/*- genpng

 *

 * COPYRIGHT: Written by John Cunningham Bowler, 2015.

 * To the extent possible under law, the author has waived all copyright and

 * related or neighboring rights to this work.  This work is published from:

 * United States.

 *

 * Generate a PNG with an alpha channel, correctly.

 *

 * This is a test case generator; the resultant PNG files are only of interest

 * to those of us who care about whether the edges of circles are green, red,

 * or yellow.

 *

 * The program generates an RGB+Alpha PNG of a given size containing the given

 * shapes on a transparent background:

 *

 *  genpng width height { shape }

 *    shape ::= color width shape x1 y1 x2 y2

 *

 * 'color' is:

 *

 *  black white red green yellow blue brown purple pink orange gray cyan

 *

 * The point is to have colors that are linguistically meaningful plus that old

 * bugbear of the department store dress murders, Cyan, the only color we argue

 * about.

 *

 * 'shape' is:

 *

 *  circle: an ellipse

 *  square: a rectangle

 *  line: a straight line

 *

 * Each shape is followed by four numbers, these are two points in the output

 * coordinate space (as real numbers) which describe the circle, square, or

 * line.  The shape is filled if it is preceded by 'filled' (not valid for

 * 'line') or is drawn with a line, in which case the width of the line must

 * precede the shape.

 *

 * The whole set of information can be repeated as many times as desired:

 *

 *    shape ::= color width shape x1 y1 x2 y2

 *

 *    color ::= black|white|red|green|yellow|blue

 *    color ::= brown|purple|pink|orange|gray|cyan

 *    width ::= filled

 *    width ::= <number></number>

 *    shape ::= circle|square|line

 *    x1    ::= <number></number>

 *    x2    ::= <number></number>

 *    y1    ::= <number></number>

 *    y2    ::= <number></number>

 *

 * The output PNG is generated by down-sampling a 4x supersampled image using

 * a bi-cubic filter.  The bi-cubic has a 2 (output) pixel width, so an 8x8

 * array of super-sampled points contribute to each output pixel.  The value of

 * a super-sampled point is found using an unfiltered, aliased, infinite

 * precision image: Each shape from the last to the first is checked to see if

 * the point is in the drawn area and, if it is, the color of the point is the

 * color of the shape and the alpha is 1, if not the previous shape is checked.

 *

 * This is an aliased algorithm because no filtering is done; a point is either

 * inside or outside each shape and 'close' points do not contribute to the

 * sample.  The down-sampling is relied on to correct the error of not using

 * a filter.

 *

 * The line end-caps are 'flat'; they go through the points.  The square line

 * joins are mitres; the outside of the lines are continued to the point of

 * intersection.

 */

#include <stddef.h></stddef.h>

#include <stdlib.h></stdlib.h>

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

#include <stdio.h></stdio.h>

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

/* Normally use <png.h> here to get the installed libpng, but this is done to</png.h>

 * ensure the code picks up the local libpng implementation:

 */

#include "../../png.h"

#if defined(PNG_SIMPLIFIED_WRITE_SUPPORTED) && defined(PNG_STDIO_SUPPORTED)

static const struct color

{

   const char *name;

   double      red;

   double      green;

   double      blue;

} colors[] =

/* color ::= black|white|red|green|yellow|blue

 * color ::= brown|purple|pink|orange|gray|cyan

 */

{

   { "black",   0,    0,  0 },

   { "white",   1,    1,  1 },

   { "red",     1,    0,  0 },

   { "green",   0,    1,  0 },

   { "yellow",  1,    1,  0 },

   { "blue",    0,    0,  1 },

   { "brown",  .5, .125,  0 },

   { "purple",  1,    0,  1 },

   { "pink",    1,   .5, .5 },

   { "orange",  1,   .5,  0 },

   { "gray",    0,   .5, .5 },

   { "cyan",    0,    1,  1 }

};

#define color_count ((sizeof colors)/(sizeof colors[0]))

static const struct color *

color_of(const char *arg)

{

   int icolor = color_count;

   while (--icolor >= 0)

