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)
{
   int bytes = (depth == 16? 2 : 1);
   stbi__context *s = a->s;
   stbi__uint32 i,j,stride = x*out_n*bytes;
   stbi__uint32 img_len, img_width_bytes;
   int k;
   int img_n = s->img_n; // copy it into a local for later

   int output_bytes = out_n*bytes;
   int filter_bytes = img_n*bytes;
   int width = x;

   STBI_ASSERT(out_n == s->img_n || out_n == s->img_n+1);
   a->out = (stbi_uc *) stbi__malloc_mad3(x, y, output_bytes, 0); // extra bytes to write off the end into
   if (!a->out) return stbi__err("outofmem", "Out of memory");

   if (!stbi__mad3sizes_valid(img_n, x, depth, 7)) return stbi__err("too large", "Corrupt PNG");
   img_width_bytes = (((img_n * x * depth) + 7) >> 3);
   img_len = (img_width_bytes + 1) * y;

   // we used to check for exact match between raw_len and img_len on non-interlaced PNGs,
   // but issue #276 reported a PNG in the wild that had extra data at the end (all zeros),
   // so just check for raw_len < img_len always.
   if (raw_len < img_len) return stbi__err("not enough pixels","Corrupt PNG");

   for (j=0; j < y; ++j) {
      stbi_uc *cur = a->out + stride*j;
      stbi_uc *prior;
      int filter = *raw++;

      if (filter > 4)
         return stbi__err("invalid filter","Corrupt PNG");

      if (depth < 8) {
         if (img_width_bytes > x) return stbi__err("invalid width","Corrupt PNG");
         cur += x*out_n - img_width_bytes; // store output to the rightmost img_len bytes, so we can decode in place
         filter_bytes = 1;
         width = img_width_bytes;
      }
      prior = cur - stride; // bugfix: need to compute this after 'cur +=' computation above

      // if first row, use special filter that doesn't sample previous row
      if (j == 0) filter = first_row_filter[filter];

      // handle first byte explicitly
      for (k=0; k < filter_bytes; ++k) {
         switch (filter) {
            case STBI__F_none       : cur[k] = raw[k]; break;
            case STBI__F_sub        : cur[k] = raw[k]; break;
            case STBI__F_up         : cur[k] = STBI__BYTECAST(raw[k] + prior[k]); break;
            case STBI__F_avg        : cur[k] = STBI__BYTECAST(raw[k] + (prior[k]>>1)); break;
            case STBI__F_paeth      : cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(0,prior[k],0)); break;
            case STBI__F_avg_first  : cur[k] = raw[k]; break;
            case STBI__F_paeth_first: cur[k] = raw[k]; break;
         }
      }

      if (depth == 8) {
         if (img_n != out_n)
            cur[img_n] = 255; // first pixel
         raw += img_n;
         cur += out_n;
         prior += out_n;
      } else if (depth == 16) {
         if (img_n != out_n) {
            cur[filter_bytes]   = 255; // first pixel top byte
            cur[filter_bytes+1] = 255; // first pixel bottom byte
         }
         raw += filter_bytes;
         cur += output_bytes;
         prior += output_bytes;
      } else {
         raw += 1;
         cur += 1;
         prior += 1;
      }

      // this is a little gross, so that we don't switch per-pixel or per-component
      if (depth < 8 || img_n == out_n) {
         int nk = (width - 1)*filter_bytes;
         #define STBI__CASE(f) \
             case f:     \
                for (k=0; k < nk; ++k)
         switch (filter) {
            // "none" filter turns into a memcpy here; make that explicit.
            case STBI__F_none:         memcpy(cur, raw, nk); break;
            STBI__CASE(STBI__F_sub)          { cur[k] = STBI__BYTECAST(raw[k] + cur[k-filter_bytes]); } break;
            STBI__CASE(STBI__F_up)           { cur[k] = STBI__BYTECAST(raw[k] + prior[k]); } break;
            STBI__CASE(STBI__F_avg)          { cur[k] = STBI__BYTECAST(raw[k] + ((prior[k] + cur[k-filter_bytes])>>1)); } break;
            STBI__CASE(STBI__F_paeth)        { cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(cur[k-filter_bytes],prior[k],prior[k-filter_bytes])); } break;
            STBI__CASE(STBI__F_avg_first)    { cur[k] = STBI__BYTECAST(raw[k] + (cur[k-filter_bytes] >> 1)); } break;
            STBI__CASE(STBI__F_paeth_first)  { cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(cur[k-filter_bytes],0,0)); } break;
         }
         #undef STBI__CASE
         raw += nk;
      } else {
         STBI_ASSERT(img_n+1 == out_n);
         #define STBI__CASE(f) \
             case f:     \
                for (i=x-1; i >= 1; --i, cur[filter_bytes]=255,raw+=filter_bytes,cur+=output_bytes,prior+=output_bytes) \
                   for (k=0; k < filter_bytes; ++k)
         switch (filter) {
            STBI__CASE(STBI__F_none)         { cur[k] = raw[k]; } break;
            STBI__CASE(STBI__F_sub)          { cur[k] = STBI__BYTECAST(raw[k] + cur[k- output_bytes]); } break;
            STBI__CASE(STBI__F_up)           { cur[k] = STBI__BYTECAST(raw[k] + prior[k]); } break;
            STBI__CASE(STBI__F_avg)          { cur[k] = STBI__BYTECAST(raw[k] + ((prior[k] + cur[k- output_bytes])>>1)); } break;
            STBI__CASE(STBI__F_paeth)        { cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(cur[k- output_bytes],prior[k],prior[k- output_bytes])); } break;
            STBI__CASE(STBI__F_avg_first)    { cur[k] = STBI__BYTECAST(raw[k] + (cur[k- output_bytes] >> 1)); } break;
            STBI__CASE(STBI__F_paeth_first)  { cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(cur[k- output_bytes],0,0)); } break;
         }
         #undef STBI__CASE

