platform/drm: Fix clipped HiDPI hardware cursors

If an output is rotated, we will compute a transform matrix for the
cursor plane to rotate its contents.

In order to compute that matrix we need the rect of the cursor in the
device-independent pixels, the scale factor and the output transform.

The problem is that we provide a rect of the cursor in the native
pixels. This may result in the cursor being partially or fully clipped.

CCBUG: 424589

cursor.cpp

@@ -147,6 +147,11 @@ QRect Cursor::geometry() const
     return QRect(m_pos - hotspot(), image().size());
 }
 
+QRect Cursor::rect() const
+{
+    return QRect(QPoint(0, 0), image().size() / image().devicePixelRatio());
+}
+
 QPoint Cursor::pos()
 {
     doGetPos();

cursor.h

@@ -163,6 +163,7 @@ public:
     QImage image() const { return m_image; }
     QPoint hotspot() const { return m_hotspot; }
     QRect geometry() const;
+    QRect rect() const;
 
     void updateCursor(const QImage &image, const QPoint &hotspot);
     void markAsRendered() {

plugins/platforms/drm/drm_output.cpp

@@ -136,7 +136,8 @@ void DrmOutput::updateCursor()
     if (m_deleted) {
         return;
     }
-    QImage cursorImage = Cursors::self()->currentCursor()->image();
+    const Cursor *cursor = Cursors::self()->currentCursor();
+    const QImage cursorImage = cursor->image();
     if (cursorImage.isNull()) {
         return;
     }
@@ -146,14 +147,14 @@ void DrmOutput::updateCursor()
 
     QPainter p;
     p.begin(c);
-    p.setWorldTransform(logicalToNativeMatrix(cursorImage.rect(), scale(), transform()).toTransform());
+    p.setWorldTransform(logicalToNativeMatrix(cursor->rect(), scale(), transform()).toTransform());
     p.drawImage(QPoint(0, 0), cursorImage);
     p.end();
 }
 
 void DrmOutput::moveCursor(Cursor *cursor, const QPoint &globalPos)
 {
-    const QMatrix4x4 hotspotMatrix = logicalToNativeMatrix(cursor->image().rect(), scale(), transform());
+    const QMatrix4x4 hotspotMatrix = logicalToNativeMatrix(cursor->rect(), scale(), transform());
     const QMatrix4x4 monitorMatrix = logicalToNativeMatrix(geometry(), scale(), transform());
 
     QPoint pos = monitorMatrix.map(globalPos);

plugins/scenes/opengl/scene_opengl.cpp

@@ -568,8 +568,7 @@ void SceneOpenGL2::paintCursor(const QRegion &rendered)
 
     // figure out which part of the cursor needs to be repainted
     const QPoint cursorPos = cursor->pos() - cursor->hotspot();
-    const qreal scale = cursor->image().devicePixelRatio();
-    const QRect cursorRect(QPoint(0, 0), cursor->image().size() / scale);
+    const QRect cursorRect = cursor->rect();
     QRegion region;
     for (const QRect &rect : rendered) {
         region |= rect.translated(-cursorPos).intersected(cursorRect);