winex11: Force alpha channel to 0 when blitting to depth 32 from a lower depth.

dlls/winex11.drv/xrender.c

@@ -603,6 +603,32 @@ static Picture get_xrender_picture_source(X11DRV_PDEVICE *physDev, BOOL repeat)
     return info->pict_src;
 }
 
+/* return a mask picture used to force alpha to 0 */
+static Picture get_no_alpha_mask(void)
+{
+    static Pixmap pixmap;
+    static Picture pict;
+
+    wine_tsx11_lock();
+    if (!pict)
+    {
+        const WineXRenderFormat *fmt = get_xrender_format( WXR_FORMAT_A8R8G8B8 );
+        XRenderPictureAttributes pa;
+        XRenderColor col;
+
+        pixmap = XCreatePixmap( gdi_display, root_window, 1, 1, 32 );
+        pa.repeat = RepeatNormal;
+        pa.component_alpha = True;
+        pict = pXRenderCreatePicture( gdi_display, pixmap, fmt->pict_format,
+                                      CPRepeat|CPComponentAlpha, &pa );
+        col.red = col.green = col.blue = 0xffff;
+        col.alpha = 0;
+        pXRenderFillRectangle( gdi_display, PictOpSrc, pict, &col, 0, 0, 1, 1 );
+    }
+    wine_tsx11_unlock();
+    return pict;
+}
+
 static BOOL fontcmp(LFANDSIZE *p1, LFANDSIZE *p2)
 {
   if(p1->hash != p2->hash) return TRUE;
@@ -2285,6 +2311,7 @@ BOOL X11DRV_XRender_GetSrcAreaStretch(X11DRV_PDEVICE *physDevSrc, X11DRV_PDEVICE
     }
     else /* color -> color (can be at different depths) or mono -> mono */
     {
+        if (physDevDst->depth == 32 && physDevSrc->depth < 32) mask_pict = get_no_alpha_mask();
         src_pict = get_xrender_picture_source( physDevSrc, use_repeat );
 
         wine_tsx11_lock();
@@ -2292,7 +2319,8 @@ BOOL X11DRV_XRender_GetSrcAreaStretch(X11DRV_PDEVICE *physDevSrc, X11DRV_PDEVICE
                                           pixmap, dst_format->pict_format,
                                           CPSubwindowMode|CPRepeat, &pa);
 
-        xrender_blit(PictOpSrc, src_pict, 0, dst_pict, x_src, y_src, 0, 0, xscale, yscale, width, height);
+        xrender_blit(PictOpSrc, src_pict, mask_pict, dst_pict,
+                     x_src, y_src, 0, 0, xscale, yscale, width, height);
 
         if(dst_pict) pXRenderFreePicture(gdi_display, dst_pict);
         wine_tsx11_unlock();