The actual patch - tearing-fix.patch

tearing-fix.patch (text/plain), 23.55 KB, created by Mike Lothian on 2013-03-14 19:00:14 UTC

commit 6072b4feb8c90024aa24b2e9cb8a21ab2140412c
Author: Thomas Lübking <[e-mail]>
Date:   Mon Feb 18 23:17:46 2013 +0100

    support a permanent glSwapBuffer
    
    either by
    - forcing fullrepaints unconditionally
    - turning a repaint to a full one beyond a threshhold
    - completing the the backbuffer from the frontbuffer after the paint
    
    BUG: 307965
    FIXED-IN: 4.10
    REVIEW: 107198

diff --git a/kwin/composite.cpp b/kwin/composite.cpp
index 5702ec0..1e77b5c 100644
--- a/kwin/composite.cpp
+++ b/kwin/composite.cpp
@@ -501,8 +501,6 @@ void Compositor::timerEvent(QTimerEvent *te)
         QObject::timerEvent(te);
 }
 
-static int s_pendingFlushes = 0;
-
 void Compositor::performCompositing()
 {
     if (!isOverlayWindowVisible())
@@ -543,15 +541,7 @@ void Compositor::performCompositing()
         win->getDamageRegionReply();
     }
 
-    bool pending = !repaints_region.isEmpty() || windowRepaintsPending();
-    if (pending)
-        s_pendingFlushes = 3;
-    else if (m_scene->hasPendingFlush())
-        --s_pendingFlushes;
-    else
-        s_pendingFlushes = 0;
-    if (s_pendingFlushes < 1) {
-        s_pendingFlushes = 0;
+    if (repaints_region.isEmpty() && !windowRepaintsPending()) {
         m_scene->idle();
         // Note: It would seem here we should undo suspended unredirect, but when scenes need
         // it for some reason, e.g. transformations or translucency, the next pass that does not
diff --git a/kwin/eglonxbackend.cpp b/kwin/eglonxbackend.cpp
index dcb70d8..a34685a 100644
--- a/kwin/eglonxbackend.cpp
+++ b/kwin/eglonxbackend.cpp
@@ -194,12 +194,13 @@ bool EglOnXBackend::initBufferConfigs()
 
 void EglOnXBackend::present()
 {
-    if (lastMask() & Scene::PAINT_SCREEN_REGION && surfaceHasSubPost && eglPostSubBufferNV) {
+    const bool swap = (options->glPreferBufferSwap() && options->glPreferBufferSwap() != Options::ExtendDamage) ||
+                      !(lastMask() & Scene::PAINT_SCREEN_REGION && surfaceHasSubPost && eglPostSubBufferNV);
+    if (swap) {
+        eglSwapBuffers(dpy, surface);
+    } else {
         const QRect damageRect = lastDamage().boundingRect();
-
         eglPostSubBufferNV(dpy, surface, damageRect.left(), displayHeight() - damageRect.bottom() - 1, damageRect.width(), damageRect.height());
-    } else {
-        eglSwapBuffers(dpy, surface);
     }
 
     eglWaitGL();
diff --git a/kwin/glxbackend.cpp b/kwin/glxbackend.cpp
index be11497..17d01e7 100644
--- a/kwin/glxbackend.cpp
+++ b/kwin/glxbackend.cpp
@@ -115,7 +115,7 @@ void GlxBackend::init()
                     // However mesa/dri will return a range error (6) because deactivating the
                     // swapinterval (as of today) seems completely unsupported
                     setHasWaitSync(true);
-                    setSwapInterval(0);
+                    setSwapInterval(1);
                 }
                 else
                     qWarning() << "NO VSYNC! glXWaitVideoSync(1,0,&uint) isn't 0 but" << glXWaitVideoSync(1, 0, &sync);
@@ -473,77 +473,80 @@ void GlxBackend::waitSync()
 
