Add layout components 001-020 with demos and behavior tests

layout/aspectbox.go

@@ -0,0 +1,21 @@
+package layout
+
+import (
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type AspectBoxOptions struct {
+	// W:H is the ratio; zero sides mean 1.
+	W, H int
+}
+
+// AspectBox fills the width and keeps W:H in whole dots.
+func AspectBox(c *ui.Context, o AspectBoxOptions, children func()) *ui.Element {
+	k := pixel.K(c)
+	rw, rh := orDef("AspectBox W", o.W, 1), orDef("AspectBox H", o.H, 1)
+	e := ui.Box(c).FillWidth().Clip()
+	w, check := pixel.WrapWidth(c, e)
+	return e.Height(k.D(w * rh / rw)).Draw(func(p *ui.Painter, r ui.Rect) { check(r) }).Children(children)
+}