   {

      if (strcmp(colors[icolor].name, arg) == 0)

         return colors+icolor;

   }

   fprintf(stderr, "genpng: invalid color %s\n", arg);

   exit(1);

}

static double

width_of(const char *arg)

{

   if (strcmp(arg, "filled") == 0)

      return 0;

   else

   {

      char *ep = NULL;

      double w = strtod(arg, &ep);

      if (ep != NULL && *ep == 0 && w > 0)

         return w;

   }

   fprintf(stderr, "genpng: invalid line width %s\n", arg);

   exit(1);

}

static double

coordinate_of(const char *arg)

{

   char *ep = NULL;

   double w = strtod(arg, &ep);

   if (ep != NULL && *ep == 0)

      return w;

   fprintf(stderr, "genpng: invalid coordinate value %s\n", arg);

   exit(1);

}

struct arg; /* forward declaration */

typedef int (*shape_fn_ptr)(const struct arg *arg, double x, double y);

   /* A function to determine if (x,y) is inside the shape.

    *

    * There are two implementations:

    *

    *    inside_fn: returns true if the point is inside

    *    check_fn:  returns;

    *       -1: the point is outside the shape by more than the filter width (2)

    *        0: the point may be inside the shape

    *       +1: the point is inside the shape by more than the filter width

    */

#define OUTSIDE (-1)

#define INSIDE  (1)

struct arg

{

   const struct color *color;

   shape_fn_ptr        inside_fn;

   shape_fn_ptr        check_fn;

   double              width; /* line width, 0 for 'filled' */

   double              x1, y1, x2, y2;

};

/* IMPLEMENTATION NOTE:

 *

 * We want the contribution of each shape to the sample corresponding to each

 * pixel.  This could be obtained by super sampling the image to infinite

 * dimensions, finding each point within the shape and assigning that a value

 * '1' while leaving every point outside the shape with value '0' then

 * downsampling to the image size with sinc; computationally very expensive.

 *

 * Approximations are as follows:

 *

 * 1) If the pixel coordinate is within the shape assume the sample has the

 *    shape color and is opaque, else assume there is no contribution from

 *    the shape.

 *

 *    This is the equivalent of aliased rendering or resampling an image with

 *    a block filter.  The maximum error in the calculated alpha (which will

 *    always be 0 or 1) is 0.5.

 *

 * 2) If the shape is within a square of size 1x1 centered on the pixel assume

 *    that the shape obscures an amount of the pixel equal to its area within

 *    that square.

 *

 *    This is the equivalent of 'pixel coverage' alpha calculation or resampling

 *    an image with a bi-linear filter.  The maximum error is over 0.2, but the

 *    results are often acceptable.

 *

 *    This can be approximated by applying (1) to a super-sampled image then

 *    downsampling with a bi-linear filter.  The error in the super-sampled

 *    image is 0.5 per sample, but the resampling reduces this.

 *

 * 3) Use a better filter with a super-sampled image; in the limit this is the

 *    sinc() approach.

 *

 * 4) Do the geometric calculation; a bivariate definite integral across the

 *    shape, unfortunately this means evaluating Si(x), the integral of sinc(x),

 *    which is still a lot of math.

 *

 * This code uses approach (3) with a bi-cubic filter and 8x super-sampling

 * and method (1) for the super-samples.  This means that the sample is either

 * 0 or 1, depending on whether the sub-pixel is within or outside the shape.

 * The bi-cubic weights are also fixed and the 16 required weights are

 * pre-computed here (note that the 'scale' setting will need to be changed if

 * 'super' is increased).

 *

 * The code also calculates a sum to the edge of the filter. This is not

 * currently used by could be used to optimize the calculation.

