ui/layout: add Align example

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

ui/layout/layout_test.go

@@ -13,28 +13,47 @@ type config struct{}
 
 var cfg = new(config)
 
-var cs = layout.Constraints{
-	Width: layout.Constraint{
-		Max: 100,
-	},
-	Height: layout.Constraint{
-		Max: 100,
-	},
-}
-
 func ExampleInset() {
 	ops := new(ui.Ops)
 
+	// Loose constraints with no minimal size.
+	var cs layout.Constraints
+	cs.Width.Max = 100
+	cs.Height.Max = 100
+
 	// Inset all edges by 10.
 	inset := layout.UniformInset(ui.Dp(10))
 	cs = inset.Begin(cfg, ops, cs)
 	// Lay out a 50x50 sized widget.
 	dims := layoutWidget(50, 50, cs)
+	fmt.Println(dims.Size)
 	dims = inset.End(dims)
 
 	fmt.Println(dims.Size)
 
-	// Output: (70,70)
+	// Output:
+	// (50,50)
+	// (70,70)
+}
+
+func ExampleAlign() {
+	ops := new(ui.Ops)
+
+	cs := layout.RigidConstraints(image.Point{X: 100, Y: 100})
+
+	align := layout.Align{Alignment: layout.Center}
+	cs = align.Begin(ops, cs)
+	// Lay out a 50x50 sized widget.
+	dims := layoutWidget(50, 50, cs)
+	fmt.Println(dims.Size)
+
+	dims = align.End(dims)
+
+	fmt.Println(dims.Size)
+
+	// Output:
+	// (50,50)
+	// (100,100)
 }
 
 func layoutWidget(width, height int, cs layout.Constraints) layout.Dimens {