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stb_image_write: fix indexing error when computing PNG filters with the stbi__flip_vertically_on_write on.

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The PNG filters of the pixels row N are computed using row N-1 of the final image. If the image should be flipped when saving, this corresponds to row N+1 of the initial image.
master
Simon Rodriguez ago%!(EXTRA string=7 years)
parent 73990fefe7
commit 34f087ce4c
1 changed files with 7 additions and 6 deletions
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  1. 13
      stb_image_write.h

13
stb_image_write.h
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@ -987,13 +987,14 @@ static void stbiw__encode_png_line(unsigned char *pixels, int stride_bytes, int
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;
for (i = 0; i < n; ++i) {
switch (type) {
case 0: line_buffer[i] = z[i]; break;
case 1: line_buffer[i] = z[i]; break;
case 2: line_buffer[i] = z[i] - z[i-stride_bytes]; break;
case 3: line_buffer[i] = z[i] - (z[i-stride_bytes]>>1); break;
case 4: line_buffer[i] = (signed char) (z[i] - stbiw__paeth(0,z[i-stride_bytes],0)); 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;
}
@ -1002,9 +1003,9 @@ static void stbiw__encode_png_line(unsigned char *pixels, int stride_bytes, int
switch (type) {
case 0: line_buffer[i] = z[i]; break;
case 1: line_buffer[i] = z[i] - z[i-n]; break;
case 2: line_buffer[i] = z[i] - z[i-stride_bytes]; break;
case 3: line_buffer[i] = z[i] - ((z[i-n] + z[i-stride_bytes])>>1); break;
case 4: line_buffer[i] = z[i] - stbiw__paeth(z[i-n], z[i-stride_bytes], z[i-stride_bytes-n]); break;
case 2: line_buffer[i] = z[i] - z[i-signed_stride]; break;
case 3: line_buffer[i] = z[i] - ((z[i-n] + z[i-signed_stride])>>1); break;
case 4: line_buffer[i] = z[i] - stbiw__paeth(z[i-n], z[i-signed_stride], z[i-signed_stride-n]); break;
case 5: line_buffer[i] = z[i] - (z[i-n]>>1); break;
case 6: line_buffer[i] = z[i] - stbiw__paeth(z[i-n], 0,0); break;
}

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