widget/material: use cosntraints for setting pointer hit areas

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

layout/layout.go

@@ -81,6 +81,11 @@ func (c Constraints) Constrain(size image.Point) image.Point {
 	return image.Point{X: c.Width.Constrain(size.X), Y: c.Height.Constrain(size.Y)}
 }
 
+// Min returns the smallest dimensions that satisfy the constraints.
+func (c Constraints) Min() image.Point {
+	return image.Point{X: c.Width.Min, Y: c.Height.Min}
+}
+
 // RigidConstraints returns the constraints that can only be
 // satisfied by the given dimensions.
 func RigidConstraints(size image.Point) Constraints {

widget/material/button.go

@@ -114,7 +114,9 @@ func (b ButtonLayoutStyle) Layout(gtx *layout.Context, button *widget.Button, w
 					w()
 				})
 			})
-			pointer.Rect(image.Rectangle{Max: gtx.Dimensions.Size}).Add(gtx.Ops)
+		}),
+		layout.Expanded(func() {
+			pointer.Rect(image.Rectangle{Max: gtx.Constraints.Min()}).Add(gtx.Ops)
 			button.Layout(gtx)
 		}),
 	)
@@ -146,7 +148,9 @@ func (b IconButtonStyle) Layout(gtx *layout.Context, button *widget.Button) {
 					Size: image.Point{X: size, Y: size},
 				}
 			})
-			pointer.Ellipse(image.Rectangle{Max: gtx.Dimensions.Size}).Add(gtx.Ops)
+		}),
+		layout.Expanded(func() {
+			pointer.Ellipse(image.Rectangle{Max: gtx.Constraints.Min()}).Add(gtx.Ops)
 			button.Layout(gtx)
 		}),
 	)