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, 4 insertions, 0 deletions

diff --git a/src/gui/kernel/qplatformcursor.cpp b/src/gui/kernel/qplatformcursor.cpp
index 6e2c12bf39..a28617cb37 100644
--- a/src/gui/kernel/qplatformcursor.cpp
+++ b/src/gui/kernel/qplatformcursor.cpp
@@ -95,6 +95,10 @@ QList<QPlatformCursor *> QPlatformCursorPrivate::getInstances()
 
     \a windowCursor is a pointer to the QCursor that should be displayed.
 
+    To unset the cursor of \a window, 0 is passed. This means \a window does not have
+    a cursor set and the cursor of a the first parent window which has a cursor explicitly
+    set or the system default cursor should take effect.
+
     \a window is a pointer to the window currently displayed at QCursor::pos(). Note
     that this may be 0 if the current position is not occupied by a displayed widget.