Fall back to pixmaps in xp style when toplevel is translucent

The "fast path" will write bad premlutiplied pixels into the
backbuffer so the blending will be broken, plus that the window
does not get mouse events for alpha=0 pixels.

Reviewed-by: Marius Storm-Olsen

1 files changed, 10 insertions, 1 deletions

diff --git a/src/gui/styles/qwindowsxpstyle.cpp b/src/gui/styles/qwindowsxpstyle.cpp
index 0dc1832..9c374d8 100644
--- a/src/gui/styles/qwindowsxpstyle.cpp
+++ b/src/gui/styles/qwindowsxpstyle.cpp
@@ -621,12 +621,21 @@ void QWindowsXPStylePrivate::drawBackground(XPThemeData &themeData)
     QMatrix m = painter->matrix();
     bool complexXForm = m.m11() != 1.0 || m.m22() != 1.0 || m.m12() != 0.0 || m.m21() != 0.0;
 
+    bool translucentToplevel = false;
+    QPaintDevice *pdev = painter->device();
+    if (pdev->devType() == QInternal::Widget) {
+        QWidget *win = ((QWidget *) pdev)->window();
+        translucentToplevel = win->testAttribute(Qt::WA_TranslucentBackground);
+    }
+
     bool useFallback = painter->paintEngine()->getDC() == 0
                        || painter->opacity() != 1.0
                        || themeData.rotate
                        || complexXForm
                        || themeData.mirrorVertically
-                       || (themeData.mirrorHorizontally && pDrawThemeBackgroundEx == 0);
+                       || (themeData.mirrorHorizontally && pDrawThemeBackgroundEx == 0)
+                       || translucentToplevel;
+
     if (!useFallback)
         drawBackgroundDirectly(themeData);
     else