The Drag&Drop functionality had stopped working with touchscreen/pen
after the WM_POINTER-based input handling was added. The Drag&Drop
functionality internally uses the DoDragDrop() WIN32 call which,
according to Microsoft docs, is not supported for invocation inside
handlers for touch/pen messages, and should be invoked in handlers
for mouse messages that are synthesized by the OS afterwards. The
result was that when DoDragDrop (which is a blocking function with
its own event loop) was called it would hang ignoring all touch/pen
messages until a mouse/touchpad message arrived. This change
implements a workaround for this issue by enqueuing Qt touch/pen
events that would be generated inside the pointer message handler,
and that could start a Drag&Drop operation, and only producing them
after the OS sends the associated mouse messages.
Task-number: QTBUG-70887
Change-Id: Id45e0ecc70358ba250de9b3268856781ed21c9dd
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
83d56811ec