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GRAPHICS: Fix computation of addA in darkenFill()

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The old computation had rounding issues, causing alpha to leak into
the red (usually) component.  There's a much easier way to compute it
that does not lead to such problems:  What should really happen is that
the two top bits of the A component should be set to 1 (thus adding
75% alpha).  So compute it that way for speed and precision.
This commit is contained in:
Marcus Comstedt 2014-01-10 15:45:37 +01:00
parent 66ad9e76ee
commit 51d7405a7b
1 changed files with 1 additions and 2 deletions
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3
graphics/VectorRendererSpec.cpp
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@ -691,8 +691,7 @@ darkenFill(PixelType *ptr, PixelType *end) {
// assuming at least 3 alpha bits
mask |= 3 << _format.aShift;
PixelType addA = (PixelType)(255 >> _format.aLoss) << _format.aShift;
addA -= (addA >> 2);
PixelType addA = (PixelType)(3 << (_format.aShift + 6 - _format.aLoss));
while (ptr != end) {
// Darken the colour, and increase the alpha