Windows: Implement automatic mouse capture in QPA.

Qt expects the mouse to be captured on any button press
until release.

Remove flags to store capture, use WinAPI GetCapture() instead.
Remove setMouseGrabEnabled_sys(), streamline code.

Replacement for the reverted change
6b5bbc531b30d8ece25425e39843c6ae1af1d045 for QTBUG-25977.

Task-number: QTBUG-27132
Task-number: QTBUG-27039
Task-number: QTBUG-25977
Task-number: QTBUG-26962
Change-Id: If86428eabfadcafd16da10f134a419f833185272
Reviewed-by: Qt Doc Bot <qt_docbot@qt-project.org>
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@digia.com>
Reviewed-by: Jørgen Lind <jorgen.lind@nokia.com>

3 files changed, 41 insertions, 23 deletions

diff --git a/src/plugins/platforms/windows/qwindowsmousehandler.cpp b/src/plugins/platforms/windows/qwindowsmousehandler.cpp
index f1e3d70d96..50980100cb 100644
--- a/src/plugins/platforms/windows/qwindowsmousehandler.cpp
+++ b/src/plugins/platforms/windows/qwindowsmousehandler.cpp
@@ -175,9 +175,26 @@ bool QWindowsMouseHandler::translateMouseEvent(QWindow *window, HWND hwnd,
         return true;
     }
     compressMouseMove(&msg);
+    QWindowsWindow *platformWindow = static_cast<QWindowsWindow *>(window->handle());
+    // Qt expects the platform plugin to capture the mouse on
+    // any button press until release.
+    if (!platformWindow->hasMouseCapture()
+        && (msg.message == WM_LBUTTONDOWN || msg.message == WM_MBUTTONDOWN
+            || msg.message == WM_RBUTTONDOWN)) {
+        platformWindow->setMouseGrabEnabled(true);
+        platformWindow->setFlag(QWindowsWindow::AutoMouseCapture);
+        if (QWindowsContext::verboseEvents)
+            qDebug() << "Automatic mouse capture " << window;
+    } else if (platformWindow->hasMouseCapture()
+               && platformWindow->testFlag(QWindowsWindow::AutoMouseCapture)
+               && (msg.message == WM_LBUTTONUP || msg.message == WM_MBUTTONUP
+                   || msg.message == WM_RBUTTONUP)) {
+        platformWindow->setMouseGrabEnabled(false);
+        if (QWindowsContext::verboseEvents)
+            qDebug() << "Releasing automatic mouse capture " << window;
+    }
     // Eat mouse move after size grip drag.
     if (msg.message == WM_MOUSEMOVE) {
-        QWindowsWindow *platformWindow = static_cast<QWindowsWindow *>(window->handle());
         if (platformWindow->testFlag(QWindowsWindow::SizeGripOperation)) {
             MSG mouseMsg;
             while (PeekMessage(&mouseMsg, platformWindow->handle(), WM_MOUSEMOVE, WM_MOUSEMOVE, PM_REMOVE)) ;
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index b43032dc1a..d58d10b4d5 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -696,7 +696,6 @@ QWindowsWindow::QWindowsWindow(QWindow *aWindow, const WindowData &data) :
     m_hdc(0),
     m_windowState(Qt::WindowNoState),
     m_opacity(1.0),
-    m_mouseGrab(false),
     m_cursor(QWindowsScreen::screenOf(aWindow)->windowsCursor()->standardWindowCursor()),
     m_dropTarget(0),
     m_savedStyle(0),
@@ -738,6 +737,8 @@ void QWindowsWindow::destroyWindow()
     if (QWindowsContext::verboseIntegration || QWindowsContext::verboseWindows)
         qDebug() << __FUNCTION__ << this << window() << m_data.hwnd;
     if (m_data.hwnd) { // Stop event dispatching before Window is destroyed.
+        if (hasMouseCapture())
+            setMouseGrabEnabled(false);
         unregisterDropSite();
         QWindowsContext::instance()->removeWindow(m_data.hwnd);
 #ifdef QT_OPENGL_ES_2
@@ -811,6 +812,8 @@ void QWindowsWindow::setVisible(bool visible)
             QWindowSystemInterface::handleExposeEvent(window(),
                                                       QRect(QPoint(), geometry().size()));
         } else {
+            if (hasMouseCapture())
+                setMouseGrabEnabled(false);
             hide_sys();
             QWindowSystemInterface::handleExposeEvent(window(), QRegion());
         }
@@ -1495,29 +1498,27 @@ bool QWindowsWindow::setKeyboardGrabEnabled(bool grab)
 
