diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/gui/painting/qdrawhelper_p.h | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/src/gui/painting/qdrawhelper_p.h b/src/gui/painting/qdrawhelper_p.h index 3c945338a6..0f98b07229 100644 --- a/src/gui/painting/qdrawhelper_p.h +++ b/src/gui/painting/qdrawhelper_p.h @@ -699,7 +699,8 @@ static Q_ALWAYS_INLINE uint INV_PREMUL(uint p) { return 0; // (p*(0x00ff00ff/alpha)) >> 16 == (p*255)/alpha for all p and alpha <= 256. const uint invAlpha = 0x00ff00ffU / alpha; - return qRgba((qRed(p)*invAlpha)>>16, (qGreen(p)*invAlpha)>>16, (qBlue(p)*invAlpha)>>16, alpha); + // We add 0x8000 to get even rounding. The rounding also ensures that PREMUL(INV_PREMUL(p)) == p for all p. + return qRgba((qRed(p)*invAlpha + 0x8000)>>16, (qGreen(p)*invAlpha + 0x8000)>>16, (qBlue(p)*invAlpha + 0x8000)>>16, alpha); } struct quint24 { |