AuroraMiddleware/qt5base-lts
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Fix accuracy with screen composition

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It was using a faster divide by 256 instead of an accurate divide by
255. This meant black screen wasn't a null operation as it should be.

This also fixes alpha mixing for a few other compositions.

Pick-to: 6.3 6.2 5.15
Fixes: QTBUG-100327
Change-Id: I149ad39147176e00ce753979d55dc8633704dc1a
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
This commit is contained in:
Allan Sandfeld Jensen 2022-02-07 10:48:57 +01:00
parent 94b158134c
commit 2536d73adc
1 changed files with 4 additions and 4 deletions
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8
src/gui/painting/qcompositionfunctions.cpp
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@ -1391,13 +1391,13 @@ private:
static inline int mix_alpha(int da, int sa)
{
return 255 - ((255 - sa) * (255 - da) >> 8);
return 255 - qt_div_255((255 - sa) * (255 - da));
}
#if QT_CONFIG(raster_64bit)
static inline uint mix_alpha_rgb64(uint da, uint sa)
{
return 65535U - ((65535U - sa) * (65535U - da) >> 16);
return 65535U - qt_div_65535((65535U - sa) * (65535U - da));
}
#endif
@ -1807,7 +1807,7 @@ static inline void comp_func_Screen_impl(uint *Q_DECL_RESTRICT dest, const uint
int da = qAlpha(d);
int sa = qAlpha(s);
#define OP(a, b) 255 - (((255-a) * (255-b)) >> 8)
#define OP(a, b) 255 - qt_div_255((255-a) * (255-b))
int r = OP( qRed(d), qRed(s));
int b = OP( qBlue(d), qBlue(s));
int g = OP(qGreen(d), qGreen(s));
@ -1837,7 +1837,7 @@ static inline void comp_func_Screen_impl(QRgba64 *Q_DECL_RESTRICT dest, const QR
uint da = d.alpha();
uint sa = s.alpha();
#define OP(a, b) 65535U - (((65535U-a) * (65535U-b)) >> 16)
#define OP(a, b) 65535U - qt_div_65535((65535U-a) * (65535U-b))
uint r = OP( d.red(), s.red());
uint b = OP( d.blue(), s.blue());
uint g = OP(d.green(), s.green());