Add text components 021-040 with demos and behavior tests

text/marquee.go

@@ -0,0 +1,46 @@
+package text
+
+import (
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type MarqueeOptions struct {
+	// Width is the window in dots; zero means 120.
+	Width int
+	Slot  pixel.Slot
+}
+
+type marqueeKey struct{}
+
+type marqueeState struct{ offset, last int }
+
+// Marquee scrolls s a dot a step; hover pauses it.
+func Marquee(c *ui.Context, s string, o MarqueeOptions) *ui.Element {
+	k := pixel.K(c)
+	w := orDef("Marquee Width", o.Width, 120)
+	e := ui.Box(c).Size(k.D(w), k.D(pixel.LineHeight)).Clip().Label(s).Role(ui.RoleText)
+	ms := ui.Local(e, marqueeKey{}, func() marqueeState { return marqueeState{last: -1} })
+	if k.Reduce() || e.Hovered() {
+		ms.last = -1
+	} else {
+		step := k.Tick(c, 20)
+		if ms.last >= 0 {
+			ms.offset += step - ms.last
+		}
+		ms.last = step
+	}
+	period := w + pixel.Measure(s)
+	x := -(ms.offset % period)
+	if k.Reduce() {
+		x = 0
+	}
+	return e.Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		g.Clip(0, 0, w, pixel.LineHeight, func() {
+			g.Text(x, 0, s, o.Slot, 1)
+			g.Text(x+period, 0, s, o.Slot, 1)
+		})
+	})
+}