wayland: Schedule repaints even on empty commits

If only frame callbacks have been committed, the compositor must still
schedule compositing.

BUG: 428499

scene.cpp

@@ -778,6 +778,13 @@ Scene::Window::Window(Toplevel *client, QObject *parent)
                 this, &Window::discardPixmap);
         connect(surface, &KWaylandServer::SurfaceInterface::surfaceToBufferMatrixChanged,
                 this, &Window::discardQuads);
+
+        connect(m_subsurfaceMonitor, &SubSurfaceMonitor::subSurfaceCommitted, this, [this](KWaylandServer::SubSurfaceInterface *subsurface) {
+            handleSurfaceCommitted(subsurface->surface());
+        });
+        connect(surface, &KWaylandServer::SurfaceInterface::committed, this, [this, surface]() {
+            handleSurfaceCommitted(surface);
+        });
     }
 
     connect(toplevel, &Toplevel::screenScaleChanged, this, &Window::discardQuads);
@@ -1218,6 +1225,27 @@ void Scene::Window::reallocRepaints()
     m_repaints.fill(infiniteRegion());
 }
 
+void Scene::Window::scheduleRepaint()
+{
+    if (kwinApp()->platform()->isPerScreenRenderingEnabled()) {
+        const QVector<AbstractOutput *> outputs = kwinApp()->platform()->enabledOutputs();
+        for (AbstractOutput *output : outputs) {
+            if (window()->isOnOutput(output)) {
+                output->renderLoop()->scheduleRepaint();
+            }
+        }
+    } else {
+        kwinApp()->platform()->renderLoop()->scheduleRepaint();
+    }
+}
+
+void Scene::Window::handleSurfaceCommitted(KWaylandServer::SurfaceInterface *surface)
+{
+    if (surface->hasFrameCallbacks()) {
+        scheduleRepaint();
+    }
+}
+
 //****************************************
 // WindowPixmap
 //****************************************

scene.h

@@ -400,6 +400,8 @@ protected:
     ImageFilterType filter;
     Shadow *m_shadow;
 private:
+    void scheduleRepaint();
+    void handleSurfaceCommitted(KWaylandServer::SurfaceInterface *surface);
     void reallocRepaints();
 
     QScopedPointer<WindowPixmap> m_currentPixmap;

subsurfacemonitor.cpp

@@ -39,6 +39,8 @@ void SubSurfaceMonitor::registerSubSurface(SubSurfaceInterface *subSurface)
             this, &SubSurfaceMonitor::subSurfaceSurfaceToBufferMatrixChanged);
     connect(surface, &SurfaceInterface::bufferSizeChanged,
             this, &SubSurfaceMonitor::subSurfaceBufferSizeChanged);
+    connect(surface, &SurfaceInterface::committed,
+            this, [this, subSurface]() { emit subSurfaceCommitted(subSurface); });
 
     registerSurface(surface);
 }
@@ -49,18 +51,7 @@ void SubSurfaceMonitor::unregisterSubSurface(SubSurfaceInterface *subSurface)
     if (!surface)
         return;
 
-    disconnect(subSurface, &SubSurfaceInterface::positionChanged,
-               this, &SubSurfaceMonitor::subSurfaceMoved);
-    disconnect(surface, &SurfaceInterface::sizeChanged,
-               this, &SubSurfaceMonitor::subSurfaceResized);
-    disconnect(surface, &SurfaceInterface::mapped,
-               this, &SubSurfaceMonitor::subSurfaceMapped);
-    disconnect(surface, &SurfaceInterface::unmapped,
-               this, &SubSurfaceMonitor::subSurfaceUnmapped);
-    disconnect(surface, &SurfaceInterface::surfaceToBufferMatrixChanged,
-               this, &SubSurfaceMonitor::subSurfaceSurfaceToBufferMatrixChanged);
-    disconnect(surface, &SurfaceInterface::bufferSizeChanged,
-               this, &SubSurfaceMonitor::subSurfaceBufferSizeChanged);
+    disconnect(subSurface, nullptr, this, nullptr);
 
     unregisterSurface(surface);
 }
@@ -79,14 +70,7 @@ void SubSurfaceMonitor::registerSurface(SurfaceInterface *surface)
 
 void SubSurfaceMonitor::unregisterSurface(SurfaceInterface *surface)
 {
-    disconnect(surface, &SurfaceInterface::childSubSurfaceAdded,
-               this, &SubSurfaceMonitor::subSurfaceAdded);
-    disconnect(surface, &SurfaceInterface::childSubSurfaceRemoved,
-               this, &SubSurfaceMonitor::subSurfaceRemoved);
-    disconnect(surface, &SurfaceInterface::childSubSurfaceAdded,
-               this, &SubSurfaceMonitor::registerSubSurface);
-    disconnect(surface, &SurfaceInterface::childSubSurfaceRemoved,
-               this, &SubSurfaceMonitor::unregisterSubSurface);
+    disconnect(surface, nullptr, this, nullptr);
 }
 
 } // namespace KWin

subsurfacemonitor.h

@@ -68,6 +68,7 @@ Q_SIGNALS:
      * This signal is emitted when the buffer size of a subsurface has changed.
      */
     void subSurfaceBufferSizeChanged();
+    void subSurfaceCommitted(KWaylandServer::SubSurfaceInterface *subSurface);
 
 private:
     void registerSubSurface(KWaylandServer::SubSurfaceInterface *subSurface);

toplevel.cpp

@@ -9,6 +9,7 @@
 #include "toplevel.h"
 
 #include "abstract_client.h"
+#include "abstract_output.h"
 #ifdef KWIN_BUILD_ACTIVITIES
 #include "activities.h"
 #endif
@@ -563,6 +564,11 @@ bool Toplevel::isOnActiveScreen() const
     return isOnScreen(screens()->current());
 }
 
+bool Toplevel::isOnOutput(AbstractOutput *output) const
+{
+    return output->geometry().intersects(frameGeometry());
+}
+
 void Toplevel::updateShadow()
 {
     QRect dirtyRect;  // old & new shadow region

toplevel.h

@@ -37,6 +37,7 @@ class SurfaceInterface;
 namespace KWin
 {
 
+class AbstractOutput;
 class ClientMachine;
 class Deleted;
 class EffectWindowImpl;
@@ -347,6 +348,7 @@ public:
     int width() const;
     int height() const;
     bool isOnScreen(int screen) const;   // true if it's at least partially there
+    bool isOnOutput(AbstractOutput *output) const;
     bool isOnActiveScreen() const;
     int screen() const; // the screen where the center is
     /**