Drop the explicit fallback to XRender

Summary:
With the new try of all compositor types supported there is an automatic
fallback from OpenGL to XRender/QPainter in case OpenGL setup failed.
So there is no need to invoke a method to do just that.

Reviewers: #kwin, #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D8364

composite.cpp

@@ -477,17 +477,6 @@ void Compositor::deleteUnusedSupportProperties()
     }
 }
 
-// OpenGL self-check failed, fallback to XRender
-void Compositor::fallbackToXRenderCompositing()
-{
-    finish();
-    KConfigGroup config(kwinApp()->config(), "Compositing");
-    config.writeEntry("Backend", "XRender");
-    config.sync();
-    options->setCompositingMode(XRenderCompositing);
-    setup();
-}
-
 void Compositor::slotConfigChanged()
 {
     if (!m_suspended) {

composite.h

@@ -193,7 +193,6 @@ private Q_SLOTS:
      * That is the Compositor will be stopped and started again.
      **/
     void restart();
-    void fallbackToXRenderCompositing();
     void performCompositing();
     void slotConfigChanged();
     void releaseCompositorSelection();

plugins/scenes/opengl/scene_opengl.cpp

@@ -510,7 +510,6 @@ SceneOpenGL *SceneOpenGL::createScene(QObject *parent)
             qCCritical(KWIN_OPENGL) << "OpenGL driver recommends XRender based compositing. Falling back to XRender.";
             qCCritical(KWIN_OPENGL) << "To overwrite the detection use the environment variable KWIN_COMPOSE";
             qCCritical(KWIN_OPENGL) << "For more information see http://community.kde.org/KWin/Environment_Variables#KWIN_COMPOSE";
-            QTimer::singleShot(0, Compositor::self(), SLOT(fallbackToXRenderCompositing()));
         }
         delete backend;
     }