 void GlxBackend::present()
 {
+    QRegion displayRegion(0, 0, displayWidth(), displayHeight());
+    const bool fullRepaint = (lastDamage() == displayRegion);
+
     if (isDoubleBuffer()) {
-        if (lastMask() & Scene::PAINT_SCREEN_REGION) {
-            waitSync();
-            if (glXCopySubBuffer) {
-                foreach (const QRect & r, lastDamage().rects()) {
-                    // convert to OpenGL coordinates
-                    int y = displayHeight() - r.y() - r.height();
-                    glXCopySubBuffer(display(), glxbuffer, r.x(), y, r.width(), r.height());
-                }
-            } else {
-                // if a shader is bound or the texture unit is enabled, copy pixels results in a black screen
-                // therefore unbind the shader and restore after copying the pixels
-                GLint shader = 0;
-                if (ShaderManager::instance()->isShaderBound()) {
-                    glGetIntegerv(GL_CURRENT_PROGRAM, &shader);
-                    glUseProgram(0);
-                }
-                bool reenableTexUnit = false;
-                if (glIsEnabled(GL_TEXTURE_2D)) {
-                    glDisable(GL_TEXTURE_2D);
-                    reenableTexUnit = true;
-                }
-                // no idea why glScissor() is used, but Compiz has it and it doesn't seem to hurt
-                glEnable(GL_SCISSOR_TEST);
-                glDrawBuffer(GL_FRONT);
-                int xpos = 0;
-                int ypos = 0;
-                foreach (const QRect & r, lastDamage().rects()) {
-                    // convert to OpenGL coordinates
-                    int y = displayHeight() - r.y() - r.height();
-                    // Move raster position relatively using glBitmap() rather
-                    // than using glRasterPos2f() - the latter causes drawing
-                    // artefacts at the bottom screen edge with some gfx cards
-//                    glRasterPos2f( r.x(), r.y() + r.height());
-                    glBitmap(0, 0, 0, 0, r.x() - xpos, y - ypos, NULL);
-                    xpos = r.x();
-                    ypos = y;
-                    glScissor(r.x(), y, r.width(), r.height());
-                    glCopyPixels(r.x(), y, r.width(), r.height(), GL_COLOR);
-                }
-                glBitmap(0, 0, 0, 0, -xpos, -ypos, NULL);   // move position back to 0,0
-                glDrawBuffer(GL_BACK);
-                glDisable(GL_SCISSOR_TEST);
-                if (reenableTexUnit) {
-                    glEnable(GL_TEXTURE_2D);
-                }
-                // rebind previously bound shader
-                if (ShaderManager::instance()->isShaderBound()) {
-                    glUseProgram(shader);
-                }
-            }
-        } else {
+
+        if (fullRepaint) {
             if (haveSwapInterval) {
-                setSwapInterval(options->isGlVSync() ? 1 : 0);
                 glXSwapBuffers(display(), glxbuffer);
-                setSwapInterval(0);
-                startRenderTimer(); // this is important so we don't assume to be loosing frames in the compositor timing calculation
+                startRenderTimer();
             } else {
-                waitSync();
+                waitSync(); // calls startRenderTimer();
                 glXSwapBuffers(display(), glxbuffer);
             }
+        } else if (glXCopySubBuffer) {
+            waitSync();
+            foreach (const QRect & r, lastDamage().rects()) {
+                // convert to OpenGL coordinates
+                int y = displayHeight() - r.y() - r.height();
+                glXCopySubBuffer(display(), glxbuffer, r.x(), y, r.width(), r.height());
+            }
+        } else { // Copy Pixels
+            // if a shader is bound or the texture unit is enabled, copy pixels results in a black screen
+            // therefore unbind the shader and restore after copying the pixels
+            GLint shader = 0;
+            if (ShaderManager::instance()->isShaderBound()) {
+                glGetIntegerv(GL_CURRENT_PROGRAM, &shader);
+                glUseProgram(0);
+            }
+            bool reenableTexUnit = false;
+            if (glIsEnabled(GL_TEXTURE_2D)) {
+                glDisable(GL_TEXTURE_2D);
+                reenableTexUnit = true;
+            }
+            // no idea why glScissor() is used, but Compiz has it and it doesn't seem to hurt
+            glEnable(GL_SCISSOR_TEST);
+            glDrawBuffer(GL_FRONT);
+            waitSync();
+            int xpos = 0;
+            int ypos = 0;
+            foreach (const QRect & r, lastDamage().rects()) {
+                // convert to OpenGL coordinates
+                int y = displayHeight() - r.y() - r.height();
+                // Move raster position relatively using glBitmap() rather
+                // than using glRasterPos2f() - the latter causes drawing
+                // artefacts at the bottom screen edge with some gfx cards
+//                    glRasterPos2f( r.x(), r.y() + r.height());
+                glBitmap(0, 0, 0, 0, r.x() - xpos, y - ypos, NULL);
+                xpos = r.x();
+                ypos = y;
+                glScissor(r.x(), y, r.width(), r.height());
+                glCopyPixels(r.x(), y, r.width(), r.height(), GL_COLOR);
+            }
+            glBitmap(0, 0, 0, 0, -xpos, -ypos, NULL);   // move position back to 0,0
+            glDrawBuffer(GL_BACK);
+            glDisable(GL_SCISSOR_TEST);
+            if (reenableTexUnit) {
+                glEnable(GL_TEXTURE_2D);
+            }
+            // rebind previously bound shader
+            if (ShaderManager::instance()->isShaderBound()) {
+                glUseProgram(shader);
+            }
         }
+
         glXWaitGL();
     } else {
         glXWaitGL();
-        if (lastMask() & Scene::PAINT_SCREEN_REGION)
+        if (!fullRepaint)
             foreach (const QRect & r, lastDamage().rects())
                 XCopyArea(display(), buffer, rootWindow(), gcroot, r.x(), r.y(), r.width(), r.height(), r.x(), r.y());
         else
             XCopyArea(display(), buffer, rootWindow(), gcroot, 0, 0, displayWidth(), displayHeight(), 0, 0);
     }
+    setLastDamage(QRegion());
     XFlush(display());
 }
 
