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Fix alpha blending

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- "/ 257", because 255 * 257 = UINT16_MAX
- "/ 255", because that's the maximum possible RGB value
This commit is contained in:
FRIGN
2016-01-31 11:05:00 +01:00
committed by Markus Teich
parent b0ad67036e
commit 68ac6486b1
1 changed files with 7 additions and 7 deletions
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14
sent.c
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@ -258,15 +258,15 @@ int ffread(Image *img)
nbytes += count; nbytes += count;
} }
for (x = 0; x < rowlen / 2; x += 4) { for (x = 0; x < rowlen / 2; x += 4) {
fg_r = ntohs(row[x + 0]) / 256; fg_r = ntohs(row[x + 0]) / 257;
fg_g = ntohs(row[x + 1]) / 256; fg_g = ntohs(row[x + 1]) / 257;
fg_b = ntohs(row[x + 2]) / 256; fg_b = ntohs(row[x + 2]) / 257;
opac = ntohs(row[x + 3]) / 256; opac = ntohs(row[x + 3]) / 257;
/* blend opaque part of image data with window background color to /* blend opaque part of image data with window background color to
* emulate transparency */ * emulate transparency */
img->buf[off++] = (fg_r * opac + bg_r * (255 - opac)) / 256; img->buf[off++] = (fg_r * opac + bg_r * (255 - opac)) / 255;
img->buf[off++] = (fg_g * opac + bg_g * (255 - opac)) / 256; img->buf[off++] = (fg_g * opac + bg_g * (255 - opac)) / 255;
img->buf[off++] = (fg_b * opac + bg_b * (255 - opac)) / 256; img->buf[off++] = (fg_b * opac + bg_b * (255 - opac)) / 255;
} }
} }