 */

#if 0 /* bc code */

scale=10

super=8

define bicubic(x) {

   if (x <= 1) return (1.5*x - 2.5)*x*x + 1;

   if (x <  2) return (((2.5 - 0.5*x)*x - 4)*x + 2);

   return 0;

}

define sum(x) {

   auto s;

   s = 0;

   while (x < 2*super) {

      s = s + bicubic(x/super);

      x = x + 1;

   }

   return s;

}

define results(x) {

   auto b, s;

   b = bicubic(x/super);

   s = sum(x);

   print "   /*", x, "*/ { ", b, ", ", s, " }";

   return 1;

}

x=0

while (x<2*super) {

   x = x + results(x)

   if (x < 2*super) print ","

   print "\n"

}

quit

#endif

#define BICUBIC1(x) /*     |x| <= 1 */ ((1.5*(x)* - 2.5)*(x)*(x) + 1)

#define BICUBIC2(x) /* 1 < |x| <  2 */ (((2.5 - 0.5*(x))*(x) - 4)*(x) + 2)

#define FILTER_WEIGHT 9 /* Twice the first sum below */

#define FILTER_WIDTH  2 /* Actually half the width; -2..+2 */

#define FILTER_STEPS  8 /* steps per filter unit */

static const double

bicubic[16][2] =

{

   /* These numbers are exact; the weight for the filter is 1/9, but this

    * would make the numbers inexact, so it is not included here.

    */

   /*          bicubic      sum        */

   /* 0*/ { 1.0000000000, 4.5000000000 },

   /* 1*/ {  .9638671875, 3.5000000000 },

   /* 2*/ {  .8671875000, 2.5361328125 },

   /* 3*/ {  .7275390625, 1.6689453125 },

   /* 4*/ {  .5625000000,  .9414062500 },

   /* 5*/ {  .3896484375,  .3789062500 },

   /* 6*/ {  .2265625000, -.0107421875 },

   /* 7*/ {  .0908203125, -.2373046875 },

   /* 8*/ {            0, -.3281250000 },

   /* 9*/ { -.0478515625, -.3281250000 },

   /*10*/ { -.0703125000, -.2802734375 },

   /*11*/ { -.0732421875, -.2099609375 },

   /*12*/ { -.0625000000, -.1367187500 },

   /*13*/ { -.0439453125, -.0742187500 },

   /*14*/ { -.0234375000, -.0302734375 },

   /*15*/ { -.0068359375, -.0068359375 }

};

static double

alpha_calc(const struct arg *arg, double x, double y)

{

   /* For [x-2..x+2],[y-2,y+2] calculate the weighted bicubic given a function

    * which tells us whether a point is inside or outside the shape.  First

    * check if we need to do this at all:

    */

   switch (arg->check_fn(arg, x, y))

   {

      case OUTSIDE:

         return 0; /* all samples outside the shape */

      case INSIDE:

         return 1; /* all samples inside the shape */

      default:

      {

         int dy;

         double alpha = 0;

#        define FILTER_D (FILTER_WIDTH*FILTER_STEPS-1)

         for (dy=-FILTER_D; dy<=FILTER_D; ++dy)

         {

            double wy = bicubic[abs(dy)][0];

            if (wy != 0)

            {

               double alphay = 0;

               int dx;

               for (dx=-FILTER_D; dx<=FILTER_D; ++dx)

               {

                  double wx = bicubic[abs(dx)][0];

                  if (wx != 0 && arg->inside_fn(arg, x+dx/16, y+dy/16))

                     alphay += wx;

               }

               alpha += wy * alphay;

            }

         }

         /* This needs to be weighted for each dimension: */

         return alpha / (FILTER_WEIGHT*FILTER_WEIGHT);

      }

   }

}

/* These are the shape functions. */

/* "square",

 * { inside_square_filled, check_square_filled },

 * { inside_square, check_square }

 */

static int

square_check(double x, double y, double x1, double y1, double x2, double y2)

   /* Is x,y inside the square (x1,y1)..(x2,y2)? */

{

   /* Do a modified Cohen-Sutherland on one point, bit patterns that indicate

    * 'outside' are:

    *

    *   x

    *    0      x      0      x     To the right

    *    1      x      1      x     To the left

    *    x      0      x      0     Below

    *    x      1      x      1     Above

    *

    * So 'inside' is (x

    */

   return ((x

}

static int

inside_square_filled(const struct arg *arg, double x, double y)

