widget: [API] add content widget parameter to Enum.Layout

To make the semantic relation between the enum widget and its content,
the content must be laid out inside the enum clip rect.

This is an API change. Users of Enum.Layout must provide a content
widget.

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

widget/enum.go

@@ -7,6 +7,7 @@ import (
 
 	"gioui.org/gesture"
 	"gioui.org/layout"
+	"gioui.org/op"
 	"gioui.org/op/clip"
 )
 
@@ -44,8 +45,11 @@ func (e *Enum) Hovered() (string, bool) {
 }
 
 // Layout adds the event handler for key.
-func (e *Enum) Layout(gtx layout.Context, key string) layout.Dimensions {
-	defer clip.Rect(image.Rectangle{Max: gtx.Constraints.Min}).Push(gtx.Ops).Pop()
+func (e *Enum) Layout(gtx layout.Context, key string, content layout.Widget) layout.Dimensions {
+	m := op.Record(gtx.Ops)
+	dims := content(gtx)
+	c := m.Stop()
+	defer clip.Rect(image.Rectangle{Max: dims.Size}).Push(gtx.Ops).Pop()
 
 	if index(e.values, key) == -1 {
 		e.values = append(e.values, key)
@@ -72,6 +76,7 @@ func (e *Enum) Layout(gtx layout.Context, key string) layout.Dimensions {
 		}
 		clk.Add(gtx.Ops)
 	}
+	c.Add(gtx.Ops)
 
-	return layout.Dimensions{Size: gtx.Constraints.Min}
+	return dims
 }