diff --git a/kwin/options.cpp b/kwin/options.cpp
index c0150a2..46a9396 100644
--- a/kwin/options.cpp
+++ b/kwin/options.cpp
@@ -161,6 +161,7 @@ Options::Options(QObject *parent)
     , m_glStrictBinding(Options::defaultGlStrictBinding())
     , m_glStrictBindingFollowsDriver(Options::defaultGlStrictBindingFollowsDriver())
     , m_glLegacy(Options::defaultGlLegacy())
+    , m_glPreferBufferSwap(Options::defaultGlPreferBufferSwap())
     , OpTitlebarDblClick(Options::defaultOperationTitlebarDblClick())
     , CmdActiveTitlebar1(Options::defaultCommandActiveTitlebar1())
     , CmdActiveTitlebar2(Options::defaultCommandActiveTitlebar2())
@@ -768,6 +769,24 @@ void Options::setGlLegacy(bool glLegacy)
     emit glLegacyChanged();
 }
 
+void Options::setGlPreferBufferSwap(char glPreferBufferSwap)
+{
+    if (glPreferBufferSwap == 'a') {
+        // buffer cpying is very fast with the nvidia blob
+        // but due to restrictions in DRI2 *incredibly* slow for all MESA drivers
+        // see http://www.x.org/releases/X11R7.7/doc/dri2proto/dri2proto.txt, item 2.5
+        if (GLPlatform::instance()->driver() == Driver_NVidia)
+            glPreferBufferSwap = CopyFrontBuffer;
+        else
+            glPreferBufferSwap = ExtendDamage;
+    }
+    if (m_glPreferBufferSwap == (GlSwapStrategy)glPreferBufferSwap) {
+        return;
+    }
+    m_glPreferBufferSwap = (GlSwapStrategy)glPreferBufferSwap;
+    emit glPreferBufferSwapChanged();
+}
+
 void Options::reparseConfiguration()
 {
     KGlobal::config()->reparseConfiguration();
@@ -957,6 +976,16 @@ void Options::reloadCompositingSettings(bool force)
     }
     setGlLegacy(config.readEntry("GLLegacy", Options::defaultGlLegacy()));
 
