Function stbi__create_png_alpha_expand8

include/stb/stb_image.h:4675–4693

adds an extra all-255 alpha channel dest == src is legal img_n must be 1 or 3

// dest == src is legal
// img_n must be 1 or 3
static void stbi__create_png_alpha_expand8(stbi_uc *dest, stbi_uc *src, stbi__uint32 x, int img_n)
{
   int i;
   // must process data backwards since we allow dest==src
   if (img_n == 1) {
      for (i=x-1; i >= 0; --i) {
         dest[i*2+1] = 255;
         dest[i*2+0] = src[i];
      }
   } else {
      STBI_ASSERT(img_n == 3);
      for (i=x-1; i >= 0; --i) {
         dest[i*4+3] = 255;
         dest[i*4+2] = src[i*3+2];
         dest[i*4+1] = src[i*3+1];
         dest[i*4+0] = src[i*3+0];
      }
   }
}

// create the png data from post-deflated data
static int stbi__create_png_image_raw(stbi__png *a, stbi_uc *raw, stbi__uint32 raw_len, int out_n, stbi__uint32 x, stbi__uint32 y, int depth, int color)