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/button.go

@@ -21,7 +21,6 @@ type Clickable struct {
 	click   gesture.Click
 	history []Press
 
-	keyTag        struct{}
 	requestClicks int
 	focused       bool
 	pressedKey    key.Name
@@ -69,7 +68,7 @@ func (b *Clickable) Pressed() bool {
 
 // Focus requests the input focus for the element.
 func (b *Clickable) Focus(gtx layout.Context) {
-	gtx.Execute(key.FocusCmd{Tag: &b.keyTag})
+	gtx.Execute(key.FocusCmd{Tag: b})
 }
 
 // Focused reports whether b has focus.
@@ -97,7 +96,7 @@ func (b *Clickable) Layout(gtx layout.Context, w layout.Widget) layout.Dimension
 	defer clip.Rect(image.Rectangle{Max: dims.Size}).Push(gtx.Ops).Pop()
 	semantic.EnabledOp(gtx.Enabled()).Add(gtx.Ops)
 	b.click.Add(gtx.Ops)
-	event.InputOp(gtx.Ops, &b.keyTag)
+	event.InputOp(gtx.Ops, b)
 	c.Add(gtx.Ops)
 	return dims
 }
@@ -141,7 +140,7 @@ func (b *Clickable) Update(gtx layout.Context) (Click, bool) {
 			}
 		case gesture.KindPress:
 			if e.Source == pointer.Mouse {
-				gtx.Execute(key.FocusCmd{Tag: &b.keyTag})
+				gtx.Execute(key.FocusCmd{Tag: b})
 			}
 			b.history = append(b.history, Press{
 				Position: e.Position,
@@ -156,7 +155,7 @@ func (b *Clickable) Update(gtx layout.Context) (Click, bool) {
 		filters = append(filters, key.Filter{Name: key.NameReturn}, key.Filter{Name: key.NameSpace})
 	}
 	for {
-		e, ok := gtx.Event(&b.keyTag, filters...)
+		e, ok := gtx.Event(b, filters...)
 		if !ok {
 			break
 		}