Alexandre Julliard : gdi32: Avoid having the source alpha channel interfere with color comparisons in GdiTransparentBlt.

[Alexandre Julliard]

Module: wine
Branch: master
Commit: 474f9ff1fa2ebf4ae6c4ef3b0d4987062b30d838
URL:    http://source.winehq.org/git/wine.git/?a=commit;h=474f9ff1fa2ebf4ae6c4ef3b0d...

Author: Alexandre Julliard <julliard(a)winehq.org>
Date:   Wed Jul 12 11:43:50 2017 +0200

gdi32: Avoid having the source alpha channel interfere with color comparisons in GdiTransparentBlt.

Signed-off-by: Alexandre Julliard <julliard(a)winehq.org>

---

 dlls/gdi32/bitblt.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/dlls/gdi32/bitblt.c b/dlls/gdi32/bitblt.c
index 3d8c128..1b057f7 100644
--- a/dlls/gdi32/bitblt.c
+++ b/dlls/gdi32/bitblt.c
@@ -857,7 +857,19 @@ BOOL WINAPI GdiTransparentBlt( HDC hdcDest, int xDest, int yDest, int widthDest,
     if(oldStretchMode == BLACKONWHITE || oldStretchMode == WHITEONBLACK)
         SetStretchBltMode(hdcSrc, COLORONCOLOR);
     hdcWork = CreateCompatibleDC(hdcDest);
-    bmpWork = CreateCompatibleBitmap(hdcDest, widthDest, heightDest);
+    if (GetObjectType( hdcDest ) != OBJ_MEMDC && GetDeviceCaps( hdcDest, BITSPIXEL ) == 32)
+    {
+        /* screen DCs are not supposed to have an alpha channel, so use a 24-bpp bitmap as copy */
+        BITMAPINFO info;
+        info.bmiHeader.biSize = sizeof(info.bmiHeader);
+        info.bmiHeader.biWidth = widthDest;
+        info.bmiHeader.biHeight = heightDest;
+        info.bmiHeader.biPlanes = 1;
+        info.bmiHeader.biBitCount = 24;
+        info.bmiHeader.biCompression = BI_RGB;
+        bmpWork = CreateDIBSection( 0, &info, DIB_RGB_COLORS, NULL, NULL, 0 );
+    }
+    else bmpWork = CreateCompatibleBitmap(hdcDest, widthDest, heightDest);
     oldWork = SelectObject(hdcWork, bmpWork);
     if(!StretchBlt(hdcWork, 0, 0, widthDest, heightDest, hdcSrc, xSrc, ySrc, widthSrc, heightSrc, SRCCOPY)) {
         TRACE("Failed to stretch\n");