RenderLoop: restrict repaint scheduling with fullscreen windows

With an opaque fullscreen window we can be sure that items under it don't
actually require us to repaint. This should yield some small efficiency
improvements and resolves stutter with adaptive sync.

BUG: 443872
FIXED-IN: 5.23.3

src/item.cpp

@@ -261,12 +261,12 @@ void Item::scheduleRepaintInternal(const QRegion &region)
             const QRegion dirtyRegion = globalRegion & output->geometry();
             if (!dirtyRegion.isEmpty()) {
                 m_repaints[output] += dirtyRegion;
-                output->renderLoop()->scheduleRepaint();
+                output->renderLoop()->scheduleRepaint(this);
             }
         }
     } else {
         m_repaints[nullptr] += globalRegion;
-        kwinApp()->platform()->renderLoop()->scheduleRepaint();
+        kwinApp()->platform()->renderLoop()->scheduleRepaint(this);
     }
 }
 
@@ -280,11 +280,11 @@ void Item::scheduleFrame()
         const QVector<AbstractOutput *> outputs = kwinApp()->platform()->enabledOutputs();
         for (const AbstractOutput *output : outputs) {
             if (output->geometry().intersects(geometry)) {
-                output->renderLoop()->scheduleRepaint();
+                output->renderLoop()->scheduleRepaint(this);
             }
         }
     } else {
-        kwinApp()->platform()->renderLoop()->scheduleRepaint();
+        kwinApp()->platform()->renderLoop()->scheduleRepaint(this);
     }
 }
 

src/renderloop.cpp

@@ -36,7 +36,7 @@ void RenderLoopPrivate::scheduleRepaint()
     if (kwinApp()->isTerminating() || compositeTimer.isActive()) {
         return;
     }
-    if (vrrPolicy == RenderLoop::VrrPolicy::Always || (vrrPolicy == RenderLoop::VrrPolicy::Automatic && hasFullscreenSurface)) {
+    if (vrrPolicy == RenderLoop::VrrPolicy::Always || (vrrPolicy == RenderLoop::VrrPolicy::Automatic && fullscreenItem != nullptr)) {
         presentMode = SyncMode::Adaptive;
     } else {
         presentMode = SyncMode::Fixed;
@@ -216,9 +216,9 @@ void RenderLoop::setRefreshRate(int refreshRate)
     Q_EMIT refreshRateChanged();
 }
 
-void RenderLoop::scheduleRepaint()
+void RenderLoop::scheduleRepaint(Item *item)
 {
-    if (d->pendingRepaint) {
+    if (d->pendingRepaint || (d->fullscreenItem != nullptr && item != nullptr && item != d->fullscreenItem)) {
         return;
     }
     if (!d->pendingFrameCount && !d->inhibitCount) {
@@ -238,9 +238,9 @@ std::chrono::nanoseconds RenderLoop::nextPresentationTimestamp() const
     return d->nextPresentationTimestamp;
 }
 
-void RenderLoop::setFullscreenSurface(SurfaceItem *surfaceItem)
+void RenderLoop::setFullscreenSurface(Item *surfaceItem)
 {
-    d->hasFullscreenSurface = surfaceItem != nullptr;
+    d->fullscreenItem = surfaceItem;
 }
 
 RenderLoop::VrrPolicy RenderLoop::vrrPolicy() const

src/renderloop.h

@@ -14,7 +14,7 @@ namespace KWin
 {
 
 class RenderLoopPrivate;
-class SurfaceItem;
+class Item;
 
 /**
  * The RenderLoop class represents the compositing scheduler on a particular output.
@@ -71,7 +71,7 @@ public:
     /**
      * Schedules a compositing cycle at the next available moment.
      */
-    void scheduleRepaint();
+    void scheduleRepaint(Item *item = nullptr);
 
     /**
      * Returns the timestamp of the last frame that has been presented on the screen.
@@ -90,7 +90,7 @@ public:
      * Sets the surface that currently gets scanned out,
      * so that this RenderLoop can adjust its timing behavior to that surface
      */
-    void setFullscreenSurface(SurfaceItem *surface);
+    void setFullscreenSurface(Item *surface);
 
     enum class VrrPolicy : uint32_t {
         Never = 0,

src/renderloop_p.h

@@ -41,7 +41,7 @@ public:
     bool pendingReschedule = false;
     bool pendingRepaint = false;
     RenderLoop::VrrPolicy vrrPolicy = RenderLoop::VrrPolicy::Never;
-    bool hasFullscreenSurface = false;
+    Item *fullscreenItem = nullptr;
 
     enum class SyncMode {
         Fixed,