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Lua: fix alpha-blending, use safer 16-bit color decomposition

This commit is contained in:
gocha 2012-08-12 19:30:12 +09:00
parent 224606757d
commit 82d02837d7
1 changed files with 10 additions and 8 deletions
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18
lua-engine.cpp
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@ -2543,10 +2543,10 @@ DEFINE_LUA_FUNCTION(gui_parsecolor, "color")
static inline void blend32(uint32 *dstPixel, uint32 color)
{
uint8 *dst = (uint8*) dstPixel;
int r = (color & 0xFF000000) >> 24;
int g = (color & 0x00FF0000) >> 16;
int b = (color & 0x0000FF00) >> 8;
int a = color & 0x000000FF;
uint8 r = (color & 0xFF000000) >> 24;
uint8 g = (color & 0x00FF0000) >> 16;
uint8 b = (color & 0x0000FF00) >> 8;
uint8 a = color & 0x000000FF;
if (a == 255) {
// direct copy
@ -2560,14 +2560,16 @@ static inline void blend32(uint32 *dstPixel, uint32 color)
}
else {
// alpha-blending
// http://en.wikipedia.org/wiki/Alpha_compositing
uint8 bo = dst[0];
uint8 go = dst[1];
uint8 ro = dst[2];
uint8 ao = dst[3];
dst[0] = (((b - bo) * a + (bo << 8)) >> 8);
dst[1] = (((g - go) * a + (go << 8)) >> 8);
dst[2] = (((r - ro) * a + (ro << 8)) >> 8);
dst[3] = ((a + ao) - ((a * ao + 0xFF) >> 8));
uint8 aof = (ao * (255 - a)) / 255;
dst[3] = a + aof;
dst[0] = (b * a + bo * aof) / dst[3];
dst[1] = (g * a + go * aof) / dst[3];
dst[2] = (r * a + ro * aof) / dst[3];
}
}