{

   return square_check(x, y, arg->x1, arg->y1, arg->x2, arg->y2);

}

static int

square_check_line(const struct arg *arg, double x, double y, double w)

   /* Check for a point being inside the boundaries implied by the given arg

    * and assuming a width 2*w each side of the boundaries.  This returns the

    * 'check' INSIDE/OUTSIDE/0 result but note the semantics:

    *

    *          +--------------+

    *          |              |   OUTSIDE

    *          |   INSIDE     |

    *          |              |

    *          +--------------+

    *

    * And '0' means within the line boundaries.

    */

{

   double cx = (arg->x1+arg->x2)/2;

   double wx = fabs(arg->x1-arg->x2)/2;

   double cy = (arg->y1+arg->y2)/2;

   double wy = fabs(arg->y1-arg->y2)/2;

   if (square_check(x, y, cx-wx-w, cy-wy-w, cx+wx+w, cy+wy+w))

   {

      /* Inside, but maybe too far; check for the redundant case where

       * the lines overlap:

       */

      wx -= w;

      wy -= w;

      if (wx > 0 && wy > 0 && square_check(x, y, cx-wx, cy-wy, cx+wx, cy+wy))

         return INSIDE; /* between (inside) the boundary lines. */

      return 0; /* inside the lines themselves. */

   }

   return OUTSIDE; /* outside the boundary lines. */

}

static int

check_square_filled(const struct arg *arg, double x, double y)

{

   /* The filter extends +/-FILTER_WIDTH each side of each output point, so

    * the check has to expand and contract the square by that amount; '0'

    * means close enough to the edge of the square that the bicubic filter has

    * to be run, OUTSIDE means alpha==0, INSIDE means alpha==1.

    */

   return square_check_line(arg, x, y, FILTER_WIDTH);

}

static int

inside_square(const struct arg *arg, double x, double y)

{

   /* Return true if within the drawn lines, else false, no need to distinguish

    * INSIDE vs OUTSIDE here:

    */

   return square_check_line(arg, x, y, arg->width/2) == 0;

}

static int

check_square(const struct arg *arg, double x, double y)

{

   /* So for this function a result of 'INSIDE' means inside the actual lines.

    */

   double w = arg->width/2;

   if (square_check_line(arg, x, y, w+FILTER_WIDTH) == 0)

   {

      /* Somewhere close to the boundary lines. If far enough inside one of

       * them then we can return INSIDE:

       */

      w -= FILTER_WIDTH;

      if (w > 0 && square_check_line(arg, x, y, w) == 0)

         return INSIDE;

      /* Point is somewhere in the filter region: */

      return 0;

   }

   else /* Inside or outside the square by more than w+FILTER_WIDTH. */

      return OUTSIDE;

}

/* "circle",

 * { inside_circle_filled, check_circle_filled },

 * { inside_circle, check_circle }

 *

 * The functions here are analoguous to the square ones; however, they check

 * the corresponding ellipse as opposed to the rectangle.

 */

static int

circle_check(double x, double y, double x1, double y1, double x2, double y2)

{

   if (square_check(x, y, x1, y1, x2, y2))

   {

      /* Inside the square, so maybe inside the circle too: */

      const double cx = (x1 + x2)/2;

      const double cy = (y1 + y2)/2;

      const double dx = x1 - x2;

      const double dy = y1 - y2;

      x = (x - cx)/dx;

      y = (y - cy)/dy;

      /* It is outside if the distance from the center is more than half the

       * diameter:

       */

      return x*x+y*y < .25;

   }

   return 0; /* outside */

}

static int

inside_circle_filled(const struct arg *arg, double x, double y)

{

   return circle_check(x, y, arg->x1, arg->y1, arg->x2, arg->y2);

}

static int

circle_check_line(const struct arg *arg, double x, double y, double w)

   /* Check for a point being inside the boundaries implied by the given arg

    * and assuming a width 2*w each side of the boundaries.  This function has

    * the same semantic as square_check_line but tests the circle.