 bool QWindowsWindow::setMouseGrabEnabled(bool grab)
 {
-    bool result = false;
+    if (QWindowsContext::verboseWindows)
+        qDebug() << __FUNCTION__ << window() << grab;
     if (!m_data.hwnd) {
         qWarning("%s: No handle", __FUNCTION__);
-        return result;
+        return false;
     }
-    if (QWindowsContext::verboseWindows)
-        qDebug() << __FUNCTION__ << window() << grab;
-
-    if (m_mouseGrab != grab) {
-        m_mouseGrab = grab;
-        if (isVisible())
-            setMouseGrabEnabled_sys(grab);
+    if (!isVisible() && grab) {
+        qWarning("%s: Not setting mouse grab for invisible window %s",
+                 __FUNCTION__, qPrintable(window()->objectName()));
+        return false;
     }
-    return grab;
-}
-
-void QWindowsWindow::setMouseGrabEnabled_sys(bool grab)
-{
-    if (grab) {
-        SetCapture(m_data.hwnd);
-    } else {
-        ReleaseCapture();
+    // release grab or an explicit grab overriding autocapture: Clear flag.
+    clearFlag(QWindowsWindow::AutoMouseCapture);
+    if (hasMouseCapture() != grab) {
+        if (grab) {
+            SetCapture(m_data.hwnd);
+        } else {
+            ReleaseCapture();
+        }
     }
+    return grab;
 }
 
 static inline DWORD cornerToWinOrientation(Qt::Corner corner)
diff --git a/src/plugins/platforms/windows/qwindowswindow.h b/src/plugins/platforms/windows/qwindowswindow.h
index 35790e2739..2bcca8710f 100644
--- a/src/plugins/platforms/windows/qwindowswindow.h
+++ b/src/plugins/platforms/windows/qwindowswindow.h
@@ -126,7 +126,8 @@ public:
         SizeGripOperation = 0x100,
         FrameStrutEventsEnabled = 0x200,
         SynchronousGeometryChangeEvent = 0x400,
-        WithinSetStyle = 0x800
+        WithinSetStyle = 0x800,
+        AutoMouseCapture = 0x1000 //! Automatic mouse capture on button press.
     };
 
     struct WindowData
@@ -179,6 +180,7 @@ public:
 
     virtual bool setKeyboardGrabEnabled(bool grab);
     virtual bool setMouseGrabEnabled(bool grab);
+    inline bool hasMouseCapture() const { return GetCapture() == m_data.hwnd; }
 
     virtual bool startSystemResize(const QPoint &pos, Qt::Corner corner);
 
@@ -249,7 +251,6 @@ private:
     inline bool isFullScreen_sys() const;
     inline void setWindowState_sys(Qt::WindowState newState);
     inline void setParent_sys(const QPlatformWindow *parent) const;
-    inline void setMouseGrabEnabled_sys(bool grab);
     void destroyWindow();
     void registerDropSite();
     void unregisterDropSite();
@@ -261,7 +262,6 @@ private:
     HDC m_hdc;
     Qt::WindowState m_windowState;
     qreal m_opacity;
-    bool m_mouseGrab;
     QWindowsWindowCursor m_cursor;
     QWindowsOleDropTarget *m_dropTarget;
     unsigned m_savedStyle;