[server] Introduce SurfaceInterface::boundingRect()

Summary:
The new method provides a convenient way for determining the rectangle
that bounds the given surface and all of its sub-surfaces. This can be
very handy when determining the effective window geometry.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: apol, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D27828

src/wayland/surface_interface.cpp

@@ -772,6 +772,19 @@ QSize SurfaceInterface::size() const
     return QSize();
 }
 
+QRect SurfaceInterface::boundingRect() const
+{
+    QRect rect(QPoint(0, 0), size());
+
+    const QList<QPointer<SubSurfaceInterface>> subSurfaces = childSubSurfaces();
+    for (const SubSurfaceInterface *subSurface : subSurfaces) {
+        const SurfaceInterface *childSurface = subSurface->surface();
+        rect |= childSurface->boundingRect().translated(subSurface->position());
+    }
+
+    return rect;
+}
+
 QPointer< ShadowInterface > SurfaceInterface::shadow() const
 {
     Q_D();

src/wayland/surface_interface.h

@@ -112,6 +112,14 @@ public:
      * @since 5.3
      **/
     QSize size() const;
+    /**
+     * Returns the rectangle that bounds this surface and all of its sub-surfaces.
+     *
+     * QPoint(0, 0) corresponds to the upper left corner of this surface.
+     *
+     * @since 5.69
+     */
+    QRect boundingRect() const;
 
     /**
      * @returns The SubSurface for this Surface in case there is one.