uxtheme: Do not transfer glyph alpha values when drawing opaque background.

dlls/uxtheme/draw.c

@@ -523,6 +523,39 @@ static inline void get_transparency (HTHEME hTheme, int iPartId, int iStateId,
     }
 }
 
+/* Reset alpha values in hdc to 0xFF if the background is opaque */
+static void reset_dc_alpha_values(HTHEME htheme, HDC hdc, int part_id, int state_id,
+                                  const RECT *rect)
+{
+    static const RGBQUAD bitmap_bits = {0x0, 0x0, 0x0, 0xFF};
+    BITMAPINFO bitmap_info = {{0}};
+    RECT image_rect;
+    BOOL has_alpha;
+    HBITMAP hbmp;
+    int bg_type;
+
+    if (GetDeviceCaps(hdc, BITSPIXEL) != 32)
+        return;
+
+    if (FAILED(GetThemeEnumValue(htheme, part_id, state_id, TMT_BGTYPE, &bg_type))
+        || bg_type != BT_IMAGEFILE)
+        return;
+
+    if (FAILED(UXTHEME_LoadImage(htheme, part_id, state_id, rect, FALSE, &hbmp, &image_rect,
+                                 &has_alpha, NULL)) || has_alpha)
+        return;
+
+    bitmap_info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
+    bitmap_info.bmiHeader.biWidth = 1;
+    bitmap_info.bmiHeader.biHeight = 1;
+    bitmap_info.bmiHeader.biPlanes = 1;
+    bitmap_info.bmiHeader.biBitCount = 32;
+    bitmap_info.bmiHeader.biCompression = BI_RGB;
+    StretchDIBits(hdc, rect->left, rect->top, abs(rect->right - rect->left),
+                  abs(rect->bottom - rect->top), 0, 0, 1, 1, &bitmap_bits, &bitmap_info,
+                  DIB_RGB_COLORS, SRCPAINT);
+}
+
 /***********************************************************************
  *      UXTHEME_DrawImageGlyph
  *
@@ -581,6 +614,11 @@ static HRESULT UXTHEME_DrawImageGlyph(HTHEME hTheme, HDC hdc, int iPartId,
 
     SelectObject(hdcSrc, oldSrc);
     DeleteDC(hdcSrc);
+
+    /* Don't transfer alpha values from the glyph when drawing opaque background */
+    if (SUCCEEDED(hr) && hasAlpha)
+        reset_dc_alpha_values(hTheme, hdc, iPartId, iStateId, pRect);
+
     return hr;
 }
 

dlls/uxtheme/tests/system.c

@@ -2322,7 +2322,6 @@ static void test_DrawThemeBackgroundEx(void)
 
         ptr += 4;
     }
-    todo_wine
     ok(i == width * height || broken(ptr[3] == 0) /* Spin button glyphs on XP don't use alpha */,
        "Unexpected alpha value %#x at (%d,%d).\n", ptr[3], i % height, i / height);