io/router: drop the correct handlers when a pointer grab is requested

Fixes gio#208

Signed-off-by: Elias Naur <mail@eliasnaur.com>

io/router/pointer.go

@@ -239,10 +239,11 @@ func (q *pointerQueue) Frame(root *op.Ops, events *handlerEvents) {
 				for i, k2 := range p.handlers {
 					if k2 == k {
 						// Drop other handlers that lost their grab.
-						cancelHandlers(events, p.handlers[i+1:]...)
-						cancelHandlers(events, p.handlers[:i]...)
-						q.dropHandlers(events, p.handlers[i+1:]...)
-						q.dropHandlers(events, p.handlers[:i]...)
+						dropped := make([]event.Tag, 0, len(p.handlers)-1)
+						dropped = append(dropped, p.handlers[:i]...)
+						dropped = append(dropped, p.handlers[i+1:]...)
+						cancelHandlers(events, dropped...)
+						q.dropHandlers(events, dropped...)
 						break
 					}
 				}

io/router/pointer_test.go

@@ -79,6 +79,41 @@ func TestPointerDragNegative(t *testing.T) {
 	assertEventSequence(t, r.Events(handler), pointer.Cancel, pointer.Enter, pointer.Press, pointer.Leave, pointer.Drag)
 }
 
+func TestPointerGrab(t *testing.T) {
+	handler1 := new(int)
+	handler2 := new(int)
+	handler3 := new(int)
+	var ops op.Ops
+
+	types := pointer.Press | pointer.Release
+
+	pointer.InputOp{Tag: handler1, Types: types, Grab: true}.Add(&ops)
+	pointer.InputOp{Tag: handler2, Types: types}.Add(&ops)
+	pointer.InputOp{Tag: handler3, Types: types}.Add(&ops)
+
+	var r Router
+	r.Frame(&ops)
+	r.Queue(
+		pointer.Event{
+			Type:     pointer.Press,
+			Position: f32.Pt(50, 50),
+		},
+	)
+	assertEventSequence(t, r.Events(handler1), pointer.Cancel, pointer.Press)
+	assertEventSequence(t, r.Events(handler2), pointer.Cancel, pointer.Press)
+	assertEventSequence(t, r.Events(handler3), pointer.Cancel, pointer.Press)
+	r.Frame(&ops)
+	r.Queue(
+		pointer.Event{
+			Type:     pointer.Release,
+			Position: f32.Pt(50, 50),
+		},
+	)
+	assertEventSequence(t, r.Events(handler1), pointer.Release)
+	assertEventSequence(t, r.Events(handler2), pointer.Cancel)
+	assertEventSequence(t, r.Events(handler3), pointer.Cancel)
+}
+
 func TestPointerMove(t *testing.T) {
 	handler1 := new(int)
 	handler2 := new(int)