widget: [API] add child widget argument to Clickable.Layout

To make the semantic relation between the clickable area and its
content clear, it will be important for the clickable clip operation
to cover all of the clickable content.

API change: users of widget.Clickable must now pass the clickable
content to Layout.

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

widget/button.go

@@ -10,6 +10,7 @@ import (
 	"gioui.org/gesture"
 	"gioui.org/io/key"
 	"gioui.org/layout"
+	"gioui.org/op"
 	"gioui.org/op/clip"
 )
 
@@ -90,10 +91,14 @@ func (b *Clickable) History() []Press {
 }
 
 // Layout and update the button state
-func (b *Clickable) Layout(gtx layout.Context) layout.Dimensions {
+func (b *Clickable) Layout(gtx layout.Context, w layout.Widget) layout.Dimensions {
 	b.update(gtx)
-	defer clip.Rect(image.Rectangle{Max: gtx.Constraints.Min}).Push(gtx.Ops).Pop()
+	m := op.Record(gtx.Ops)
+	dims := w(gtx)
+	c := m.Stop()
+	defer clip.Rect(image.Rectangle{Max: dims.Size}).Push(gtx.Ops).Pop()
 	b.click.Add(gtx.Ops)
+	c.Add(gtx.Ops)
 	for len(b.history) > 0 {
 		c := b.history[0]
 		if c.End.IsZero() || gtx.Now.Sub(c.End) < 1*time.Second {
@@ -102,7 +107,7 @@ func (b *Clickable) Layout(gtx layout.Context) layout.Dimensions {
 		n := copy(b.history, b.history[1:])
 		b.history = b.history[:n]
 	}
-	return layout.Dimensions{Size: gtx.Constraints.Min}
+	return dims
 }
 
 // update the button state by processing events.