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Correct alpha blending in PDF plot 

We fake the alpha channel by pre-multiplying but we forgot to account
for the downscaling of the input channel value in addition to correcting
the alpha * white.  This led to clipping when the values overflowed

Fixes https://gitlab.com/kicad/code/kicad/issues/14238

(cherry picked from commit d405fff1d8)
This commit is contained in:
Seth Hillbrand 2023-03-10 08:35:18 -08:00
parent d5bf831f60
commit bff2f53996
1 changed files with 5 additions and 4 deletions
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9
common/plotters/PDF_plotter.cpp
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@ -513,10 +513,11 @@ void PDF_PLOTTER::PlotImage( const wxImage& aImage, const VECTOR2I& aPos, double
if( alpha < 0xFF )
{
float a = 1.0 - ( (float) alpha / 255.0 );
r = ( int )( r + ( a * 0xFF ) ) & 0xFF;
g = ( int )( g + ( a * 0xFF ) ) & 0xFF;
b = ( int )( b + ( a * 0xFF ) ) & 0xFF;
float d = alpha / 255.0;
float a = 1.0 - d;
r = std::min( KiROUND( r * d + ( a * 0xFF ) ), 0xFF );
g = std::min( KiROUND( g * d + ( a * 0xFF ) ), 0xFF );
b = std::min( KiROUND( b * d + ( a * 0xFF ) ), 0xFF );
}
}