+    char c = 0;
+    if (isGlVSync()) { // buffer swap enforcement makes little sense without
+        const QString s = config.readEntry("GLPreferBufferSwap", QString(Options::defaultGlPreferBufferSwap()));
+        if (!s.isEmpty())
+            c = s.at(0).toAscii();
+        if (c != 'a' && c != 'c' && c != 'p' && c != 'e')
+            c = 0;
+    }
+    setGlPreferBufferSwap(c);
+
     setColorCorrected(config.readEntry("GLColorCorrection", Options::defaultColorCorrected()));
 
     m_xrenderSmoothScale = config.readEntry("XRenderSmoothScale", false);
diff --git a/kwin/options.h b/kwin/options.h
index c76dbae..e816d4a 100644
--- a/kwin/options.h
+++ b/kwin/options.h
@@ -42,6 +42,7 @@ class Options : public QObject, public KDecorationOptions
 {
     Q_OBJECT
     Q_ENUMS(FocusPolicy)
+    Q_ENUMS(GlSwapStrategy)
     Q_ENUMS(MouseCommand)
     Q_ENUMS(MouseWheelCommand)
 
@@ -187,6 +188,7 @@ class Options : public QObject, public KDecorationOptions
      * Whether legacy OpenGL should be used or OpenGL (ES) 2
      **/
     Q_PROPERTY(bool glLegacy READ isGlLegacy WRITE setGlLegacy NOTIFY glLegacyChanged)
+    Q_PROPERTY(char glPreferBufferSwap READ glPreferBufferSwap WRITE setGlPreferBufferSwap NOTIFY glPreferBufferSwapChanged)
 public:
 
     explicit Options(QObject *parent = NULL);
@@ -549,6 +551,11 @@ public:
         return m_glLegacy;
     }
 
+    enum GlSwapStrategy { NoSwapEncourage = 0, CopyFrontBuffer = 'c', PaintFullScreen = 'p', ExtendDamage = 'e', AutoSwapStrategy = 'a' };
+    GlSwapStrategy glPreferBufferSwap() const {
+        return m_glPreferBufferSwap;
+    }
+
     // setters
     void setFocusPolicy(FocusPolicy focusPolicy);
     void setNextFocusPrefersMouse(bool nextFocusPrefersMouse);
@@ -610,6 +617,7 @@ public:
     void setGlStrictBinding(bool glStrictBinding);
     void setGlStrictBindingFollowsDriver(bool glStrictBindingFollowsDriver);
     void setGlLegacy(bool glLegacy);
+    void setGlPreferBufferSwap(char glPreferBufferSwap);
 
     // default values
     static WindowOperation defaultOperationTitlebarDblClick() {
@@ -717,6 +725,9 @@ public:
     static bool defaultGlLegacy() {
         return false;
     }
+    static GlSwapStrategy defaultGlPreferBufferSwap() {
+        return AutoSwapStrategy;
+    }
     static int defaultAnimationSpeed() {
         return 3;
     }
@@ -797,6 +808,7 @@ Q_SIGNALS:
     void glStrictBindingChanged();
     void glStrictBindingFollowsDriverChanged();
     void glLegacyChanged();
+    void glPreferBufferSwapChanged();
 
 public Q_SLOTS:
     void setColorCorrected(bool colorCorrected = false);
@@ -847,6 +859,7 @@ private:
     bool m_glStrictBinding;
     bool m_glStrictBindingFollowsDriver;
     bool m_glLegacy;
+    GlSwapStrategy m_glPreferBufferSwap;
 
