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)

1 files changed, 2 insertions, 0 deletions

diff --git a/src/opengl/qgl_qpa.cpp b/src/opengl/qgl_qpa.cpp
index 994344c6eb..9da650f98d 100644
--- a/src/opengl/qgl_qpa.cpp
+++ b/src/opengl/qgl_qpa.cpp
@@ -150,6 +150,8 @@ bool QGLContext::chooseContext(const QGLContext* shareContext)
             if (shareContext) {
                 winFormat.setSharedContext(shareContext->d_func()->platformContext);
             }
+            if (widget->testAttribute(Qt::WA_TranslucentBackground))
+                winFormat.setAlpha(true);
             winFormat.setWindowApi(QPlatformWindowFormat::OpenGL);
             winFormat.setWindowSurface(false);
             widget->setPlatformWindowFormat(winFormat);