modules/gui/qt/maininterface/compositor_x11_renderwindow.cpp

@@ -395,7 +395,7 @@ bool CompositorX11RenderWindow::startRendering()
     m_renderTask->moveToThread(m_renderThread);
     connect(m_renderThread, &QThread::finished, m_renderTask, &QObject::deleteLater);
 
-    connect(m_interfaceWindow, &CompositorX11UISurface::afterRendering, m_renderTask, &RenderTask::requestRefresh);
+    connect(m_interfaceWindow, &CompositorX11UISurface::updated, m_renderTask, &RenderTask::requestRefresh);
     connect(m_interfaceWindow, &CompositorX11UISurface::sizeChanged, m_renderTask, &RenderTask::onInterfaceSizeChanged);
 
     connect(this, &CompositorX11RenderWindow::windowSizeChanged, m_renderTask, &RenderTask::onWindowSizeChanged);

modules/gui/qt/maininterface/compositor_x11_uisurface.cpp

@@ -37,6 +37,10 @@ CompositorX11UISurface::CompositorX11UISurface(QWindow* window, QScreen* screen)
     format.setStencilBufferSize(8);
     format.setAlphaBufferSize(8);
     format.setSwapInterval(0);
+
+    // UI is renderred on offscreen, no need for double bufferring
+    format.setSwapBehavior(QSurfaceFormat::SingleBuffer);
+
     setFormat(format);
 
     m_context = new QOpenGLContext();
@@ -133,13 +137,15 @@ void CompositorX11UISurface::render()
     m_uiRenderControl->polishItems();
     m_uiRenderControl->sync();
 
-    // FIXME: Render function should be executed in rendering thread
+    // TODO: investigate multithreaded renderer
     m_uiRenderControl->render();
 
     m_uiWindow->resetOpenGLState();
 
     m_context->functions()->glFlush();
     m_context->swapBuffers(this);
+
+    emit updated();
 }
 
 void CompositorX11UISurface::updateSizes()

modules/gui/qt/maininterface/compositor_x11_uisurface.hpp

@@ -64,6 +64,7 @@ signals:
     void beforeRendering();
     void afterRendering();
     void sizeChanged(const QSize& size);
+    void updated();
 
 protected:
     bool event(QEvent *event) override;