implement Qt::TranslucentBackground for Windows

Adapted the Qt 4.8 implementation of translucent widgets in
the Windows platform plugin. This is only working for non-OpenGL
top level Windows.

Change-Id: Ic4c1c52d33b380f530f6a07e96c0c154a0571415
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

3 files changed, 35 insertions, 10 deletions

diff --git a/src/plugins/platforms/windows/qwindowsbackingstore.cpp b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
index 9bd32811a3..a81386d752 100644
--- a/src/plugins/platforms/windows/qwindowsbackingstore.cpp
+++ b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
@@ -80,21 +80,42 @@ void QWindowsBackingStore::flush(QWindow *window, const QRegion &region,
                                         const QPoint &offset)
 {
     Q_ASSERT(window);
-    // TODO: Prepare paint for translucent windows.
+
     const QRect br = region.boundingRect();
     if (QWindowsContext::verboseBackingStore > 1)
         qDebug() << __FUNCTION__ << window << offset << br;
     QWindowsWindow *rw = QWindowsWindow::baseWindowOf(window);
-    const HDC dc = rw->getDC();
-    if (!dc) {
-        qErrnoWarning("%s: GetDC failed", __FUNCTION__);
-        return;
+
+    if (rw->format().hasAlpha() && (window->windowFlags() & Qt::FramelessWindowHint)) {
+        const long wl = GetWindowLong(rw->handle(), GWL_EXSTYLE);
+        if ((wl & WS_EX_LAYERED) == 0)
+            SetWindowLong(rw->handle(), GWL_EXSTYLE, wl | WS_EX_LAYERED);
+
+        QRect r = window->frameGeometry();
+        QPoint frameOffset(window->frameMargins().left(), window->frameMargins().top());
+        QRect dirtyRect = br.translated(offset + frameOffset);
+
+        SIZE size = {r.width(), r.height()};
+        POINT ptDst = {r.x(), r.y()};
+        POINT ptSrc = {0, 0};
+        BLENDFUNCTION blend = {AC_SRC_OVER, 0, (int)(255.0 * rw->opacity()), AC_SRC_ALPHA};
+        RECT dirty = {dirtyRect.x(), dirtyRect.y(),
+            dirtyRect.x() + dirtyRect.width(), dirtyRect.y() + dirtyRect.height()};
+        UPDATELAYEREDWINDOWINFO info = {sizeof(info), NULL, &ptDst, &size, m_image->hdc(), &ptSrc, 0, &blend, ULW_ALPHA, &dirty};
+        QWindowsContext::user32dll.updateLayeredWindowIndirect(rw->handle(), &info);
+    } else {
+        const HDC dc = rw->getDC();
+        if (!dc) {
+            qErrnoWarning("%s: GetDC failed", __FUNCTION__);
+            return;
+        }
+
+        if (!BitBlt(dc, br.x(), br.y(), br.width(), br.height(),
+                    m_image->hdc(), br.x() + offset.x(), br.y() + offset.y(), SRCCOPY))
+            qErrnoWarning("%s: BitBlt failed", __FUNCTION__);
+        rw->releaseDC();
     }
 
-    if (!BitBlt(dc, br.x(), br.y(), br.width(), br.height(),
-                m_image->hdc(), br.x() + offset.x(), br.y() + offset.y(), SRCCOPY))
-        qErrnoWarning("%s: BitBlt failed", __FUNCTION__);
-    rw->releaseDC();
     // Write image for debug purposes.
     if (QWindowsContext::verboseBackingStore > 2) {
         static int n = 0;
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 4e93d2b258..1266004f85 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -647,7 +647,8 @@ QWindowsWindow::QWindowsWindow(QWindow *aWindow, const WindowData &data) :
     m_mouseGrab(false),
     m_cursor(QWindowsScreen::screenOf(aWindow)->windowsCursor()->standardWindowCursor()),
     m_dropTarget(0),
-    m_savedStyle(0)
+    m_savedStyle(0),
+    m_format(aWindow->format())
 #ifdef QT_OPENGL_ES_2
    , m_eglSurface(0)
 #endif
diff --git a/src/plugins/platforms/windows/qwindowswindow.h b/src/plugins/platforms/windows/qwindowswindow.h
index 208c0d2c38..270756d55e 100644
--- a/src/plugins/platforms/windows/qwindowswindow.h
+++ b/src/plugins/platforms/windows/qwindowswindow.h
@@ -142,6 +142,7 @@ public:
     QWindowsWindow(QWindow *window, const WindowData &data);
     ~QWindowsWindow();
 
+    virtual QSurfaceFormat format() const { return m_format; }
     virtual void setGeometry(const QRect &rect);
     virtual QRect geometry() const { return m_data.geometry; }
 
@@ -165,6 +166,7 @@ public:
     virtual QMargins frameMargins() const;
 
     virtual void setOpacity(qreal level);
+    qreal opacity() const { return m_opacity; }
     virtual void requestActivateWindow();
 
     virtual bool setKeyboardGrabEnabled(bool grab);
@@ -254,6 +256,7 @@ private:
     QWindowsOleDropTarget *m_dropTarget;
     unsigned m_savedStyle;
     QRect m_savedFrameGeometry;
+    const QSurfaceFormat m_format;
 #ifdef QT_OPENGL_ES_2
     EGLSurface m_eglSurface;
     QSharedPointer<QWindowsEGLStaticContext> m_staticEglContext;