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>

1 files changed, 18 insertions, 1 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)) ;