static void stbiw__encode_png_line()

in Support/STBImage/include/stb_image_write.h [1038:1072]

• 32 lines of code
• 24 McCabe index (conditional complexity)

static void stbiw__encode_png_line(unsigned char *pixels, int stride_bytes, int width, int height, int y, int n, int filter_type, signed char *line_buffer)
{
   static int mapping[] = { 0,1,2,3,4 };
   static int firstmap[] = { 0,1,0,5,6 };
   int *mymap = (y != 0) ? mapping : firstmap;
   int i;
   int type = mymap[filter_type];
   unsigned char *z = pixels + stride_bytes * (stbi__flip_vertically_on_write ? height-1-y : y);
   int signed_stride = stbi__flip_vertically_on_write ? -stride_bytes : stride_bytes;

   if (type==0) {
      memcpy(line_buffer, z, width*n);
      return;
   }

   // first loop isn't optimized since it's just one pixel
   for (i = 0; i < n; ++i) {
      switch (type) {
         case 1: line_buffer[i] = z[i]; break;
         case 2: line_buffer[i] = z[i] - z[i-signed_stride]; break;
         case 3: line_buffer[i] = z[i] - (z[i-signed_stride]>>1); break;
         case 4: line_buffer[i] = (signed char) (z[i] - stbiw__paeth(0,z[i-signed_stride],0)); break;
         case 5: line_buffer[i] = z[i]; break;
         case 6: line_buffer[i] = z[i]; break;
      }
   }
   switch (type) {
      case 1: for (i=n; i < width*n; ++i) line_buffer[i] = z[i] - z[i-n]; break;
      case 2: for (i=n; i < width*n; ++i) line_buffer[i] = z[i] - z[i-signed_stride]; break;
      case 3: for (i=n; i < width*n; ++i) line_buffer[i] = z[i] - ((z[i-n] + z[i-signed_stride])>>1); break;
      case 4: for (i=n; i < width*n; ++i) line_buffer[i] = z[i] - stbiw__paeth(z[i-n], z[i-signed_stride], z[i-signed_stride-n]); break;
      case 5: for (i=n; i < width*n; ++i) line_buffer[i] = z[i] - (z[i-n]>>1); break;
      case 6: for (i=n; i < width*n; ++i) line_buffer[i] = z[i] - stbiw__paeth(z[i-n], 0,0); break;
   }
}