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Avoid 32-bit integer overflow in median cut algorithm (fix #727)

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This fixes a problem generating invalid RGBA entries for an optimized
palette. (E.g. Generating non-opaque pixels when we feed the algorithm
only with opaque pixels.)
This commit is contained in:
David Capello 2015-07-23 09:05:48 -03:00
parent dd0a6d6a40
commit ce7c34bb72
1 changed files with 13 additions and 5 deletions
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18
src/render/median_cut.h
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@ -117,11 +117,19 @@ namespace render {
if (count == 0)
return doc::rgba(0, 0, 0, 255);
// Returns the mean.
return doc::rgba((255 * r / (Histogram::RElements-1)) / count,
(255 * g / (Histogram::GElements-1)) / count,
(255 * b / (Histogram::BElements-1)) / count,
(255 * a / (Histogram::AElements-1)) / count);
// Calculate the mean. We have to do this before the *255
// multiplication to avoid a 32-bit overflow. E.g. Alpha channel
// is the most proper to overflow the 32-bit capacity in case
// all pixels are opaque.
r /= count;
g /= count;
b /= count;
a /= count;
return doc::rgba((255 * r / (Histogram::RElements-1)),
(255 * g / (Histogram::GElements-1)),
(255 * b / (Histogram::BElements-1)),
(255 * a / (Histogram::AElements-1)));
}
// The boxes will be sort in the priority_queue by volume.