     WindowOperation OpTitlebarDblClick;
 
diff --git a/kwin/scene.cpp b/kwin/scene.cpp
index 685254b..939f000 100644
--- a/kwin/scene.cpp
+++ b/kwin/scene.cpp
@@ -103,8 +103,9 @@ Scene::~Scene()
 // returns mask and possibly modified region
 void Scene::paintScreen(int* mask, QRegion* region)
 {
-    *mask = (*region == QRegion(0, 0, displayWidth(), displayHeight()))
-            ? 0 : PAINT_SCREEN_REGION;
+    const QRegion displayRegion(0, 0, displayWidth(), displayHeight());
+    *mask = (*region == displayRegion) ? 0 : PAINT_SCREEN_REGION;
+
     updateTimeDiff();
     // preparation step
     static_cast<EffectsHandlerImpl*>(effects)->startPaint();
@@ -124,10 +125,10 @@ void Scene::paintScreen(int* mask, QRegion* region)
         *region = infiniteRegion();
     } else if (*mask & PAINT_SCREEN_REGION) {
         // make sure not to go outside visible screen
-        *region &= QRegion(0, 0, displayWidth(), displayHeight());
+        *region &= displayRegion;
     } else {
         // whole screen, not transformed, force region to be full
-        *region = QRegion(0, 0, displayWidth(), displayHeight());
+        *region = displayRegion;
     }
     painted_region = *region;
     if (*mask & PAINT_SCREEN_BACKGROUND_FIRST) {
@@ -141,7 +142,7 @@ void Scene::paintScreen(int* mask, QRegion* region)
     effects->postPaintScreen();
     *region |= painted_region;
     // make sure not to go outside of the screen area
-    *region &= QRegion(0, 0, displayWidth(), displayHeight());
+    *region &= displayRegion;
     // make sure all clipping is restored
     Q_ASSERT(!PaintClipper::clip());
 }
@@ -236,6 +237,7 @@ void Scene::paintSimpleScreen(int orig_mask, QRegion region)
     QList< QPair< Window*, Phase2Data > > phase2data;
 
     QRegion dirtyArea = region;
+    bool opaqueFullscreen(false);
     for (int i = 0;  // do prePaintWindow bottom to top
             i < stacking_order.count();
             ++i) {
@@ -254,10 +256,12 @@ void Scene::paintSimpleScreen(int orig_mask, QRegion region)
         topw->resetRepaints();
 
         // Clip out the decoration for opaque windows; the decoration is drawn in the second pass
+        opaqueFullscreen = false; // TODO: do we care about unmanged windows here (maybe input windows?)
         if (w->isOpaque()) {
             Client *c = NULL;
             if (topw->isClient()) {
                 c = static_cast<Client*>(topw);
+                opaqueFullscreen = c->isFullScreen();
             }
             // the window is fully opaque
             if (c && c->decorationHasAlpha()) {
@@ -297,13 +301,24 @@ void Scene::paintSimpleScreen(int orig_mask, QRegion region)
         w->suspendUnredirect(data.mask & PAINT_WINDOW_TRANSLUCENT);
     }
 
-    // This is the occlusion culling pass
+    const QRegion displayRegion(0, 0, displayWidth(), displayHeight());
+
+    bool fullRepaint(dirtyArea == displayRegion); // spare some expensive region operations
+    if (!fullRepaint) {
+        extendPaintRegion(dirtyArea, opaqueFullscreen);
+        fullRepaint = (dirtyArea == displayRegion);
+    }
+
     QRegion allclips, upperTranslucentDamage;
+    // This is the occlusion culling pass
     for (int i = phase2data.count() - 1; i >= 0; --i) {
         QPair< Window*, Phase2Data > *entry = &phase2data[i];
         Phase2Data *data = &entry->second;
 
