Regression: Fix setting of custom cursors for native widgets.

Currently, there is no concept of not having a cursor set on
a Window. Qt::ArrowCursor is always set instead. This causes
bugs when native child widgets are involved, for example setting
a cursor on the native widget's parent no longer works since
the child's Qt::ArrowCursor applies.

Introduce QWindowPrivate::hasCursor tracking whether a cursor
has been explicitly set and clear in QWindow::unsetCursor().

Handle 0 in QPlatformCursor::changeCursor() to mean
"unsetCursor()":
- Windows: Introduce default constructor for QWindowsWindowCursor
  meaning "0". Search for applicable parent cursor in applyCursor.
- XCB: No big changes required, set XCB_CURSOR_NONE for no cursor.
- Other platforms: Assume Qt::ArrowCursor when cursor = 0 is
  passed for now.

Task-number: QTBUG-28879
Change-Id: Id82722592f3cd5fe577a5b64dcc600c85cfea484
Reviewed-by: Jonathan Liu <net147@gmail.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

1 files changed, 18 insertions, 2 deletions

diff --git a/src/plugins/platforms/windows/qwindowscursor.cpp b/src/plugins/platforms/windows/qwindowscursor.cpp
index ac4070a93b..84c82dca45 100644
--- a/src/plugins/platforms/windows/qwindowscursor.cpp
+++ b/src/plugins/platforms/windows/qwindowscursor.cpp
@@ -405,8 +405,12 @@ void QWindowsCursor::changeCursor(QCursor *cursorIn, QWindow *window)
 
     if (QWindowsContext::verboseWindows > 1)
         qDebug() << __FUNCTION__ <<  cursorIn << window;
-    if (!cursorIn || !window)
+    if (!window)
         return;
+    if (!cursorIn) {
+        QWindowsWindow::baseWindowOf(window)->setCursor(QWindowsWindowCursor());
+        return;
+    }
     const QWindowsWindowCursor wcursor =
         cursorIn->shape() == Qt::BitmapCursor ?
         QWindowsWindowCursor(*cursorIn) : standardWindowCursor(cursorIn->shape());
@@ -448,6 +452,7 @@ void QWindowsCursor::setPos(const QPoint &pos)
 class QWindowsWindowCursorData : public QSharedData
 {
 public:
+    QWindowsWindowCursorData() : m_cursor(Qt::ArrowCursor), m_handle(0) {}
     explicit QWindowsWindowCursorData(const QCursor &c);
     ~QWindowsWindowCursorData();
 
@@ -463,7 +468,13 @@ QWindowsWindowCursorData::QWindowsWindowCursorData(const QCursor &c) :
 
 QWindowsWindowCursorData::~QWindowsWindowCursorData()
 {
-    DestroyCursor(m_handle);
+    if (m_handle)
+        DestroyCursor(m_handle);
+}
+
+QWindowsWindowCursor::QWindowsWindowCursor() :
+    m_data(new QWindowsWindowCursorData)
+{
 }
 
 QWindowsWindowCursor::QWindowsWindowCursor(const QCursor &c) :
@@ -487,6 +498,11 @@ QWindowsWindowCursor & QWindowsWindowCursor::operator =(const QWindowsWindowCurs
     return *this;
 }
 
+bool QWindowsWindowCursor::isNull() const
+{
+    return m_data->m_handle == 0;
+}
+
 QCursor QWindowsWindowCursor::cursor() const
 {
     return m_data->m_cursor;