Add layout components 001-020 with demos and behavior tests

layout/section.go

@@ -0,0 +1,30 @@
+package layout
+
+import (
+	"strings"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type SectionOptions struct {
+	// Gap is between children; zero means 4.
+	Gap int
+}
+
+// Section titles a group inside a dotted rule.
+func Section(c *ui.Context, title string, o SectionOptions, children func()) *ui.Element {
+	k := pixel.K(c)
+	up := strings.ToUpper(title)
+	return ui.Column(c).Gap(k.D(orDef("Section Gap", o.Gap, 4))).Role(ui.RoleGroup).Label(title).Children(func() {
+		ui.Box(c).FillWidth().Height(k.D(pixel.LineHeight)).Draw(func(p *ui.Painter, r ui.Rect) {
+			g := k.Canvas(p, r)
+			mid, tw := pixel.LineHeight/2, pixel.Measure(up)
+			g.Checker(0, mid, 6, 1, pixel.Faint)
+			g.Text(10, 0, up, pixel.Ink, 1)
+			g.Checker(14+tw, mid, g.W-14-tw, 1, pixel.Faint)
+		})
+		children()
+	})
+}