[server] Respect input region of sub-surfaces on pointer surface focus

Summary:
KWayland takes always the top-most child surface at a given position for its
pointer input. But if a sub-surface sets its input region, it should not select
this one when the position is out of its input region, but rather try the
surface below.

Test Plan:
My testing was only on my Xwayland branch. Supposed to also fix a problem
with Firefox native Wayland port.

Reviewers: #frameworks, graesslin, davidedmundson

Reviewed By: davidedmundson

Subscribers: davidedmundson, zzag, kde-frameworks-devel, graesslin, plasma-devel

Tags: #frameworks, #plasma_on_wayland

Differential Revision: https://phabricator.kde.org/D7038

src/wayland/pointer_interface.cpp

@@ -241,7 +241,7 @@ PointerInterface::PointerInterface(SeatInterface *parent, wl_resource *parentRes
                 return;
             }
             const QPointF pos = d->seat->focusedPointerSurfaceTransformation().map(d->seat->pointerPos());
-            auto targetSurface = d->focusedSurface->surfaceAt(pos);
+            auto targetSurface = d->focusedSurface->inputSurfaceAt(pos);
             if (!targetSurface) {
                 targetSurface = d->focusedSurface;
             }
@@ -286,7 +286,7 @@ void PointerInterface::setFocusedSurface(SurfaceInterface *surface, quint32 seri
     );
 
     const QPointF pos = d->seat->focusedPointerSurfaceTransformation().map(d->seat->pointerPos());
-    d->focusedChildSurface = QPointer<SurfaceInterface>(d->focusedSurface->surfaceAt(pos));
+    d->focusedChildSurface = QPointer<SurfaceInterface>(d->focusedSurface->inputSurfaceAt(pos));
     if (!d->focusedChildSurface) {
         d->focusedChildSurface = QPointer<SurfaceInterface>(d->focusedSurface);
     }

src/wayland/surface_interface.cpp

@@ -856,6 +856,35 @@ SurfaceInterface *SurfaceInterface::surfaceAt(const QPointF &position)
     return nullptr;
 }
 
+SurfaceInterface *SurfaceInterface::inputSurfaceAt(const QPointF &position)
+{
+    // TODO: Most of this is very similar to SurfaceInterface::surfaceAt
+    //       Is there a way to reduce the code duplication?
+    if (!isMapped()) {
+        return nullptr;
+    }
+    Q_D();
+    // go from top to bottom. Top most child is last in list
+    QListIterator<QPointer<SubSurfaceInterface>> it(d->current.children);
+    it.toBack();
+    while (it.hasPrevious()) {
+        const auto &current = it.previous();
+        auto surface = current->surface();
+        if (surface.isNull()) {
+            continue;
+        }
+        if (auto s = surface->inputSurfaceAt(position - current->position())) {
+            return s;
+        }
+    }
+    // check whether the geometry and input region contain the pos
+    if (!size().isEmpty() && QRectF(QPoint(0, 0), size()).contains(position) &&
+            (inputIsInfinite() || input().contains(position.toPoint()))) {
+        return this;
+    }
+    return nullptr;
+}
+
 QPointer<LockedPointerInterface> SurfaceInterface::lockedPointer() const
 {
     Q_D();

src/wayland/surface_interface.h

@@ -211,6 +211,21 @@ public:
      **/
     SurfaceInterface *surfaceAt(const QPointF &position);
 
+    /**
+     * Finds the input receiving SurfaceInterface at the given @p position in surface-local coordinates.
+     * This can be either a descendant SurfaceInterface honoring the stacking order or
+     * the SurfaceInterface itself if its geometry contains the given @p position.
+     *
+     * If no such SurfaceInterface is found, e.g. because the SurfaceInterface is unmapped or there is no
+     * input region containing the position,
+     * @c nullptr is returned.
+     *
+     * @param position The position in surface-local coordinates
+     * @returns Input receiving child surface at the given @p position or surface itself at the position, might be @c nullptr
+     * @since 5.52
+     **/
+    SurfaceInterface *inputSurfaceAt(const QPointF &position);
+
     /**
      * Sets the @p outputs this SurfaceInterface overlaps with, may be empty.
      *