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, 13 insertions, 11 deletions

diff --git a/src/plugins/platforms/xcb/qxcbcursor.cpp b/src/plugins/platforms/xcb/qxcbcursor.cpp
index e2843d04dc..0704ab6205 100644
--- a/src/plugins/platforms/xcb/qxcbcursor.cpp
+++ b/src/plugins/platforms/xcb/qxcbcursor.cpp
@@ -301,17 +301,19 @@ void QXcbCursor::changeCursor(QCursor *cursor, QWindow *widget)
         // No X11 cursor control when there is no widget under the cursor
         return;
     
-    xcb_cursor_t c;
-    if (cursor->shape() == Qt::BitmapCursor) {
-        qint64 id = cursor->pixmap().cacheKey();
-        if (!m_bitmapCursorMap.contains(id))
-            m_bitmapCursorMap.insert(id, createBitmapCursor(cursor));
-        c = m_bitmapCursorMap.value(id);
-    } else {
-        int id = cursor->shape();
-        if (!m_shapeCursorMap.contains(id))
-            m_shapeCursorMap.insert(id, createFontCursor(cursor->shape()));
-        c = m_shapeCursorMap.value(id);
+    xcb_cursor_t c = XCB_CURSOR_NONE;
+    if (cursor) {
+        if (cursor->shape() == Qt::BitmapCursor) {
+            qint64 id = cursor->pixmap().cacheKey();
+            if (!m_bitmapCursorMap.contains(id))
+                m_bitmapCursorMap.insert(id, createBitmapCursor(cursor));
+            c = m_bitmapCursorMap.value(id);
+        } else {
+            int id = cursor->shape();
+            if (!m_shapeCursorMap.contains(id))
+                m_shapeCursorMap.insert(id, createFontCursor(cursor->shape()));
+            c = m_shapeCursorMap.value(id);
+        }
     }
 
     w->setCursor(c);