Make translucent windows work, and support WA_TranslucentBackground

QWS will make a window translucent if the background brush is not
opaque. Now we also support the cross-platform way of doing it.
This also includes fixes for bugs caused by behavioural changes in
the internal windowsurface/backingstore implementation.

Task-number: QTBUG-5739
Reviewed-by: Tom

3 files changed, 28 insertions, 2 deletions

diff --git a/src/gui/painting/qbackingstore.cpp b/src/gui/painting/qbackingstore.cpp
index c73d9f4..8de9eaa 100644
--- a/src/gui/painting/qbackingstore.cpp
+++ b/src/gui/painting/qbackingstore.cpp
@@ -352,6 +352,10 @@ void QWidgetBackingStore::beginPaint(QRegion &toClean, QWidget *widget, QWindowS
     // Always flush repainted areas.
     dirtyOnScreen += toClean;
 
+#ifdef Q_WS_QWS
+    toClean.translate(tlwOffset);
+#endif
+
 #ifdef QT_NO_PAINT_DEBUG
     windowSurface->beginPaint(toClean);
 #else
@@ -766,7 +770,12 @@ void QWidgetBackingStore::paintWindowDecoration()
     if (decorationRegion.isEmpty())
         return;
 
-    windowSurface->beginPaint(decorationRegion);
+    //### The QWS decorations do not always paint the pixels they promise to paint.
+    // This causes painting problems with QWSMemorySurface. Since none of the other
+    // window surfaces actually use the region, passing an empty region is a safe
+    // workaround.
+
+    windowSurface->beginPaint(QRegion());
 
     QPaintEngine *engine = windowSurface->paintDevice()->paintEngine();
     Q_ASSERT(engine);
diff --git a/src/gui/painting/qwindowsurface_qws.cpp b/src/gui/painting/qwindowsurface_qws.cpp
index d3fc9de..a816ed2 100644
--- a/src/gui/painting/qwindowsurface_qws.cpp
+++ b/src/gui/painting/qwindowsurface_qws.cpp
@@ -80,7 +80,7 @@ static void qt_insertWindowSurface(int winId, QWSWindowSurface *surface)
 
 inline bool isWidgetOpaque(const QWidget *w)
 {
-    return w->d_func()->isOpaque;
+    return w->d_func()->isOpaque && !w->testAttribute(Qt::WA_TranslucentBackground);
 }
 
 static inline QScreen *getScreen(const QWidget *w)
@@ -873,6 +873,21 @@ bool QWSMemorySurface::isValid() const
     return true;
 }
 
+// ### copied from qwindowsurface_raster.cpp -- should be cross-platform
+void QWSMemorySurface::beginPaint(const QRegion &rgn)
+{
+    if (!isWidgetOpaque(window())) {
+        QPainter p(&img);
+        p.setCompositionMode(QPainter::CompositionMode_Source);
+        const QVector<QRect> rects = rgn.rects();
+        const QColor blank = Qt::transparent;
+        for (QVector<QRect>::const_iterator it = rects.begin(); it != rects.end(); ++it) {
+            p.fillRect(*it, blank);
+        }
+    }
+    QWSWindowSurface::beginPaint(rgn);
+}
+
 // from qwindowsurface.cpp
 extern void qt_scrollRectInImage(QImage &img, const QRect &rect, const QPoint &offset);
 
diff --git a/src/gui/painting/qwindowsurface_qws_p.h b/src/gui/painting/qwindowsurface_qws_p.h
index a8371c8..30900dc 100644
--- a/src/gui/painting/qwindowsurface_qws_p.h
+++ b/src/gui/painting/qwindowsurface_qws_p.h
@@ -176,6 +176,8 @@ public:
     QImage image() const { return img; }
     QPoint painterOffset() const;
 
+    void beginPaint(const QRegion &rgn);
+
     bool lock(int timeout = -1);
     void unlock();