3 files changed, 29 insertions, 0 deletions
diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index fc04d6afc4..bf1fd2e177 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -2102,6 +2102,15 @@ void QXcbWindow::handleConfigureNotifyEvent(const xcb_configure_notify_event_t *
     // will make the comparison later.
     QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->screen());
 
+    // Send the synthetic expose event on resize only when the window is shrinked,
+    // because the "XCB_GRAVITY_NORTH_WEST" flag doesn't send it automatically.
+    if (!m_oldWindowSize.isEmpty()
+            && (actualGeometry.width() < m_oldWindowSize.width()
+                || actualGeometry.height() < m_oldWindowSize.height())) {
+        QWindowSystemInterface::handleExposeEvent(window(), QRegion(0, 0, actualGeometry.width(), actualGeometry.height()));
+    }
+    m_oldWindowSize = actualGeometry.size();
+
     if (m_usingSyncProtocol && m_syncState == SyncReceived)
         m_syncState = SyncAndConfigureReceived;
 
diff --git a/src/plugins/platforms/xcb/qxcbwindow.h b/src/plugins/platforms/xcb/qxcbwindow.h
index 9ad0153ca2..e7190b1733 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.h
+++ b/src/plugins/platforms/xcb/qxcbwindow.h
@@ -256,6 +256,7 @@ protected:
     mutable QMargins m_frameMargins;
 
     QRegion m_exposeRegion;
+    QSize m_oldWindowSize;
 
     xcb_visualid_t m_visualId;
     int m_lastWindowStateEvent;
diff --git a/tests/auto/gui/kernel/qwindow/tst_qwindow.cpp b/tests/auto/gui/kernel/qwindow/tst_qwindow.cpp
index 892dc0899f..70446e803a 100644
--- a/tests/auto/gui/kernel/qwindow/tst_qwindow.cpp
+++ b/tests/auto/gui/kernel/qwindow/tst_qwindow.cpp
@@ -58,6 +58,7 @@ private slots:
     void setVisible();
     void eventOrderOnShow();
     void resizeEventAfterResize();
+    void exposeEventOnShrink_QTBUG54040();
     void mapGlobal();
     void positioning_data();
     void positioning();
@@ -373,6 +374,24 @@ void tst_QWindow::resizeEventAfterResize()
     QTRY_COMPARE(window.received(QEvent::Resize), 2);
 }
 
+void tst_QWindow::exposeEventOnShrink_QTBUG54040()
+{
+    Window window;
+    window.setGeometry(QRect(m_availableTopLeft + QPoint(80, 80), m_testWindowSize));
+    window.setTitle(QTest::currentTestFunction());
+    window.showNormal();
+
+    QVERIFY(QTest::qWaitForWindowExposed(&window));
+
+    const int initialExposeCount = window.received(QEvent::Expose);
+    window.resize(window.width(), window.height() - 5);
+    QTRY_COMPARE(window.received(QEvent::Expose), initialExposeCount + 1);
+    window.resize(window.width() - 5, window.height());
+    QTRY_COMPARE(window.received(QEvent::Expose), initialExposeCount + 2);
+    window.resize(window.width() - 5, window.height() - 5);
+    QTRY_COMPARE(window.received(QEvent::Expose), initialExposeCount + 3);
+}
+
 void tst_QWindow::positioning_data()
 {
     QTest::addColumn<int>("windowflags");