1 files changed, 25 insertions, 1 deletions
diff --git a/src/opengl/qwindowsurface_gl.cpp b/src/opengl/qwindowsurface_gl.cpp
index cd7558c..6185ff8 100644
--- a/src/opengl/qwindowsurface_gl.cpp
+++ b/src/opengl/qwindowsurface_gl.cpp
@@ -285,6 +285,7 @@ struct QGLWindowSurfacePrivate
     int tried_pb : 1;
     int destructive_swap_buffers : 1;
     int geometry_updated : 1;
+    int did_paint : 1;
 
     QGLContext *ctx;
 
@@ -348,6 +349,7 @@ QGLWindowSurface::QGLWindowSurface(QWidget *window)
     d_ptr->glDevice.d = d_ptr;
     d_ptr->q_ptr = this;
     d_ptr->geometry_updated = false;
+    d_ptr->did_paint = false;
 }
 
 QGLWindowSurface::~QGLWindowSurface()
@@ -404,7 +406,18 @@ void QGLWindowSurface::hijackWindow(QWidget *widget)
     if (!d_ptr->fbo && d_ptr->tried_fbo)
         d_ptr->ctx = ctx;
 #else
-    QGLContext *ctx = new QGLContext(surfaceFormat, widget);
+    QGLContext *ctx = NULL;
+
+    // For translucent top-level widgets we need alpha in the format.
+    if (widget->testAttribute(Qt::WA_TranslucentBackground)) {
+        QGLFormat modFormat(surfaceFormat);
+        modFormat.setSampleBuffers(false);
+        modFormat.setSamples(0);
+        modFormat.setAlpha(true);
+        ctx = new QGLContext(modFormat, widget);
+    } else
+        ctx = new QGLContext(surfaceFormat, widget);
+
     ctx->create(qt_gl_share_widget()->context());
 #endif
 
@@ -480,6 +493,8 @@ void QGLWindowSurface::beginPaint(const QRegion &)
         glClearColor(0.0, 0.0, 0.0, 0.0);
         glClear(clearFlags);
     }
+
+    d_ptr->did_paint = true;
 }
 
 void QGLWindowSurface::endPaint(const QRegion &rgn)
@@ -532,6 +547,13 @@ void QGLWindowSurface::flush(QWidget *widget, const QRegion &rgn, const QPoint &
     if (d_ptr->geometry_updated)
         return;
 
+    // did_paint is set to true in ::beginPaint. ::beginPaint means that we
+    // at least cleared the background (= painted something). In EGL API it's a
+    // mistakte to call swapBuffers if nothing was painted. This check protects
+    // the flush func from being executed if it's for nothing.
+    if (!d_ptr->did_paint)
+        return;
+
     QWidget *parent = widget->internalWinId() ? widget : widget->nativeParentWidget();
     Q_ASSERT(parent);
 
@@ -760,6 +782,8 @@ void QGLWindowSurface::flush(QWidget *widget, const QRegion &rgn, const QPoint &
         ctx->swapBuffers();
     else
         glFlush();
+
+    d_ptr->did_paint = false;
 }