Client: Send exposeEvent to parent on subsurface position changes

When a subsurface is moved, we need the parent window to commit to apply
that move. Ideally we want this in sync with any potential rendering on
the parent window.

Currently the code calls requestUpdate() which acts more like a frame
callback; it will only do something if the main QWindow considers itself
dirty.

We want to force a repaint, which is semantically more similar to an
ExposeEvent.

Fixes: QTBUG-86177
Change-Id: I30bdfa357beee860ce2b00a256eaea6d040dd55c
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
(cherry picked from commit b36a345d727eab37ee4ec4c2dc4674d5971c81d8)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 34 insertions, 6 deletions

diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index fd3cc4963..d32b4fce3 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -342,7 +342,12 @@ void QWaylandWindow::setGeometry_helper(const QRect &rect)
     if (mSubSurfaceWindow) {
         QMargins m = QPlatformWindow::parent()->frameMargins();
         mSubSurfaceWindow->set_position(rect.x() + m.left(), rect.y() + m.top());
-        mSubSurfaceWindow->parent()->window()->requestUpdate();
+
+        QWaylandWindow *parentWindow = mSubSurfaceWindow->parent();
+        if (parentWindow && parentWindow->isExposed()) {
+            QRect parentExposeGeometry(QPoint(), parentWindow->geometry().size());
+            parentWindow->sendExposeEvent(parentExposeGeometry);
+        }
     }
 }
 
diff --git a/tests/auto/client/surface/tst_surface.cpp b/tests/auto/client/surface/tst_surface.cpp
index b8a65f159..95e4e6098 100644
--- a/tests/auto/client/surface/tst_surface.cpp
+++ b/tests/auto/client/surface/tst_surface.cpp
@@ -167,17 +167,40 @@ void tst_surface::negotiateShmFormat()
 void tst_surface::createSubsurface()
 {
     QRasterWindow window;
-    window.resize(64, 64);
-    window.show();
-    QCOMPOSITOR_TRY_VERIFY(xdgToplevel());
-    exec([=] { xdgToplevel()->sendCompleteConfigure(); });
-    QCOMPOSITOR_TRY_VERIFY(xdgSurface()->m_committedConfigureSerial);
+    window.setObjectName("main");
+    window.resize(200, 200);
 
     QRasterWindow subWindow;
+    subWindow.setObjectName("subwindow");
     subWindow.setParent(&window);
     subWindow.resize(64, 64);
+
+    window.show();
     subWindow.show();
+
     QCOMPOSITOR_TRY_VERIFY(subSurface());
+    QCOMPOSITOR_TRY_VERIFY(xdgToplevel());
+    exec([=] { xdgToplevel()->sendCompleteConfigure(); });
+    QCOMPOSITOR_TRY_VERIFY(xdgSurface()->m_committedConfigureSerial);
+
+    const Surface *mainSurface = exec([=] {return surface(0);});
+    const Surface *childSurface = exec([=] {return surface(1);});
+    QSignalSpy  mainSurfaceCommitSpy(mainSurface, &Surface::commit);
+    QSignalSpy childSurfaceCommitSpy(childSurface, &Surface::commit);
+
+    // Move subsurface. The parent should redraw and commit
+    subWindow.setGeometry(100, 100, 64, 64);
+    // the toplevel should commit to indicate the subsurface moved
+    QCOMPOSITOR_TRY_COMPARE(mainSurfaceCommitSpy.count(), 1);
+    mainSurfaceCommitSpy.clear();
+    childSurfaceCommitSpy.clear();
+
+    // Move and resize the subSurface. The parent should redraw and commit
+    // The child should also redraw
+    subWindow.setGeometry(50, 50, 80, 80);
+    QCOMPOSITOR_TRY_COMPARE(mainSurfaceCommitSpy.count(), 1);
+    QCOMPOSITOR_TRY_COMPARE(childSurfaceCommitSpy.count(), 1);
+
 }
 
 // Used to cause a crash in libwayland (QTBUG-79674)