    */

{

   double cx = (arg->x1+arg->x2)/2;

   double wx = fabs(arg->x1-arg->x2)/2;

   double cy = (arg->y1+arg->y2)/2;

   double wy = fabs(arg->y1-arg->y2)/2;

   if (circle_check(x, y, cx-wx-w, cy-wy-w, cx+wx+w, cy+wy+w))

   {

      /* Inside, but maybe too far; check for the redundant case where

       * the lines overlap:

       */

      wx -= w;

      wy -= w;

      if (wx > 0 && wy > 0 && circle_check(x, y, cx-wx, cy-wy, cx+wx, cy+wy))

         return INSIDE; /* between (inside) the boundary lines. */

      return 0; /* inside the lines themselves. */

   }

   return OUTSIDE; /* outside the boundary lines. */

}

static int

check_circle_filled(const struct arg *arg, double x, double y)

{

   return circle_check_line(arg, x, y, FILTER_WIDTH);

}

static int

inside_circle(const struct arg *arg, double x, double y)

{

   return circle_check_line(arg, x, y, arg->width/2) == 0;

}

static int

check_circle(const struct arg *arg, double x, double y)

{

   /* Exactly as the 'square' code.  */

   double w = arg->width/2;

   if (circle_check_line(arg, x, y, w+FILTER_WIDTH) == 0)

   {

      w -= FILTER_WIDTH;

      if (w > 0 && circle_check_line(arg, x, y, w) == 0)

         return INSIDE;

      /* Point is somewhere in the filter region: */

      return 0;

   }

   else /* Inside or outside the square by more than w+FILTER_WIDTH. */

      return OUTSIDE;

}

/* "line",

 * { NULL, NULL },  There is no 'filled' line.

 * { inside_line, check_line }

 */

static int

line_check(double x, double y, double x1, double y1, double x2, double y2,

   double w, double expand)

{

   /* Shift all the points to (arg->x1, arg->y1) */

   double lx = x2 - x1;

   double ly = y2 - y1;

   double len2 = lx*lx + ly*ly;

   double cross, dot;

   x -= x1;

   y -= y1;

   /* The dot product is the distance down the line, the cross product is

    * the distance away from the line:

    *

    *    distance = |cross| / sqrt(len2)

    */

   cross = x * ly - y * lx;

   /* If 'distance' is more than w the point is definitely outside the line:

    *

    *     distance >= w

    *     |cross|  >= w * sqrt(len2)

    *     cross^2  >= w^2 * len2:

    */

   if (cross*cross >= (w+expand)*(w+expand)*len2)

      return 0; /* outside */

   /* Now find the distance *along* the line; this comes from the dot product

    * lx.x+ly.y. The actual distance (in pixels) is:

    *

    *   distance = dot / sqrt(len2)

    */

   dot = lx * x + ly * y;

   /* The test for 'outside' is:

    *

    *    distance < 0 || distance > sqrt(len2)

    *                 -> dot / sqrt(len2) > sqrt(len2)

    *                 -> dot > len2

    *

    * But 'expand' is used for the filter width and needs to be handled too:

    */

   return dot > -expand && dot < len2+expand;

}

static int

inside_line(const struct arg *arg, double x, double y)

{

   return line_check(x, y, arg->x1, arg->y1, arg->x2, arg->y2, arg->width/2, 0);

}

static int

check_line(const struct arg *arg, double x, double y)

{

   /* The end caps of the line must be checked too; it's not enough just to

    * widen the line by FILTER_WIDTH; 'expand' exists for this purpose:

    */

   if (line_check(x, y, arg->x1, arg->y1, arg->x2, arg->y2, arg->width/2,

       FILTER_WIDTH))

   {

      /* Inside the line+filter; far enough inside that the filter isn't

       * required?

