io/pointer: add Drag event type

This eliminates needless redraws for handlers that care about drag events and not move events, like gesture.Scroll.

Signed-off-by: Gordon Klaus <gordon.klaus@gmail.com>

gesture/gesture.go

@@ -174,7 +174,7 @@ func (s *Scroll) Add(ops *op.Ops) {
 	oph := pointer.InputOp{
 		Tag:   s,
 		Grab:  s.grab,
-		Types: pointer.Press | pointer.Move | pointer.Release | pointer.Scroll,
+		Types: pointer.Press | pointer.Drag | pointer.Release | pointer.Scroll,
 	}
 	oph.Add(ops)
 	if s.flinger.Active() {
@@ -234,7 +234,7 @@ func (s *Scroll) Scroll(cfg unit.Converter, q event.Queue, t time.Time, axis Axi
 			iscroll := int(s.scroll)
 			s.scroll -= float32(iscroll)
 			total += iscroll
-		case pointer.Move:
+		case pointer.Drag:
 			if !s.dragging || s.pid != e.PointerID {
 				continue
 			}

io/pointer/doc.go

@@ -12,7 +12,7 @@ Types
 
 Only events that match a specified list of types are delivered to a handler.
 
-For example, to receive Press, Move, and Release events (but not Enter,
+For example, to receive Press, Drag, and Release events (but not Move, Enter,
 Leave, or Scroll):
 
 	var ops op.Ops
@@ -20,7 +20,7 @@ Leave, or Scroll):
 
 	pointer.InputOp{
 		Tag:   h,
-		Types: pointer.Press | pointer.Move | pointer.Release,
+		Types: pointer.Press | pointer.Drag | pointer.Release,
 	}.Add(ops)
 
 Scroll events are only delivered to the foremost scroll handler.

io/pointer/pointer.go

@@ -92,6 +92,8 @@ const (
 	Release
 	// Move of a pointer.
 	Move
+	// Drag of a pointer.
+	Drag
 	// Pointer enters an area watching for pointer input
 	Enter
 	// Pointer leaves an area watching for pointer input
@@ -180,6 +182,8 @@ func (t Type) String() string {
 		return "Cancel"
 	case Move:
 		return "Move"
+	case Drag:
+		return "Drag"
 	case Enter:
 		return "Enter"
 	case Leave:

io/router/pointer.go

@@ -235,6 +235,10 @@ func (q *pointerQueue) Push(e pointer.Event, events *handlerEvents) {
 	}
 	p := &q.pointers[pidx]
 
+	if e.Type == pointer.Move && p.pressed {
+		e.Type = pointer.Drag
+	}
+
 	q.deliverEnterLeaveEvents(p, events, e)
 	if e.Type == pointer.Release {
 		q.deliverEvent(p, events, e)

io/router/pointer_test.go

@@ -39,7 +39,7 @@ func TestPointerDrag(t *testing.T) {
 			},
 		},
 	)
-	assertEventSequence(t, r.Events(handler), pointer.Cancel, pointer.Enter, pointer.Press, pointer.Leave, pointer.Move)
+	assertEventSequence(t, r.Events(handler), pointer.Cancel, pointer.Enter, pointer.Press, pointer.Leave, pointer.Drag)
 }
 
 func TestPointerMove(t *testing.T) {
@@ -446,7 +446,7 @@ func addPointerHandler(ops *op.Ops, tag event.Tag, area image.Rectangle) {
 	pointer.Rect(area).Add(ops)
 	pointer.InputOp{
 		Tag:   tag,
-		Types: pointer.Press | pointer.Move | pointer.Release | pointer.Enter | pointer.Leave,
+		Types: pointer.Press | pointer.Release | pointer.Move | pointer.Drag | pointer.Enter | pointer.Leave,
 	}.Add(ops)
 }