-        data->region |= upperTranslucentDamage;
+        if (fullRepaint)
+            data->region = displayRegion;
+        else
+            data->region |= upperTranslucentDamage;
 
         // subtract the parts which will possibly been drawn as part of
         // a higher opaque window
@@ -315,8 +330,9 @@ void Scene::paintSimpleScreen(int orig_mask, QRegion region)
             // clip away the opaque regions for all windows below this one
             allclips |= data->clip;
             // extend the translucent damage for windows below this by remaining (translucent) regions
-            upperTranslucentDamage |= data->region - data->clip;
-        } else {
+            if (!fullRepaint)
+                upperTranslucentDamage |= data->region - data->clip;
+        } else if (!fullRepaint) {
             upperTranslucentDamage |= data->region;
         }
     }
@@ -338,7 +354,10 @@ void Scene::paintSimpleScreen(int orig_mask, QRegion region)
 
         paintWindow(data->window, data->mask, data->region, data->quads);
     }
-    painted_region |= paintedArea;
+    if (fullRepaint)
+        painted_region = displayRegion;
+    else
+        painted_region |= paintedArea;
 }
 
 void Scene::paintWindow(Window* w, int mask, QRegion region, WindowQuadList quads)
@@ -452,6 +471,12 @@ void Scene::finalDrawWindow(EffectWindowImpl* w, int mask, QRegion region, Windo
     w->sceneWindow()->performPaint(mask, region, data);
 }
 
+void Scene::extendPaintRegion(QRegion &region, bool opaqueFullscreen)
+{
+    Q_UNUSED(region);
+    Q_UNUSED(opaqueFullscreen);
+}
+
 bool Scene::waitSyncAvailable() const
 {
     return false;
diff --git a/kwin/scene.h b/kwin/scene.h
index f06d150..5d49c40 100644
--- a/kwin/scene.h
+++ b/kwin/scene.h
@@ -125,6 +125,9 @@ protected:
     virtual void paintWindow(Window* w, int mask, QRegion region, WindowQuadList quads);
     // called after all effects had their drawWindow() called
     virtual void finalDrawWindow(EffectWindowImpl* w, int mask, QRegion region, WindowPaintData& data);
+    // let the scene decide whether it's better to paint more of the screen, eg. in order to allow a buffer swap
+    // the default is NOOP
+    virtual void extendPaintRegion(QRegion &region, bool opaqueFullscreen);
     // compute time since the last repaint
     void updateTimeDiff();
     // saved data for 2nd pass of optimized screen painting
diff --git a/kwin/scene_opengl.cpp b/kwin/scene_opengl.cpp
index 3185c9e..a9c5d84 100644
--- a/kwin/scene_opengl.cpp
+++ b/kwin/scene_opengl.cpp
@@ -98,7 +98,8 @@ void OpenGLBackend::setFailed(const QString &reason)
 
 void OpenGLBackend::idle()
 {
-    present();
+    if (hasPendingFlush())
+        present();
 }
 
