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, 8 insertions, 2 deletions

diff --git a/src/widgets/kernel/qwidget_qpa.cpp b/src/widgets/kernel/qwidget_qpa.cpp
index 2aee80ade4..2c2d912009 100644
--- a/src/widgets/kernel/qwidget_qpa.cpp
+++ b/src/widgets/kernel/qwidget_qpa.cpp
@@ -999,6 +999,12 @@ static inline void applyCursor(QWidget *w, QCursor c)
         window->setCursor(c);
 }
 
+static inline void unsetCursor(QWidget *w)
+{
+    if (QWindow *window = w->windowHandle())
+        window->unsetCursor();
+}
+
 void qt_qpa_set_cursor(QWidget *w, bool force)
 {
     if (!w->testAttribute(Qt::WA_WState_Created))
@@ -1032,9 +1038,9 @@ void qt_qpa_set_cursor(QWidget *w, bool force)
         else
             // Enforce the windows behavior of clearing the cursor on
             // disabled widgets.
-            applyCursor(nativeParent, Qt::ArrowCursor);
+            unsetCursor(nativeParent);
     } else {
-        applyCursor(nativeParent, Qt::ArrowCursor);
+        unsetCursor(nativeParent);
     }
 }
 #endif //QT_NO_CURSOR