lb.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <assert.h>
#include <png.h>

#ifdef NDEBUG
#error "Don't turn NDEBUG!!"
#endif

static png_byte
x2val (int x)
{
  double p = pow (M_E, (double) x / 150.0);
  return (p > 255.0) ? (png_byte) 255 : (png_byte) p;
}

int
main ()
{
#pragma omp parallel for
  for (int file = 0; file < 300; file++)
    {
      FILE *fpout = NULL;
      png_bytep *rowp = malloc (sizeof (png_bytep) * 700);
      assert (rowp != NULL);
#pragma omp parallel for
      for (int y = 0; y < 700; y++)
        assert ((rowp[y] = malloc (4 * 1000)) != NULL);


      char buff[50] = { 0 };
      sprintf (buff, "tt-%03d.png", file);
      fpout = fopen (buff, "wb");
      if (fpout == NULL)
        {
          perror (buff);
          exit (1);;

        }
      png_structp png =
        png_create_write_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
      assert (png != NULL);

      png_infop info = png_create_info_struct (png);
      assert (info != NULL);

      if (setjmp (png_jmpbuf (png)))
        abort ();
      png_init_io (png, fpout);

// INDENT-OFF
      png_set_IHDR (png,
                    info,
                    1000, 700,
                    8,
                    PNG_COLOR_TYPE_RGBA,
                    PNG_INTERLACE_NONE,
                    PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
// INDENT-ON
      png_write_info (png, info);
      printf ("%s\n", buff);

      for (int y = 0; y < 700; y++)
        {
          png_bytep row = rowp[y];
          for (int x = 0; x < 1000; x++)
            {
              memset (row + (x * 4), x2val (x + (file * 4)), 4);
              row[(x * 4) + 3] = 255;
            }

        }
      png_write_image (png, rowp);
      png_write_end (png, NULL);
      fclose (fpout);
      png_destroy_write_struct (&png, &info);
#pragma omp parallel for
      for (int y = 0; y < 700; y++)
          free (rowp[y]);
      free (rowp);


    }

  return 0;

}