         // the loop above sets the high byte of the pixels' alpha, but for
         // 16 bit png files we also need the low byte set. we'll do that here.
         if (depth == 16) {
            cur = a->out + stride*j; // start at the beginning of the row again
            for (i=0; i < x; ++i,cur+=output_bytes) {
               cur[filter_bytes+1] = 255;
            }
         }
      }
   }

   // we make a separate pass to expand bits to pixels; for performance,
   // this could run two scanlines behind the above code, so it won't
   // intefere with filtering but will still be in the cache.
   if (depth < 8) {
      for (j=0; j < y; ++j) {
         stbi_uc *cur = a->out + stride*j;
         stbi_uc *in  = a->out + stride*j + x*out_n - img_width_bytes;
         // unpack 1/2/4-bit into a 8-bit buffer. allows us to keep the common 8-bit path optimal at minimal cost for 1/2/4-bit
         // png guarante byte alignment, if width is not multiple of 8/4/2 we'll decode dummy trailing data that will be skipped in the later loop
         stbi_uc scale = (color == 0) ? stbi__depth_scale_table[depth] : 1; // scale grayscale values to 0..255 range

         // note that the final byte might overshoot and write more data than desired.
         // we can allocate enough data that this never writes out of memory, but it
         // could also overwrite the next scanline. can it overwrite non-empty data
         // on the next scanline? yes, consider 1-pixel-wide scanlines with 1-bit-per-pixel.
         // so we need to explicitly clamp the final ones

         if (depth == 4) {
            for (k=x*img_n; k >= 2; k-=2, ++in) {
               *cur++ = scale * ((*in >> 4)       );
               *cur++ = scale * ((*in     ) & 0x0f);
            }
            if (k > 0) *cur++ = scale * ((*in >> 4)       );
         } else if (depth == 2) {
            for (k=x*img_n; k >= 4; k-=4, ++in) {
               *cur++ = scale * ((*in >> 6)       );
               *cur++ = scale * ((*in >> 4) & 0x03);
               *cur++ = scale * ((*in >> 2) & 0x03);
               *cur++ = scale * ((*in     ) & 0x03);
            }
            if (k > 0) *cur++ = scale * ((*in >> 6)       );
            if (k > 1) *cur++ = scale * ((*in >> 4) & 0x03);
            if (k > 2) *cur++ = scale * ((*in >> 2) & 0x03);
         } else if (depth == 1) {
            for (k=x*img_n; k >= 8; k-=8, ++in) {
               *cur++ = scale * ((*in >> 7)       );
               *cur++ = scale * ((*in >> 6) & 0x01);
               *cur++ = scale * ((*in >> 5) & 0x01);
               *cur++ = scale * ((*in >> 4) & 0x01);
               *cur++ = scale * ((*in >> 3) & 0x01);
               *cur++ = scale * ((*in >> 2) & 0x01);
               *cur++ = scale * ((*in >> 1) & 0x01);
               *cur++ = scale * ((*in     ) & 0x01);
            }
            if (k > 0) *cur++ = scale * ((*in >> 7)       );
            if (k > 1) *cur++ = scale * ((*in >> 6) & 0x01);
            if (k > 2) *cur++ = scale * ((*in >> 5) & 0x01);
            if (k > 3) *cur++ = scale * ((*in >> 4) & 0x01);
            if (k > 4) *cur++ = scale * ((*in >> 3) & 0x01);
            if (k > 5) *cur++ = scale * ((*in >> 2) & 0x01);
            if (k > 6) *cur++ = scale * ((*in >> 1) & 0x01);
         }
         if (img_n != out_n) {
            int q;
            // insert alpha = 255
            cur = a->out + stride*j;
            if (img_n == 1) {
               for (q=x-1; q >= 0; --q) {
                  cur[q*2+1] = 255;
                  cur[q*2+0] = cur[q];
               }
            } else {
               STBI_ASSERT(img_n == 3);
               for (q=x-1; q >= 0; --q) {
                  cur[q*4+3] = 255;
                  cur[q*4+2] = cur[q*3+2];
                  cur[q*4+1] = cur[q*3+1];
                  cur[q*4+0] = cur[q*3+0];
               }
            }
         }
      }
   } else if (depth == 16) {
      // force the image data from big-endian to platform-native.
      // this is done in a separate pass due to the decoding relying
      // on the data being untouched, but could probably be done
      // per-line during decode if care is taken.
      stbi_uc *cur = a->out;
      stbi__uint16 *cur16 = (stbi__uint16*)cur;

      for(i=0; i < x*y*out_n; ++i,cur16++,cur+=2) {
         *cur16 = (cur[0] << 8) | cur[1];
      }
   }

   return 1;
}
Unknown