scene: Fix animated software cursor not updating

The Item schedules repaints per scene delegate. Currently, there are no
any attached scene delegates when using software cursor, which results in
it freezing as soon as it stops moving.

The issue is addressed by using SceneDelegate instead of RenderLayerDelegate.

The proposed code is not great, but on the other hand, the plan is to
embed the software cursor in the workspace scene if needed.

BUG: 490440

src/compositor_wayland.cpp

@@ -416,9 +416,9 @@ void WaylandCompositor::addOutput(Output *output)
     auto cursorLayer = new RenderLayer(output->renderLoop());
     cursorLayer->setVisible(false);
     if (m_backend->compositingType() == OpenGLCompositing) {
-        cursorLayer->setDelegate(std::make_unique<CursorDelegateOpenGL>(output));
+        cursorLayer->setDelegate(std::make_unique<CursorDelegateOpenGL>(m_cursorScene.get(), output));
     } else {
-        cursorLayer->setDelegate(std::make_unique<CursorDelegateQPainter>(output));
+        cursorLayer->setDelegate(std::make_unique<CursorDelegateQPainter>(m_cursorScene.get(), output));
     }
     cursorLayer->setParent(workspaceLayer);
     cursorLayer->setSuperlayer(workspaceLayer);

src/scene/cursordelegate_opengl.cpp

@@ -21,8 +21,9 @@
 namespace KWin
 {
 
-CursorDelegateOpenGL::CursorDelegateOpenGL(Output *output)
-    : m_output(output)
+CursorDelegateOpenGL::CursorDelegateOpenGL(Scene *scene, Output *output)
+    : SceneDelegate(scene, nullptr)
+    , m_output(output)
 {
 }
 

src/scene/cursordelegate_opengl.h

@@ -5,10 +5,8 @@
 */
 
 #pragma once
-#include <QObject>
-#include <memory>
 
-#include "core/renderlayerdelegate.h"
+#include "scene/scene.h"
 
 namespace KWin
 {
@@ -17,12 +15,12 @@ class GLFramebuffer;
 class GLTexture;
 class Output;
 
-class CursorDelegateOpenGL final : public QObject, public RenderLayerDelegate
+class CursorDelegateOpenGL final : public QObject, public SceneDelegate
 {
     Q_OBJECT
 
 public:
-    CursorDelegateOpenGL(Output *output);
+    CursorDelegateOpenGL(Scene *scene, Output *output);
     ~CursorDelegateOpenGL() override;
 
     void paint(const RenderTarget &renderTarget, const QRegion &region) override;

src/scene/cursordelegate_qpainter.cpp

@@ -18,8 +18,9 @@
 namespace KWin
 {
 
-CursorDelegateQPainter::CursorDelegateQPainter(Output *output)
-    : m_output(output)
+CursorDelegateQPainter::CursorDelegateQPainter(Scene *scene, Output *output)
+    : SceneDelegate(scene, nullptr)
+    , m_output(output)
 {
 }
 

src/scene/cursordelegate_qpainter.h

@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include "core/renderlayerdelegate.h"
+#include "scene/scene.h"
 
 #include <QImage>
 
@@ -15,10 +15,10 @@ namespace KWin
 
 class Output;
 
-class CursorDelegateQPainter final : public RenderLayerDelegate
+class CursorDelegateQPainter final : public SceneDelegate
 {
 public:
-    CursorDelegateQPainter(Output *output);
+    CursorDelegateQPainter(Scene *scene, Output *output);
 
     void paint(const RenderTarget &renderTarget, const QRegion &region) override;
 

src/scene/cursorscene.cpp

@@ -48,7 +48,7 @@ QRegion CursorScene::prePaint(SceneDelegate *delegate)
 {
     resetRepaintsHelper(m_rootItem.get(), delegate);
     m_paintedOutput = delegate->output();
-    return QRegion();
+    return m_rootItem->boundingRect().translated(-delegate->viewport().topLeft()).toAlignedRect();
 }
 
 void CursorScene::postPaint()