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Bug 1171454 - Workaround for Cairo's source operator with alpha handling. r=jrmuizel

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--HG--
extra : rebase_source : 12d68416660935bf2072a898c903f29b80c39107
This commit is contained in:
Lee Salzman 2015-06-05 15:30:13 -04:00
parent 79c10f9f1d
commit cb8cec408b
1 changed files with 23 additions and 5 deletions
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28
gfx/2d/DrawTargetCairo.cpp
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@ -722,6 +722,27 @@ DrawTargetCairo::GetDummySurface()
return mDummySurface;
}
static void
PaintWithAlpha(cairo_t* aContext, const DrawOptions& aOptions)
{
if (aOptions.mCompositionOp == CompositionOp::OP_SOURCE) {
// Cairo treats the source operator like a lerp when alpha is < 1.
// Approximate the desired operator by: out = 0; out += src*alpha;
if (aOptions.mAlpha == 1) {
cairo_set_operator(aContext, CAIRO_OPERATOR_SOURCE);
cairo_paint(aContext);
} else {
cairo_set_operator(aContext, CAIRO_OPERATOR_CLEAR);
cairo_paint(aContext);
cairo_set_operator(aContext, CAIRO_OPERATOR_ADD);
cairo_paint_with_alpha(aContext, aOptions.mAlpha);
}
} else {
cairo_set_operator(aContext, GfxOpToCairoOp(aOptions.mCompositionOp));
cairo_paint_with_alpha(aContext, aOptions.mAlpha);
}
}
void
DrawTargetCairo::DrawSurface(SourceSurface *aSurface,
const Rect &aDest,
@ -770,9 +791,7 @@ DrawTargetCairo::DrawSurface(SourceSurface *aSurface,
cairo_set_source(mContext, pat);
}
cairo_set_operator(mContext, GfxOpToCairoOp(aOptions.mCompositionOp));
cairo_paint_with_alpha(mContext, aOptions.mAlpha);
PaintWithAlpha(mContext, aOptions);
cairo_pattern_destroy(pat);
}
@ -904,8 +923,7 @@ DrawTargetCairo::DrawPattern(const Pattern& aPattern,
cairo_pop_group_to_source(mContext);
// Now draw the content using the desired operator
cairo_set_operator(mContext, GfxOpToCairoOp(aOptions.mCompositionOp));
cairo_paint_with_alpha(mContext, aOptions.mAlpha);
PaintWithAlpha(mContext, aOptions);
} else {
cairo_set_operator(mContext, GfxOpToCairoOp(aOptions.mCompositionOp));