all: use a single tag per widget for event handling

With the introduction of filters, it is now possible to have one tag per
widget by convention. Note that gestures still have their own tags, for
disambiguation.

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

widget/dnd.go

@@ -18,10 +18,9 @@ type Draggable struct {
 	// Type contains the MIME type and matches transfer.SourceOp.
 	Type string
 
-	handle struct{}
-	drag   gesture.Drag
-	click  f32.Point
-	pos    f32.Point
+	drag  gesture.Drag
+	click f32.Point
+	pos   f32.Point
 }
 
 func (d *Draggable) Layout(gtx layout.Context, w, drag layout.Widget) layout.Dimensions {
@@ -32,7 +31,7 @@ func (d *Draggable) Layout(gtx layout.Context, w, drag layout.Widget) layout.Dim
 
 	stack := clip.Rect{Max: dims.Size}.Push(gtx.Ops)
 	d.drag.Add(gtx.Ops)
-	event.InputOp(gtx.Ops, &d.handle)
+	event.InputOp(gtx.Ops, d)
 	stack.Pop()
 
 	if drag != nil && d.drag.Pressed() {
@@ -66,7 +65,7 @@ func (d *Draggable) Update(gtx layout.Context) (mime string, requested bool) {
 	d.pos = pos
 
 	for {
-		e, ok := gtx.Event(&d.handle, transfer.SourceFilter{Type: d.Type})
+		e, ok := gtx.Event(d, transfer.SourceFilter{Type: d.Type})
 		if !ok {
 			break
 		}
@@ -80,7 +79,7 @@ func (d *Draggable) Update(gtx layout.Context) (mime string, requested bool) {
 // Offer the data ready for a drop. Must be called after being Requested.
 // The mime must be one in the requested list.
 func (d *Draggable) Offer(gtx layout.Context, mime string, data io.ReadCloser) {
-	gtx.Execute(transfer.OfferCmd{Tag: &d.handle, Type: mime, Data: data})
+	gtx.Execute(transfer.OfferCmd{Tag: d, Type: mime, Data: data})
 }
 
 // Pos returns the drag position relative to its initial click position.