Client: Fix incorrect decoration size when QT_SCALE_FACTOR is set

[ChangeLog][QPA plugin] Fixed a bug where window decorations were to small for
for the content when QT_SCALE_FACTOR was set.

Fixes: QTBUG-72993
Change-Id: I1ed26e038c27f7c4454a6bcc04f0849e4af789e7
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

3 files changed, 27 insertions, 9 deletions

diff --git a/src/client/qwaylandabstractdecoration.cpp b/src/client/qwaylandabstractdecoration.cpp
index 32fa6e1b5..0f00b9890 100644
--- a/src/client/qwaylandabstractdecoration.cpp
+++ b/src/client/qwaylandabstractdecoration.cpp
@@ -115,16 +115,17 @@ const QImage &QWaylandAbstractDecoration::contentImage()
 {
     Q_D(QWaylandAbstractDecoration);
     if (d->m_isDirty) {
-        //Update the decoration backingstore
+        // Update the decoration backingstore
 
-        const int scale = waylandWindow()->scale();
-        const QSize imageSize = window()->frameGeometry().size() * scale;
+        const int bufferScale = waylandWindow()->scale();
+        const QSize imageSize = waylandWindow()->surfaceSize() * bufferScale;
         d->m_decorationContentImage = QImage(imageSize, QImage::Format_ARGB32_Premultiplied);
-        d->m_decorationContentImage.setDevicePixelRatio(scale);
+        // Only scale by buffer scale, not QT_SCALE_FACTOR etc.
+        d->m_decorationContentImage.setDevicePixelRatio(bufferScale);
         d->m_decorationContentImage.fill(Qt::transparent);
         this->paint(&d->m_decorationContentImage);
 
-        QRegion damage = marginsRegion(window()->geometry().size(), window()->frameMargins());
+        QRegion damage = marginsRegion(waylandWindow()->surfaceSize(), waylandWindow()->frameMargins());
         for (QRect r : damage)
             waylandWindow()->damage(r);
 
diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index e81221fb5..9e95b3068 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -341,7 +341,7 @@ void QWaylandWindow::setGeometry(const QRect &rect)
         sendExposeEvent(exposeGeometry);
 
     if (mShellSurface)
-        mShellSurface->setWindowGeometry(QRect(QPoint(0, 0), window()->frameGeometry().size()));
+        mShellSurface->setWindowGeometry(windowGeometry());
 }
 
 void QWaylandWindow::resizeFromApplyConfigure(const QSize &sizeWithMargins, const QPoint &offset)
@@ -654,6 +654,23 @@ QMargins QWaylandWindow::frameMargins() const
     return QPlatformWindow::frameMargins();
 }
 
+/*!
+ * Size, with decorations (including including eventual shadows) in wl_surface coordinates
+ */
+QSize QWaylandWindow::surfaceSize() const
+{
+    return geometry().marginsAdded(frameMargins()).size();
+}
+
+/*!
+ * Window geometry as defined by the xdg-shell spec (in wl_surface coordinates)
+ * topLeft is where the shadow stops and the decorations border start.
+ */
+QRect QWaylandWindow::windowGeometry() const
+{
+    return QRect(QPoint(), surfaceSize());
+}
+
 QWaylandShellSurface *QWaylandWindow::shellSurface() const
 {
     return mShellSurface;
@@ -848,9 +865,7 @@ void QWaylandWindow::handleMouse(QWaylandInputDevice *inputDevice, const QWaylan
 
 #if QT_CONFIG(cursor)
     if (e.type == QWaylandPointerEvent::Enter) {
-        QRect windowGeometry = window()->frameGeometry();
-        windowGeometry.moveTopLeft({0, 0}); // convert to wayland surface coordinates
-        QRect contentGeometry = windowGeometry.marginsRemoved(frameMargins());
+        QRect contentGeometry = windowGeometry().marginsRemoved(frameMargins());
         if (contentGeometry.contains(e.local.toPoint()))
             restoreMouseCursor(inputDevice);
     }
diff --git a/src/client/qwaylandwindow_p.h b/src/client/qwaylandwindow_p.h
index 146767a1e..0e573f350 100644
--- a/src/client/qwaylandwindow_p.h
+++ b/src/client/qwaylandwindow_p.h
@@ -125,6 +125,8 @@ public:
     void waitForFrameSync();
 
     QMargins frameMargins() const override;
+    QSize surfaceSize() const;
+    QRect windowGeometry() const;
 
     static QWaylandWindow *fromWlSurface(::wl_surface *surface);