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tdf#156540 invert alpha mask when drawing sprites

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Due to the switch from transparency to alpha in commit
81994cb2b8, a sprite's
alpha mask needs to be inverted.

Additionally, fixes an oversight in vcl's alpha.cxx, where manual
blend math got mangled, also in
81994cb2b8.

Change-Id: I8ebbbc7fe624d8dfc8121d8814d30875c498870d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/155378
Reviewed-by: Patrick Luby <plubius@neooffice.org>
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
This commit is contained in:
Thorsten Behrens 2023-08-06 01:19:17 +02:00 committed by Noel Grandin
parent f454a77405
commit ad1f69d28d
2 changed files with 6 additions and 4 deletions
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6
canvas/source/vcl/spritehelper.cxx
View file

@ -134,12 +134,14 @@ namespace vclcanvas
// sprite content might contain alpha, create
// BmpEx, then.
BitmapEx aMask( mpBackBufferMask->getOutDev().GetBitmapEx( aEmptyPoint,
aOutputSize ) );
aOutputSize ) );
AlphaMask aAlpha( aMask.GetBitmap() );
aAlpha.Invert();
// Note: since we retrieved aBmp and aMask
// directly from an OutDev, it's already a
// 'display bitmap' on windows.
maContent = BitmapEx( aBmp.GetBitmap(), AlphaMask( aMask.GetBitmap()) );
maContent = BitmapEx( aBmp.GetBitmap(), aAlpha );
}
}

4
vcl/source/bitmap/alpha.cxx
View file

@ -118,8 +118,8 @@ void AlphaMask::BlendWith(const AlphaMask& rOther)
// Awkward calculation because the original used transparency, and to replicate
// the logic we need to translate into transparency, perform the original logic,
// then translate back to alpha.
auto tmp = 255 - ((255 - nGrey1) + (255 - nGrey2) - (255 - nGrey1) * (255 - nGrey2));
*scanline = static_cast<sal_uInt8>(tmp / 255);
auto tmp = 255 - ((255 - nGrey1) + (255 - nGrey2) - (255 - nGrey1) * (255 - nGrey2) / 255);
*scanline = static_cast<sal_uInt8>(tmp);
++scanline;
++otherScanline;
}