 /************************************************
@@ -269,7 +270,52 @@ int SceneOpenGL::paint(QRegion damage, ToplevelList toplevels)
 #ifdef CHECK_GL_ERROR
     checkGLError("Paint1");
 #endif
+
+    const QRegion displayRegion(0, 0, displayWidth(), displayHeight());
     paintScreen(&mask, &damage);   // call generic implementation
+#ifndef KWIN_HAVE_OPENGLES
+    // copy dirty parts from front to backbuffer
+    if (options->glPreferBufferSwap() == Options::CopyFrontBuffer && damage != displayRegion) {
+        GLint shader = 0;
+        if (ShaderManager::instance()->isShaderBound()) {
+            glGetIntegerv(GL_CURRENT_PROGRAM, &shader);
+            glUseProgram(0);
+        }
+        bool reenableTexUnit = false;
+        if (glIsEnabled(GL_TEXTURE_2D)) {
+            glDisable(GL_TEXTURE_2D);
+            reenableTexUnit = true;
+        }
+        // no idea why glScissor() is used, but Compiz has it and it doesn't seem to hurt
+        glEnable(GL_SCISSOR_TEST);
+        glReadBuffer(GL_FRONT);
+
+        int xpos = 0;
+        int ypos = 0;
+        const QRegion dirty = displayRegion - damage;
+        foreach (const QRect &r, dirty.rects()) {
+            // convert to OpenGL coordinates
+            int y = displayHeight() - r.y() - r.height();
+            glBitmap(0, 0, 0, 0, r.x() - xpos, y - ypos, NULL); // not glRasterPos2f, see glxbackend.cpp
+            xpos = r.x();
+            ypos = y;
+            glScissor(r.x(), y, r.width(), r.height());
+            glCopyPixels(r.x(), y, r.width(), r.height(), GL_COLOR);
+        }
+
+        glBitmap(0, 0, 0, 0, -xpos, -ypos, NULL); // move position back to 0,0
+        glReadBuffer(GL_BACK);
+        glDisable(GL_SCISSOR_TEST);
+        if (reenableTexUnit) {
+            glEnable(GL_TEXTURE_2D);
+        }
+        // rebind previously bound shader
+        if (ShaderManager::instance()->isShaderBound()) {
+            glUseProgram(shader);
+        }
+        damage = displayRegion;
+    }
+#endif
 #ifdef CHECK_GL_ERROR
     checkGLError("Paint2");
 #endif
@@ -328,6 +374,35 @@ void SceneOpenGL::paintBackground(QRegion region)
     doPaintBackground(verts);
 }
 
+void SceneOpenGL::extendPaintRegion(QRegion &region, bool opaqueFullscreen)
+{
+#ifndef KWIN_HAVE_OPENGLES
+    if (options->glPreferBufferSwap() == Options::ExtendDamage) { // only Extend "large" repaints
+        const QRegion displayRegion(0, 0, displayWidth(), displayHeight());
+        uint damagedPixels = 0;
+        const uint fullRepaintLimit = (opaqueFullscreen?0.49f:0.748f)*displayWidth()*displayHeight();
+        // 16:9 is 75% of 4:3 and 2.55:1 is 49.01% of 5:4
+        // (5:4 is the most square format and 2.55:1 is Cinemascope55 - the widest ever shot
+        // movie aspect - two times ;-) It's a Fox format, though, so maybe we want to restrict
+        // to 2.20:1 - Panavision - which has actually been used for interesting movies ...)
+        // would be 57% of 5/4
+        foreach (const QRect &r, region.rects()) {
+//                 damagedPixels += r.width() * r.height(); // combined window damage test
+            damagedPixels = r.width() * r.height(); // experimental single window damage testing
+            if (damagedPixels > fullRepaintLimit) {
+                region = displayRegion;
+                return;
+            }
+        }
+    } else if (options->glPreferBufferSwap() == Options::PaintFullScreen) { // forced full rePaint
+        region = QRegion(0, 0, displayWidth(), displayHeight());
+    }
+#else
+    Q_UNUSED(region);
+    Q_UNUSED(opaqueFullscreen);
+#endif
+}
+
 void SceneOpenGL::windowAdded(Toplevel* c)
 {
     assert(!windows.contains(c));
diff --git a/kwin/scene_opengl.h b/kwin/scene_opengl.h
index 7971c83..cd3dd86 100644
--- a/kwin/scene_opengl.h
+++ b/kwin/scene_opengl.h
@@ -68,6 +68,7 @@ public:
 protected:
     SceneOpenGL(Workspace* ws, OpenGLBackend *backend);
     virtual void paintBackground(QRegion region);
+    virtual void extendPaintRegion(QRegion &region, bool opaqueFullscreen);
     QMatrix4x4 transformation(int mask, const ScreenPaintData &data) const;
 
     virtual void doPaintBackground(const QVector<float> &vertices) = 0;