       */

      if (arg->width > 2*FILTER_WIDTH &&

          line_check(x, y, arg->x1, arg->y1, arg->x2, arg->y2, arg->width/2,

             -FILTER_WIDTH))

         return INSIDE;

      return 0;

   }

   return OUTSIDE;

}

static const struct

{

   const char    *name;

   shape_fn_ptr   function[2/*fill,line*/][2];

#  define         FN_INSIDE 0

#  define         FN_CHECK 1

} shape_defs[] =

{

   {  "square",

      {  { inside_square_filled, check_square_filled },

         { inside_square, check_square } }

   },

   {  "circle",

      {  { inside_circle_filled, check_circle_filled },

         { inside_circle, check_circle } }

   },

   {  "line",

      {  { NULL, NULL },

         { inside_line, check_line } }

   }

};

#define shape_count ((sizeof shape_defs)/(sizeof shape_defs[0]))

static shape_fn_ptr

shape_of(const char *arg, double width, int f)

{

   unsigned int i;

   for (i=0; i

   {

      shape_fn_ptr fn = shape_defs[i].function[width != 0][f];

      if (fn != NULL)

         return fn;

      fprintf(stderr, "genpng: %s %s not supported\n",

         width == 0 ? "filled" : "unfilled", arg);

      exit(1);

   }

   fprintf(stderr, "genpng: %s: not a valid shape name\n", arg);

   exit(1);

}

static void

parse_arg(struct arg *arg, const char **argv/*7 arguments*/)

{

   /* shape ::= color width shape x1 y1 x2 y2 */

   arg->color = color_of(argv[0]);

   arg->width = width_of(argv[1]);

   arg->inside_fn = shape_of(argv[2], arg->width, FN_INSIDE);

   arg->check_fn = shape_of(argv[2], arg->width, FN_CHECK);

   arg->x1 = coordinate_of(argv[3]);

   arg->y1 = coordinate_of(argv[4]);

   arg->x2 = coordinate_of(argv[5]);

   arg->y2 = coordinate_of(argv[6]);

}

static png_uint_32

read_wh(const char *name, const char *str)

   /* read a PNG width or height */

{

   char *ep = NULL;

   unsigned long ul = strtoul(str, &ep, 10);

   if (ep != NULL && *ep == 0 && ul > 0 && ul <= 0x7fffffff)

      return (png_uint_32)/*SAFE*/ul;

   fprintf(stderr, "genpng: %s: invalid number %s\n", name, str);

   exit(1);

}

static void

pixel(png_uint_16p p, struct arg *args, int nargs, double x, double y)

{

   /* Fill in the pixel by checking each shape (args[nargs]) for effects on

    * the corresponding sample:

    */

   double r=0, g=0, b=0, a=0;

   while (--nargs >= 0 && a != 1)

   {

      /* NOTE: alpha_calc can return a value outside the range 0..1 with the

       * bicubic filter.

       */

      const double alpha = alpha_calc(args+nargs, x, y) * (1-a);

      r += alpha * args[nargs].color->red;

      g += alpha * args[nargs].color->green;

      b += alpha * args[nargs].color->blue;

      a += alpha;

   }

   /* 'a' may be negative or greater than 1; if it is, negative clamp the

    * pixel to 0 if >1 clamp r/g/b:

    */

   if (a > 0)

   {

      if (a > 1)

      {

         if (r > 1) r = 1;

         if (g > 1) g = 1;

         if (b > 1) b = 1;

         a = 1;

      }

      /* And fill in the pixel: */

      p[0] = (png_uint_16)/*SAFE*/round(r * 65535);

      p[1] = (png_uint_16)/*SAFE*/round(g * 65535);

      p[2] = (png_uint_16)/*SAFE*/round(b * 65535);

      p[3] = (png_uint_16)/*SAFE*/round(a * 65535);

   }

   else

      p[3] = p[2] = p[1] = p[0] = 0;

}

int

main(int argc, const char **argv)

{

   int convert_to_8bit = 0;

   /* There is one option: --8bit: */

   if (argc > 1 && strcmp(argv[1], "--8bit") == 0)

      --argc, ++argv, convert_to_8bit = 1;

   if (argc >= 3)

   {

      png_uint_16p buffer;

      int nshapes;

      png_image image;

#     define max_shapes 256

      struct arg arg_list[max_shapes];

      /* The libpng Simplified API write code requires a fully initialized

       * structure.

