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sw_engine common: improving the alpha blending algorithm

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Calculations accuracy in ALPHA_BLEND function has been
improved. Until now blending resulted in a slight hue change
(all color channels affected). The chosen method of calculation
is a compromise between the accuracy and the performance.
This commit is contained in:
Mira Grudzinska 2021-06-02 14:01:12 +02:00 • committed by GitHub
parent c7a156d5a6
commit 6ccebb3234
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 2 additions and 2 deletions
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4
src/lib/sw_engine/tvgSwCommon.h
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@ -268,8 +268,8 @@ static inline SwCoord TO_SWCOORD(float val)
static inline uint32_t ALPHA_BLEND(uint32_t c, uint32_t a)
{
return (((((c >> 8) & 0x00ff00ff) * a) & 0xff00ff00) +
((((c & 0x00ff00ff) * a) >> 8) & 0x00ff00ff));
return (((((c >> 8) & 0x00ff00ff) * a + 0x00ff00ff) & 0xff00ff00) +
((((c & 0x00ff00ff) * a + 0x00ff00ff) >> 8) & 0x00ff00ff));
}
static inline uint32_t COLOR_INTERPOLATE(uint32_t c1, uint32_t a1, uint32_t c2, uint32_t a2)