0.5

typedef struct Star {

  double x, y, z;

  double px, py;

  int visible;

} Star;

Star stars[MAXCOUNT];

double step;

double mx, my;

Framebuffer buffer;

Animation anim;

void update(double dt) {

  double dz = SPEED*dt;

  double sx =  mx*dz*PERSP;

  double sy = -my*dz*PERSP;

  int j = 0, count = 0;

  for(int i = 0; i < MAXCOUNT; ++i) {

    if (stars[i].visible) {

      double x = stars[i].x - sx*stars[i].z;

      double y = stars[i].y - sy*stars[i].z;

      double z = stars[i].z + sx*stars[i].x + sy*stars[i].y;

      stars[i].x = x;

      stars[i].y = y;

      stars[i].z = z - dz;

    } else {

      j = i;

      ++count;

    }

  }

  step += SPS*dt;

  if (count > (int)step) count = (int)step;

  step -= (int)step;

  for(int i = 0; i < count; ++i) {

    while(stars[j].visible) j = (j+1)%MAXCOUNT;

    stars[j].px = 2*randomFloat() - 1;

    stars[j].py = 2*randomFloat() - 1;

    stars[j].z = 1 - randomFloat()*dz;

    stars[j].x = stars[j].px * stars[j].z / PERSP;

    stars[j].y = stars[j].py * stars[j].z / PERSP;

    stars[j].visible = TRUE;

  }

}

void init() {

  background(COLOR_BLACK);

  buffer = createFramebuffer(windowGetWidth(), windowGetHeight());

  anim = createAnimationFromFramebuffer(buffer);

}

void draw() {

  double w = windowGetWidth();

  double h = windowGetHeight();

  double s = 0.5*(w > h ? w : h);

  saveState();

  noStroke();

  target(buffer);

  update(windowGetFrameTime());

  fill(colorByRGBA(0, 0, 0, 0.25));

  rect(0, 0, w, h);

  saveState();

  translate(w/2, h/2);

  zoom(s);

  mx = mouseTransformedX();

  my = mouseTransformedY();

  stroke(COLOR_WHITE);

  double dz = 0.01;

  for(int i = 0; i < MAXCOUNT; ++i) {

    if (stars[i].visible) {

      double z = stars[i].z > dz ? stars[i].z : dz;

      double x = stars[i].x/z*PERSP;

      double y = stars[i].y/z*PERSP;

      double r = 0.25/s/z;

      strokeWidth(r);

      line(stars[i].px, stars[i].py, x, y);

      stars[i].px = x;

      stars[i].py = y;

      stars[i].visible = stars[i].z > dz && fabs(x)-r < 1 && fabs(y)-r < 1;

    }

  }

  restoreState();

  noTarget(buffer);

  fill(COLOR_WHITE);

  rectTextured(anim, 0, 0, w, h);

  restoreState();

}

int main() {

  windowSetSize(1024, 768);

  windowSetVariableFrameRate();

  windowSetInit(&init);

  windowSetDraw(&draw);

  windowRun();

}