       */

      memset(&image, 0, sizeof image);

      image.version = PNG_IMAGE_VERSION;

      image.opaque = NULL;

      image.width = read_wh("width", argv[1]);

      image.height = read_wh("height", argv[2]);

      image.format = PNG_FORMAT_LINEAR_RGB_ALPHA;

      image.flags = 0;

      image.colormap_entries = 0;

      /* Check the remainder of the arguments */

      for (nshapes=0; 3+7*(nshapes+1) <= argc && nshapes < max_shapes;

           ++nshapes)

         parse_arg(arg_list+nshapes, argv+3+7*nshapes);

      if (3+7*nshapes != argc)

      {

         fprintf(stderr, "genpng: %s: too many arguments\n", argv[3+7*nshapes]);

         return 1;

      }

      /* Create the buffer: */

      buffer = malloc(PNG_IMAGE_SIZE(image));

      if (buffer != NULL)

      {

         png_uint_32 y;

         /* Write each row... */

         for (y=0; y

         {

            png_uint_32 x;

            /* Each pixel in each row: */

            for (x=0; x

               pixel(buffer + 4*(x + y*image.width), arg_list, nshapes, x, y);

         }

         /* Write the result (to stdout) */

         if (png_image_write_to_stdio(&image, stdout, convert_to_8bit,

             buffer, 0/*row_stride*/, NULL/*colormap*/))

         {

            free(buffer);

            return 0; /* success */

         }

         else

            fprintf(stderr, "genpng: write stdout: %s\n", image.message);

         free(buffer);

      }

      else

         fprintf(stderr, "genpng: out of memory: %lu bytes\n",

               (unsigned long)PNG_IMAGE_SIZE(image));

   }

   else

   {

      /* Wrong number of arguments */

      fprintf(stderr, "genpng: usage: genpng [--8bit] width height {shape}\n"

         " Generate a transparent PNG in RGBA (truecolor+alpha) format\n"

         " containing the given shape or shapes.  Shapes are defined:\n"

         "\n"

         "  shape ::= color width shape x1 y1 x2 y2\n"

         "  color ::= black|white|red|green|yellow|blue\n"

         "  color ::= brown|purple|pink|orange|gray|cyan\n"

         "  width ::= filled|<number>\n"</number>

         "  shape ::= circle|square|line\n"

         "  x1,x2 ::= <number>\n"</number>

         "  y1,y2 ::= <number>\n"</number>

         "\n"

         " Numbers are floating point numbers describing points relative to\n"

         " the top left of the output PNG as pixel coordinates.  The 'width'\n"

         " parameter is either the width of the line (in output pixels) used\n"

         " to draw the shape or 'filled' to indicate that the shape should\n"

         " be filled with the color.\n"

         "\n"

         " Colors are interpreted loosely to give access to the eight full\n"

         " intensity RGB values:\n"

         "\n"

         "  black, red, green, blue, yellow, cyan, purple, white,\n"

         "\n"

         " Cyan is full intensity blue+green; RGB(0,1,1), plus the following\n"

         " lower intensity values:\n"

         "\n"

         "  brown:  red+orange:  RGB(0.5, 0.125, 0) (dark red+orange)\n"

         "  pink:   red+white:   RGB(1.0, 0.5,   0.5)\n"

         "  orange: red+yellow:  RGB(1.0, 0.5,   0)\n"

         "  gray:   black+white: RGB(0.5, 0.5,   0.5)\n"

         "\n"

         " The RGB values are selected to make detection of aliasing errors\n"

         " easy. The names are selected to make the description of errors\n"

         " easy.\n"

         "\n"

         " The PNG is written to stdout, if --8bit is given a 32bpp RGBA sRGB\n"

         " file is produced, otherwise a 64bpp RGBA linear encoded file is\n"

         " written.\n");

   }

   return 1;

}

#endif /* SIMPLIFIED_WRITE && STDIO */