Writing libpng template

template_ping.c

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

int width, height;
int main(){
   width = 1500; height = 1000;
   char filename[] = "t.png";
  
   /*open stream */
   FILE *fp = fopen(filename, "wb");
   if (fp==NULL){
      perror(filename);
      exit(1);
   }

   png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
   if (!png) {fprintf(stderr, "png_structp_png at line %d: failed\n", __LINE__); return 1;}

   png_infop info = png_create_info_struct(png);
   if (!info) {fprintf(stderr, "png_infop at line %d: failed\n", __LINE__); return 1;}

   if (setjmp(png_jmpbuf(png))) {fprintf(stderr, "setjump at line %d: abort\n", __LINE__); return 1;}

   png_init_io(png, fp);

   png_set_IHDR(
      png,
      info,
      width, height,
      8,
      PNG_COLOR_TYPE_RGBA,
      PNG_INTERLACE_NONE,
      PNG_COMPRESSION_TYPE_DEFAULT,
      PNG_FILTER_TYPE_DEFAULT);
   png_write_info(png, info);

   png_bytep *row = NULL;
   row = (png_bytep*) malloc(sizeof(png_bytep)*height);
   if (row == NULL) {fprintf(stderr, "malloc at line %d: failed\n", __LINE__); return 1;}
   for (int y = 0; y < height; y++) {
      row[y] = malloc(sizeof(png_bytep)*width);
      if (row[y] == NULL) {fprintf(stderr, "allocating row failed: memory leak occured!! \n");return 1;}

      png_bytep line = row[y];
      png_byte val0 = 0x00;
      for (int x = 0; x < width; x++){
         png_bytep px = (line+(x*4));
         px[0] =val0;val0++;val0%=0xFF;
         px[1] = px[0];
         px[2] = px[0]
         px[3] = 0xFF;
      }
   }
   png_write_image(png, row);
   png_write_end(png, NULL);

   for (int y = 0; y < height; y++) free(row[y]);
   free(row);

   fclose(fp);
   png_destroy_write_struct(&png, &info);

   return 0;
}