Full translucent background support in xcb and xlib backend.

Make sure to pick an alpha visual also for non-GL surface types, and to
ask for alpha in the window format if the WA_TranslucentBackground
attribute is set.

Reviewed-by: Janusz Lewandowski
(cherry picked from commit 6241e39cff9311c943430ff2f31236b13618f2ac)

2 files changed, 18 insertions, 4 deletions

diff --git a/src/plugins/platforms/xlib/qxlibwindow.cpp b/src/plugins/platforms/xlib/qxlibwindow.cpp
index 4efcb1101c..50ea7b58e4 100644
--- a/src/plugins/platforms/xlib/qxlibwindow.cpp
+++ b/src/plugins/platforms/xlib/qxlibwindow.cpp
@@ -81,9 +81,10 @@ QXlibWindow::QXlibWindow(QWidget *window)
     int w = window->width();
     int h = window->height();
 
-    if(window->platformWindowFormat().windowApi() == QPlatformWindowFormat::OpenGL
-            && QApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::OpenGL) ) {
 #if !defined(QT_NO_OPENGL)
+    if(window->platformWindowFormat().windowApi() == QPlatformWindowFormat::OpenGL
+            && QApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::OpenGL)
+            || window->platformWindowFormat().alpha()) {
 #if !defined(QT_OPENGL_ES_2)
         XVisualInfo *visualInfo = qglx_findVisualInfo(mScreen->display()->nativeDisplay(),mScreen->xScreenNumber(),window->platformWindowFormat());
 #else
@@ -117,8 +118,9 @@ QXlibWindow::QXlibWindow(QWidget *window)
         } else {
             qFatal("no window!");
         }
+    } else
 #endif //!defined(QT_NO_OPENGL)
-    } else {
+    {
         mDepth = mScreen->depth();
         mFormat = (mDepth == 32) ? QImage::Format_ARGB32_Premultiplied : QImage::Format_RGB32;
         mVisual = mScreen->defaultVisual();
diff --git a/src/plugins/platforms/xlib/qxlibwindowsurface.cpp b/src/plugins/platforms/xlib/qxlibwindowsurface.cpp
index 78fe387bb8..a917f452e8 100644
--- a/src/plugins/platforms/xlib/qxlibwindowsurface.cpp
+++ b/src/plugins/platforms/xlib/qxlibwindowsurface.cpp
@@ -49,6 +49,8 @@
 #include "qxlibscreen.h"
 #include "qxlibdisplay.h"
 
+#include "qpainter.h"
+
 # include <sys/ipc.h>
 # include <sys/shm.h>
 # include <X11/extensions/XShm.h>
@@ -108,7 +110,7 @@ void QXlibWindowSurface::resizeShmImage(int width, int height)
 
     Q_ASSERT(shm_attach_status == True);
 
-    shm_img = QImage( (uchar*) image->data, image->width, image->height, image->bytes_per_line, QImage::Format_RGB32 );
+    shm_img = QImage( (uchar*) image->data, image->width, image->height, image->bytes_per_line, win->format() );
 #endif
     painted = false;
 }
@@ -213,6 +215,16 @@ void QXlibWindowSurface::beginPaint(const QRegion &region)
 {
     Q_UNUSED(region);
     resizeBuffer(size());
+
+    if (shm_img.hasAlphaChannel()) {
+        QPainter p(&shm_img);
+        p.setCompositionMode(QPainter::CompositionMode_Source);
+        const QVector<QRect> rects = region.rects();
+        const QColor blank = Qt::transparent;
+        for (QVector<QRect>::const_iterator it = rects.begin(); it != rects.end(); ++it) {
+            p.fillRect(*it, blank);
+        }
+    }
 }
 
 void QXlibWindowSurface::endPaint(const QRegion &region)