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/material/checkbox.go

@@ -3,10 +3,7 @@
 package material
 
 import (
-	"image"
-
 	"gioui.org/layout"
-	"gioui.org/op/clip"
 	"gioui.org/unit"
 	"gioui.org/widget"
 )
@@ -34,9 +31,7 @@ func CheckBox(th *Theme, checkBox *widget.Bool, label string) CheckBoxStyle {
 
 // Layout updates the checkBox and displays it.
 func (c CheckBoxStyle) Layout(gtx layout.Context) layout.Dimensions {
-	dims := c.layout(gtx, c.CheckBox.Value, c.CheckBox.Hovered())
-	defer clip.Rect(image.Rectangle{Max: dims.Size}).Push(gtx.Ops).Pop()
-	gtx.Constraints.Min = dims.Size
-	c.CheckBox.Layout(gtx)
-	return dims
+	return c.CheckBox.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
+		return c.layout(gtx, c.CheckBox.Value, c.CheckBox.Hovered())
+	})
 }