commit ad1f69d28d31725a22e7e1cbb4d950aa9ad3bea7
author Thorsten Behrens <thorsten.behrens@allotropia.de> Sun Aug 06 01:19:17 2023 +0200
committer Noel Grandin <noel.grandin@collabora.co.uk> Sun Aug 06 12:23:07 2023 +0200
tree f3c553d612f3db55d778ac5835bd1938799d7173
parent f454a774053d2f631009612c78713822f6afdbd2

tdf#156540 invert alpha mask when drawing sprites

Due to the switch from transparency to alpha in commit
81994cb2b8b32453a92bcb011830fcb884f22ff3, 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
81994cb2b8b32453a92bcb011830fcb884f22ff3.

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>

canvas/source/vcl/spritehelper.cxx

diff --git a/canvas/source/vcl/spritehelper.cxx b/canvas/source/vcl/spritehelper.cxx
index 3494a5f..f188526 100644
--- a/canvas/source/vcl/spritehelper.cxx
+++ b/canvas/source/vcl/spritehelper.cxx
@@ -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 );
            }
        }

vcl/source/bitmap/alpha.cxx

diff --git a/vcl/source/bitmap/alpha.cxx b/vcl/source/bitmap/alpha.cxx
index 8e082c6..ff0d035 100644
--- a/vcl/source/bitmap/alpha.cxx
+++ b/vcl/source/bitmap/alpha.cxx
@@ -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;
        }