QPlatformCursor: Add functions for setting/clearing override cursors

QPA is modeled on the assumption that the cursor is a property
of the window and therefore sets the override cursors on all windows.
However, on macOS and Windows, the cursor is set per application (or
screen). On these platforms, the per window cursor setting needs
to be emulated which is a source of bugs especially for override
cursors.

Add new virtuals to QPlatformCursor allowing to set override
cursors which can be implemented by directly setting the cursor
on those platforms.

Task-number: QTBUG-40122
Task-number: QTBUG-61133
Change-Id: I31d6a927128d22bb1620a8ace35988c0e126236e
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@qt.io>
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@qt.io>

3 files changed, 36 insertions, 3 deletions

diff --git a/src/plugins/platforms/windows/qwindowscursor.cpp b/src/plugins/platforms/windows/qwindowscursor.cpp
index 1bebe88df7..b9c320fd8f 100644
--- a/src/plugins/platforms/windows/qwindowscursor.cpp
+++ b/src/plugins/platforms/windows/qwindowscursor.cpp
@@ -586,6 +586,13 @@ QWindowsCursor::QWindowsCursor(const QPlatformScreen *screen)
     Q_UNUSED(dummy)
 }
 
+inline CursorHandlePtr QWindowsCursor::cursorHandle(const QCursor &cursor)
+{
+    return cursor.shape() == Qt::BitmapCursor
+        ? pixmapWindowCursor(cursor)
+        : standardWindowCursor(cursor.shape());
+}
+
 /*!
     \brief Set a cursor on a window.
 
@@ -603,9 +610,7 @@ void QWindowsCursor::changeCursor(QCursor *cursorIn, QWindow *window)
         platformWindow->setCursor(CursorHandlePtr(new CursorHandle));
         return;
     }
-    const CursorHandlePtr wcursor =
-        cursorIn->shape() == Qt::BitmapCursor ?
-        pixmapWindowCursor(*cursorIn) : standardWindowCursor(cursorIn->shape());
+    const CursorHandlePtr wcursor = cursorHandle(*cursorIn);
     if (wcursor->handle()) {
         platformWindow->setCursor(wcursor);
     } else {
@@ -614,6 +619,25 @@ void QWindowsCursor::changeCursor(QCursor *cursorIn, QWindow *window)
     }
 }
 
+void QWindowsCursor::setOverrideCursor(const QCursor &cursor)
+{
+    const CursorHandlePtr wcursor = cursorHandle(cursor);
+    if (wcursor->handle()) {
+        m_overriddenCursor = SetCursor(wcursor->handle());
+    } else {
+        qWarning("%s: Unable to obtain system cursor for %d",
+                 __FUNCTION__, cursor.shape());
+    }
+}
+
+void QWindowsCursor::clearOverrideCursor()
+{
+    if (m_overriddenCursor) {
+        SetCursor(m_overriddenCursor);
+        m_overriddenCursor = nullptr;
+    }
+}
+
 QPoint QWindowsCursor::mousePosition()
 {
     POINT p;
diff --git a/src/plugins/platforms/windows/qwindowscursor.h b/src/plugins/platforms/windows/qwindowscursor.h
index df2e22733b..9aa9523ac8 100644
--- a/src/plugins/platforms/windows/qwindowscursor.h
+++ b/src/plugins/platforms/windows/qwindowscursor.h
@@ -105,6 +105,9 @@ public:
     explicit QWindowsCursor(const QPlatformScreen *screen);
 
     void changeCursor(QCursor * widgetCursor, QWindow * widget) override;
+    void setOverrideCursor(const QCursor &cursor) override;
+    void clearOverrideCursor() override;
+
     QPoint pos() const override;
     void setPos(const QPoint &pos) override;
 
@@ -127,6 +130,8 @@ private:
     typedef QHash<Qt::CursorShape, CursorHandlePtr> StandardCursorCache;
     typedef QHash<QWindowsPixmapCursorCacheKey, CursorHandlePtr> PixmapCursorCache;
 
+    CursorHandlePtr cursorHandle(const QCursor &c);
+
     const QPlatformScreen *const m_screen;
     StandardCursorCache m_standardCursorCache;
     PixmapCursorCache m_pixmapCursorCache;
@@ -135,6 +140,8 @@ private:
     mutable QPixmap m_moveDragCursor;
     mutable QPixmap m_linkDragCursor;
     mutable QPixmap m_ignoreDragCursor;
+
+    HCURSOR m_overriddenCursor = nullptr;
 };
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index 6c8fccf350..eb7ad5ecd8 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/src/plugins/platforms/windows/qwindowsintegration.cpp
@@ -72,6 +72,7 @@
 #include <QtGui/private/qguiapplication_p.h>
 #include <QtGui/private/qhighdpiscaling_p.h>
 #include <QtGui/qpa/qplatforminputcontextfactory_p.h>
+#include <QtGui/qpa/qplatformcursor.h>
 
 #include <QtEventDispatcherSupport/private/qwindowsguieventdispatcher_p.h>
 
@@ -242,6 +243,7 @@ QWindowsIntegrationPrivate::QWindowsIntegrationPrivate(const QStringList &paramL
     }
 
     m_context.initTouch(m_options);
+    QPlatformCursor::setCapability(QPlatformCursor::OverrideCursor);
 }
 
 QWindowsIntegrationPrivate::~QWindowsIntegrationPrivate()