Report partial updates on all outputs

Previously, we couldn't do it because repaints weren't tracked per each
output.

platformsupport/scenes/opengl/backend.cpp

@@ -111,8 +111,9 @@ QSharedPointer<KWin::GLTexture> OpenGLBackend::textureForOutput(AbstractOutput*
     return {};
 }
 
-void OpenGLBackend::aboutToStartPainting(const QRegion &damage)
+void OpenGLBackend::aboutToStartPainting(int screenId, const QRegion &damage)
 {
+    Q_UNUSED(screenId)
     Q_UNUSED(damage)
 }
 

platformsupport/scenes/opengl/backend.h

@@ -70,7 +70,7 @@ public:
      *
      * @p damage contains the reported damage as suggested by windows and effects on prepaint calls.
      */
-    virtual void aboutToStartPainting(const QRegion &damage);
+    virtual void aboutToStartPainting(int screenId, const QRegion &damage);
 
     /**
      * @brief Backend specific code to handle the end of rendering a frame.

plugins/platforms/drm/egl_gbm_backend.cpp

@@ -465,14 +465,10 @@ static QVector<EGLint> regionToRects(const QRegion &region, AbstractWaylandOutpu
     return rects;
 }
 
-void EglGbmBackend::aboutToStartPainting(const QRegion &damagedRegion)
+void EglGbmBackend::aboutToStartPainting(int screenId, const QRegion &damagedRegion)
 {
-    // See EglGbmBackend::endRenderingFrameForScreen comment for the reason why we only support screenId=0
-    if (m_outputs.count() > 1) {
-        return;
-    }
-
-    const Output &output = m_outputs.at(0);
+    Q_ASSERT_X(screenId != -1, "aboutToStartPainting", "not using per screen rendering");
+    const Output &output = m_outputs.at(screenId);
     if (output.bufferAge > 0 && !damagedRegion.isEmpty() && supportsPartialUpdate()) {
         const QRegion region = damagedRegion & output.output->geometry();
 

plugins/platforms/drm/egl_gbm_backend.h

@@ -48,7 +48,7 @@ public:
 protected:
     void present() override;
     void cleanupSurfaces() override;
-    void aboutToStartPainting(const QRegion &damage) override;
+    void aboutToStartPainting(int screenId, const QRegion &damage) override;
 
 private:
     bool initializeEgl();

plugins/platforms/wayland/egl_wayland_backend.cpp

@@ -306,9 +306,10 @@ static QVector<EGLint> regionToRects(const QRegion &region, AbstractWaylandOutpu
     return rects;
 }
 
-void EglWaylandBackend::aboutToStartPainting(const QRegion &damagedRegion)
+void EglWaylandBackend::aboutToStartPainting(int screenId, const QRegion &damagedRegion)
 {
-    EglWaylandOutput* output = m_outputs.at(0);
+    Q_ASSERT_X(screenId != -1, "aboutToStartPainting", "not using per screen rendering");
+    EglWaylandOutput *output = m_outputs.at(screenId);
     if (output->m_bufferAge > 0 && !damagedRegion.isEmpty() && supportsPartialUpdate()) {
         const QRegion region = damagedRegion & output->m_waylandOutput->geometry();
 

plugins/platforms/wayland/egl_wayland_backend.h

@@ -82,7 +82,7 @@ public:
         return m_havePlatformBase;
     }
 
-    void aboutToStartPainting(const QRegion &damage) override;
+    void aboutToStartPainting(int screenId, const QRegion &damage) override;
 
 private:
     bool initializeEgl();

plugins/scenes/opengl/scene_opengl.cpp

@@ -615,9 +615,9 @@ void SceneOpenGL2::paintCursor(const QRegion &rendered)
     glDisable(GL_BLEND);
 }
 
-void SceneOpenGL::aboutToStartPainting(const QRegion &damage)
+void SceneOpenGL::aboutToStartPainting(int screenId, const QRegion &damage)
 {
-    m_backend->aboutToStartPainting(damage);
+    m_backend->aboutToStartPainting(screenId, damage);
 }
 
 qint64 SceneOpenGL::paint(const QRegion &damage, const QList<Toplevel *> &toplevels)

plugins/scenes/opengl/scene_opengl.h

@@ -78,7 +78,7 @@ public:
 protected:
     SceneOpenGL(OpenGLBackend *backend, QObject *parent = nullptr);
     void paintBackground(const QRegion &region) override;
-    void aboutToStartPainting(const QRegion &damage) override;
+    void aboutToStartPainting(int screenId, const QRegion &damage) override;
     void extendPaintRegion(QRegion &region, bool opaqueFullscreen) override;
     QMatrix4x4 transformation(int mask, const ScreenPaintData &data) const;
     void paintDesktop(int desktop, int mask, const QRegion &region, ScreenPaintData &data) override;

scene.cpp

@@ -236,7 +236,7 @@ void Scene::paintGenericScreen(int orig_mask, const ScreenPaintData &)
 
     damaged_region = QRegion(QRect {{}, screens()->size()});
     if (m_paintScreenCount == 1) {
-        aboutToStartPainting(damaged_region);
+        aboutToStartPainting(painted_screen, damaged_region);
 
         if (orig_mask & PAINT_SCREEN_BACKGROUND_FIRST) {
             paintBackground(infiniteRegion());
@@ -377,7 +377,7 @@ void Scene::paintSimpleScreen(int orig_mask, const QRegion &region)
     QRegion paintedArea;
     // Fill any areas of the root window not covered by opaque windows
     if (m_paintScreenCount == 1) {
-        aboutToStartPainting(dirtyArea);
+        aboutToStartPainting(painted_screen, dirtyArea);
 
         if (orig_mask & PAINT_SCREEN_BACKGROUND_FIRST) {
             paintBackground(infiniteRegion());
@@ -636,8 +636,9 @@ void Scene::paintDesktop(int desktop, int mask, const QRegion &region, ScreenPai
     static_cast<EffectsHandlerImpl*>(effects)->paintDesktop(desktop, mask, region, data);
 }
 
-void Scene::aboutToStartPainting(const QRegion &damage)
+void Scene::aboutToStartPainting(int screenId, const QRegion &damage)
 {
+    Q_UNUSED(screenId)
     Q_UNUSED(damage)
 }
 

scene.h

@@ -227,7 +227,7 @@ protected:
      *
      * @p damage contains the reported damage as suggested by windows and effects on prepaint calls.
      */
-    virtual void aboutToStartPainting(const QRegion &damage);
+    virtual void aboutToStartPainting(int screenId, const QRegion &damage);
     // called after all effects had their paintWindow() called
     void finalPaintWindow(EffectWindowImpl* w, int mask, const QRegion &region, WindowPaintData& data);
     // shared implementation, starts painting the window