kwin: Prepare the backend interface for EXT_buffer_age

Allow prepareRenderingFrame() to return a region that will be
repainted in addition to the damaged region.

Pass both the damaged region and the repainted region, which
may be larger, as parameters to endRenderingFrame().

egl_wayland_backend.cpp

@@ -816,17 +816,20 @@ SceneOpenGL::TexturePrivate *EglWaylandBackend::createBackendTexture(SceneOpenGL
     return new EglWaylandTexture(texture, this);
 }
 
-void EglWaylandBackend::prepareRenderingFrame()
+QRegion EglWaylandBackend::prepareRenderingFrame()
 {
     if (!lastDamage().isEmpty())
         present();
+
     eglWaitNative(EGL_CORE_NATIVE_ENGINE);
     startRenderTimer();
+
+    return QRegion();
 }
 
-void EglWaylandBackend::endRenderingFrame(const QRegion &damage)
+void EglWaylandBackend::endRenderingFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
-    setLastDamage(damage);
+    setLastDamage(renderedRegion);
     glFlush();
 }
 

egl_wayland_backend.h

@@ -264,8 +264,8 @@ public:
     virtual ~EglWaylandBackend();
     virtual void screenGeometryChanged(const QSize &size);
     virtual SceneOpenGL::TexturePrivate *createBackendTexture(SceneOpenGL::Texture *texture);
-    virtual void prepareRenderingFrame();
-    virtual void endRenderingFrame(const QRegion &damage);
+    virtual QRegion prepareRenderingFrame();
+    virtual void endRenderingFrame(const QRegion &renderedRegion, const QRegion &damagedRegion);
     Shm *shm();
 
 protected:

eglonxbackend.cpp

@@ -320,7 +320,7 @@ SceneOpenGL::TexturePrivate *EglOnXBackend::createBackendTexture(SceneOpenGL::Te
     return new EglTexture(texture, this);
 }
 
-void EglOnXBackend::prepareRenderingFrame()
+QRegion EglOnXBackend::prepareRenderingFrame()
 {
     if (gs_tripleBufferNeedsDetection) {
         // the composite timer floors the repaint frequency. This can pollute our triple buffering
@@ -330,14 +330,17 @@ void EglOnXBackend::prepareRenderingFrame()
         // fllush the buffer queue
         usleep(1000);
     }
+
     present();
     startRenderTimer();
     eglWaitNative(EGL_CORE_NATIVE_ENGINE);
+
+    return QRegion();
 }
 
-void EglOnXBackend::endRenderingFrame(const QRegion &damage)
+void EglOnXBackend::endRenderingFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
-    setLastDamage(damage);
+    setLastDamage(renderedRegion);
 
     if (!blocksForRetrace()) {
         // This also sets lastDamage to empty which prevents the frame from

eglonxbackend.h

@@ -34,8 +34,8 @@ public:
     virtual ~EglOnXBackend();
     virtual void screenGeometryChanged(const QSize &size);
     virtual SceneOpenGL::TexturePrivate *createBackendTexture(SceneOpenGL::Texture *texture);
-    virtual void prepareRenderingFrame();
-    virtual void endRenderingFrame(const QRegion &damage);
+    virtual QRegion prepareRenderingFrame();
+    virtual void endRenderingFrame(const QRegion &renderedRegion, const QRegion &damagedRegion);
 
 protected:
     virtual void present();

glxbackend.cpp

@@ -493,7 +493,7 @@ SceneOpenGL::TexturePrivate *GlxBackend::createBackendTexture(SceneOpenGL::Textu
     return new GlxTexture(texture, this);
 }
 
-void GlxBackend::prepareRenderingFrame()
+QRegion GlxBackend::prepareRenderingFrame()
 {
     if (gs_tripleBufferNeedsDetection) {
         // the composite timer floors the repaint frequency. This can pollute our triple buffering
@@ -506,11 +506,13 @@ void GlxBackend::prepareRenderingFrame()
     present();
     startRenderTimer();
     glXWaitX();
+
+    return QRegion();
 }
 
-void GlxBackend::endRenderingFrame(const QRegion &damage)
+void GlxBackend::endRenderingFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
-    setLastDamage(damage);
+    setLastDamage(renderedRegion);
 
     if (!blocksForRetrace()) {
         // This also sets lastDamage to empty which prevents the frame from

glxbackend.h

@@ -44,8 +44,8 @@ public:
     virtual ~GlxBackend();
     virtual void screenGeometryChanged(const QSize &size);
     virtual SceneOpenGL::TexturePrivate *createBackendTexture(SceneOpenGL::Texture *texture);
-    virtual void prepareRenderingFrame();
-    virtual void endRenderingFrame(const QRegion &damage);
+    virtual QRegion prepareRenderingFrame();
+    virtual void endRenderingFrame(const QRegion &renderedRegion, const QRegion &damagedRegion);
 
 protected:
     virtual void present();

scene_opengl.cpp

@@ -372,7 +372,7 @@ qint64 SceneOpenGL::paint(QRegion damage, ToplevelList toplevels)
     checkGLError("Paint2");
 #endif
 
-    m_backend->endRenderingFrame(damage);
+    m_backend->endRenderingFrame(damage, damage);
 
     // do cleanup
     stacking_order.clear();

scene_opengl.h

@@ -461,21 +461,28 @@ public:
     }
     virtual void screenGeometryChanged(const QSize &size) = 0;
     virtual SceneOpenGL::TexturePrivate *createBackendTexture(SceneOpenGL::Texture *texture) = 0;
+
     /**
      * @brief Backend specific code to prepare the rendering of a frame including flushing the
      * previously rendered frame to the screen if the backend works this way.
+     *
+     * @return A region that if not empty will be repainted in addition to the damaged region
      **/
-    virtual void prepareRenderingFrame() = 0;
+    virtual QRegion prepareRenderingFrame() = 0;
+
     /**
      * @brief Backend specific code to handle the end of rendering a frame.
      *
-     * @param damage The actual updated region in this frame
+     * @param renderedRegion The possibly larger region that has been rendered
+     * @param damagedRegion The damaged region that should be posted
      **/
-    virtual void endRenderingFrame(const QRegion &damage) = 0;
+    virtual void endRenderingFrame(const QRegion &renderedRegion, const QRegion &damagedRegion) = 0;
+
     /**
      * @brief Compositor is going into idle mode, flushes any pending paints.
      **/
     void idle();
+
     /**
      * @return bool Whether the scene needs to flush a frame.
      **/