[PATCH v2 0/1] MR8988: win32u: change the stretch mode of dst hdc from BlackOnWhite to ColorOnColor...

[Kun Yang (＠yangkun)]

win32u: change the stretch mode of dst hdc from BlackOnWhite to ColorOnColor when using StretchBlt in TransparentBlt.

In NtGdiTransparentBlt function, the StretchBlt mode of dst hdc is not set. The Default StretchBlt Mode in wine is BlackOnWhite. It is not correct to use this StretchBltMode in TransparentBlt dealing with color bitmap. According to MSDN, it should be converted to ColorOnColor.
My test code shows that, the image converted by wine generates a lot of chromatic noise.

[test_blt.c](/uploads/26101bc7bdb27400d02c8ff5bf741864/test_blt.c)

[test_blt.exe](/uploads/98ee3ab7ce0d590e1511bd8a5fb5a1bb/test_blt.exe)

![source](/uploads/0c56c5e6d1280040ba08cd3dee7acd95/source.bmp)

![result_wrong](/uploads/2076396e069f852914313a8fb86dd5e2/result_wrong.bmp)

![result](/uploads/cf3ec00bf0f0e7f3ea7fe1e2085385d6/result.bmp)

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  v2: win32u: change the stretch mode of dst hdc from BlackOnWhite to ColorOnColor when using StretchBlt in TransparentBlt.

https://gitlab.winehq.org/wine/wine/-/merge_requests/8988