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round the alphamul so we don't overflow a byte

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git-svn-id: http://skia.googlecode.com/svn/trunk@1071 2bbb7eff-a529-9590-31e7-b0007b416f81
This commit is contained in:
reed@google.com 2011-04-07 13:31:48 +00:00
parent a076e9be17
commit 3a968750b2
1 changed files with 5 additions and 1 deletions
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6
src/core/SkScan_Antihair.cpp
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@ -670,6 +670,8 @@ void SkScan::AntiFillRect(const SkRect& origR, const SkRegion* clip,
///////////////////////////////////////////////////////////////////////////////
#define SkAlphaMulRound(a, b) SkMulDiv255Round(a, b)
// calls blitRect() if the rectangle is non-empty
static void fillcheckrect(int L, int T, int R, int B, SkBlitter* blitter) {
if (L < R && T < B) {
@ -695,7 +697,9 @@ static inline int FDot8Ceil(FDot8 x) {
// 1 - (1 - a)*(1 - b)
static inline U8CPU InvAlphaMul(U8CPU a, U8CPU b) {
return SkToU8(a + b - SkAlphaMul(a, b));
// need precise rounding (not just SkAlphaMul) so that values like
// a=228, b=252 don't overflow the result
return SkToU8(a + b - SkAlphaMulRound(a, b));
}
static void inner_scanline(FDot8 L, int top, FDot8 R, U8CPU alpha,