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, 14 insertions, 2 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 190d52776a..aa3bb0ed60 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -2629,6 +2629,13 @@ static inline void applyCursor(QWindow *w, QCursor c)
             cursor->changeCursor(&c, w);
 }
 
+static inline void unsetCursor(QWindow *w)
+{
+    if (const QScreen *screen = w->screen())
+        if (QPlatformCursor *cursor = screen->handle()->cursor())
+            cursor->changeCursor(0, w);
+}
+
 static inline void applyCursor(const QList<QWindow *> &l, const QCursor &c)
 {
     for (int i = 0; i < l.size(); ++i) {
@@ -2642,8 +2649,13 @@ static inline void applyWindowCursor(const QList<QWindow *> &l)
 {
     for (int i = 0; i < l.size(); ++i) {
         QWindow *w = l.at(i);
-        if (w->handle() && w->type() != Qt::Desktop)
-            applyCursor(w, w->cursor());
+        if (w->handle() && w->type() != Qt::Desktop) {
+            if (qt_window_private(w)->hasCursor) {
+                applyCursor(w, w->cursor());
+            } else {
+                unsetCursor(w);
+            }
+        }
     }
 }