scene: Add SurfaceItem::destinationSize()

Its main purpose is to reroute surface size updates through SurfaceItem
so it can invalidate quads cache. Not all SurfaceItems currently discard
them when needed. When proper item transform support lands,
setDestinationSize() could also change the surface scale instead.

src/scene/itemrenderer_qpainter.cpp

@@ -140,7 +140,7 @@ void ItemRendererQPainter::renderSurfaceItem(QPainter *painter, SurfaceItem *sur
     surfaceItem->resetDamage();
 
     const OutputTransform surfaceToBufferTransform = surfaceItem->bufferTransform();
-    const QSizeF transformedSize = surfaceToBufferTransform.map(surfaceItem->size());
+    const QSizeF transformedSize = surfaceToBufferTransform.map(surfaceItem->destinationSize());
 
     painter->save();
     switch (surfaceToBufferTransform.kind()) {

src/scene/surfaceitem.cpp

@@ -16,6 +16,20 @@ SurfaceItem::SurfaceItem(Scene *scene, Item *parent)
 {
 }
 
+QSizeF SurfaceItem::destinationSize() const
+{
+    return m_destinationSize;
+}
+
+void SurfaceItem::setDestinationSize(const QSizeF &size)
+{
+    if (m_destinationSize != size) {
+        m_destinationSize = size;
+        setSize(size);
+        discardQuads();
+    }
+}
+
 QRectF SurfaceItem::bufferSourceBox() const
 {
     return m_bufferSourceBox;
@@ -60,8 +74,8 @@ void SurfaceItem::setBufferSize(const QSize &size)
 QRegion SurfaceItem::mapFromBuffer(const QRegion &region) const
 {
     const QRectF sourceBox = m_bufferToSurfaceTransform.map(m_bufferSourceBox, m_bufferSize);
-    const qreal xScale = size().width() / sourceBox.width();
-    const qreal yScale = size().height() / sourceBox.height();
+    const qreal xScale = m_destinationSize.width() / sourceBox.width();
+    const qreal yScale = m_destinationSize.height() / sourceBox.height();
 
     QRegion result;
     for (QRectF rect : region) {
@@ -100,8 +114,8 @@ void SurfaceItem::addDamage(const QRegion &region)
     m_damage += region;
 
     const QRectF sourceBox = m_bufferToSurfaceTransform.map(m_bufferSourceBox, m_bufferSize);
-    const qreal xScale = sourceBox.width() / size().width();
-    const qreal yScale = sourceBox.height() / size().height();
+    const qreal xScale = sourceBox.width() / m_destinationSize.width();
+    const qreal yScale = sourceBox.height() / m_destinationSize.height();
     const QRegion logicalDamage = mapFromBuffer(region);
 
     const auto delegates = scene()->delegates();
@@ -214,8 +228,8 @@ WindowQuadList SurfaceItem::buildQuads() const
     quads.reserve(region.count());
 
     const QRectF sourceBox = m_bufferToSurfaceTransform.map(m_bufferSourceBox, m_bufferSize);
-    const qreal xScale = sourceBox.width() / size().width();
-    const qreal yScale = sourceBox.height() / size().height();
+    const qreal xScale = sourceBox.width() / m_destinationSize.width();
+    const qreal yScale = sourceBox.height() / m_destinationSize.height();
 
     for (const QRectF rect : region) {
         WindowQuad quad;

src/scene/surfaceitem.h

@@ -26,6 +26,9 @@ class KWIN_EXPORT SurfaceItem : public Item
     Q_OBJECT
 
 public:
+    QSizeF destinationSize() const;
+    void setDestinationSize(const QSizeF &size);
+
     QRectF bufferSourceBox() const;
     void setBufferSourceBox(const QRectF &box);
 
@@ -72,6 +75,7 @@ protected:
     OutputTransform m_surfaceToBufferTransform;
     QRectF m_bufferSourceBox;
     QSize m_bufferSize;
+    QSizeF m_destinationSize;
     std::unique_ptr<SurfacePixmap> m_pixmap;
     std::unique_ptr<SurfacePixmap> m_previousPixmap;
     int m_referencePixmapCounter = 0;

src/scene/surfaceitem_internal.cpp

@@ -19,7 +19,7 @@ SurfaceItemInternal::SurfaceItemInternal(InternalWindow *window, Scene *scene, I
     connect(window, &Window::bufferGeometryChanged,
             this, &SurfaceItemInternal::handleBufferGeometryChanged);
 
-    setSize(window->bufferGeometry().size());
+    setDestinationSize(window->bufferGeometry().size());
     setBufferSourceBox(QRectF(QPointF(0, 0), window->bufferGeometry().size() * window->bufferScale()));
     setBufferSize((window->bufferGeometry().size() * window->bufferScale()).toSize());
 }
@@ -41,7 +41,7 @@ std::unique_ptr<SurfacePixmap> SurfaceItemInternal::createPixmap()
 
 void SurfaceItemInternal::handleBufferGeometryChanged()
 {
-    setSize(m_window->bufferGeometry().size());
+    setDestinationSize(m_window->bufferGeometry().size());
     setBufferSourceBox(QRectF(QPointF(0, 0), m_window->bufferGeometry().size() * m_window->bufferScale()));
     setBufferSize((m_window->bufferGeometry().size() * m_window->bufferScale()).toSize());
 }

src/scene/surfaceitem_wayland.cpp

@@ -55,7 +55,7 @@ SurfaceItemWayland::SurfaceItemWayland(SurfaceInterface *surface, Scene *scene,
     }
 
     handleChildSubSurfacesChanged();
-    setSize(surface->size());
+    setDestinationSize(surface->size());
     setBufferTransform(surface->bufferTransform());
     setBufferSourceBox(surface->bufferSourceBox());
     setBufferSize(surface->bufferSize());
@@ -82,8 +82,7 @@ SurfaceInterface *SurfaceItemWayland::surface() const
 
 void SurfaceItemWayland::handleSurfaceSizeChanged()
 {
-    setSize(m_surface->size());
-    discardQuads();
+    setDestinationSize(m_surface->size());
 }
 
 void SurfaceItemWayland::handleBufferSizeChanged()

src/scene/surfaceitem_x11.cpp

@@ -34,7 +34,7 @@ SurfaceItemX11::SurfaceItemX11(X11Window *window, Scene *scene, Item *parent)
         m_isDamaged = true;
     }
 
-    setSize(window->bufferGeometry().size());
+    setDestinationSize(window->bufferGeometry().size());
     setBufferSourceBox(QRectF(QPointF(0, 0), window->bufferGeometry().size()));
     setBufferSize(window->bufferGeometry().size().toSize());
 }
@@ -142,7 +142,7 @@ void SurfaceItemX11::destroyDamage()
 
 void SurfaceItemX11::handleBufferGeometryChanged()
 {
-    setSize(m_window->bufferGeometry().size());
+    setDestinationSize(m_window->bufferGeometry().size());
     setBufferSourceBox(QRectF(QPointF(0, 0), m_window->bufferGeometry().size()));
     setBufferSize(m_window->bufferGeometry().size().toSize());
 }