/* Generate PNG of a particular size and color.

   ./make_png width height > white.png
   ./make_png width height r g b > opaque.png
   ./make_png width height r g b a > full_color.png
*/

#include<png.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>

#ifdef _WIN32
   #include<fcntl.h>
   #include<io.h>
#endif

int main(int argc, char **argv)
{
   int width = -1, height = -1, r = 255, g = 255, b = 255, a = 255, i;
   png_image image;
   png_bytep pixels;

   /* Parse and validate command line settings. */
   if( argc >= 3 )
   {
      width = atoi(argv[1]);
      height = atoi(argv[2]);
      if( argc >= 6 )
      {
         r = atoi(argv[3]);
         g = atoi(argv[4]);
         b = atoi(argv[5]);
         if( argc >= 7 )
         {
            a = atoi(argv[6]);
            if( argc > 7 )
               width = -1;  /* Too many arguments. */
         }
      }
   }
   if( width <= 0 || height <= 0 ||
       r < 0 || r > 255 || g < 0 || g > 255 || b < 0 || b > 255 ||
       a < 0 || a > 255 )
   {
      printf("%s <width> <height> [<r> <g> <b> [<a>]] > output.png\n", *argv);
      return 1;
   }

   if( isatty(STDOUT_FILENO) )
   {
      fputs("Output should be redirected to a PNG file.\n", stderr);
      return 1;
   }
   #ifdef _WIN32
      setmode(STDOUT_FILENO, O_BINARY);
   #endif

   /* Generate output. */
   memset(&image, 0, sizeof(image));
   image.version = PNG_IMAGE_VERSION;
   image.format = PNG_FORMAT_RGBA;
   image.width = width;
   image.height = height;
   pixels = (png_bytep)malloc(width * height * 4);
   if( pixels == NULL )
   {
      fputs("Out of memory.\n", stderr);
      return 1;
   }
   for(i = 0; i < width * height; i++)
   {
      pixels[i * 4] = r;
      pixels[i * 4 + 1] = g;
      pixels[i * 4 + 2] = b;
      pixels[i * 4 + 3] = a;
   }

   /* Write output. */
   if( !png_image_write_to_stdio(&image, stdout, 0, pixels, 0, NULL) )
   {
      fputs("Error writing output.\n", stderr);
      return 1;
   }

   free(pixels);
   return 0;
}