io/router: support cursor changes on Frame events

Add support to Router so that the cursor can be changed with CursorNameOp without any mouse movement.
Enter and Leave events are also delivered as areas change.

Signed-off-by: pierre <pierre.curto@gmail.com>

io/router/pointer.go

@@ -47,6 +47,9 @@ type pointerInfo struct {
 	id       pointer.ID
 	pressed  bool
 	handlers []event.Tag
+	// last tracks the last pointer event received,
+	// used while processing frame events.
+	last pointer.Event
 
 	// entered tracks the tags that contain the pointer.
 	entered []event.Tag
@@ -247,6 +250,10 @@ func (q *pointerQueue) Frame(root *op.Ops, events *handlerEvents) {
 			}
 		}
 	}
+	for i := range q.pointers {
+		p := &q.pointers[i]
+		q.deliverEnterLeaveEvents(p, events, p.last)
+	}
 }
 
 func cancelHandlers(events *handlerEvents, tags ...event.Tag) {
@@ -295,6 +302,7 @@ func (q *pointerQueue) Push(e pointer.Event, events *handlerEvents) {
 		pidx = len(q.pointers) - 1
 	}
 	p := &q.pointers[pidx]
+	p.last = e
 
 	if e.Type == pointer.Move && p.pressed {
 		e.Type = pointer.Drag