Navigation: review r2 fixes

internal/navigation.go

@@ -17,3 +17,15 @@ func Ease(e *ui.Element, d time.Duration, fg ui.Color) *ui.Element {
 	}
 	return e.TextColor(ui.Color{R: ch("mujica.fg.r", fg.R), G: ch("mujica.fg.g", fg.G), B: ch("mujica.fg.b", fg.B), A: ch("mujica.fg.a", fg.A)})
 }
+
+// PopIn fades popup e in over d from the frame it appeared and returns the progress, 0 to 1.
+func PopIn(c *ui.Context, e *ui.Element, d time.Duration) float32 {
+	born := ui.Local(e, "mujica.popin", func() time.Time { return c.Now() })
+	p := float32(1)
+	if t := float32(c.Now().Sub(*born)) / float32(max(d, 1)); d > 0 && t < 1 {
+		p = ui.EaseOut(t)
+		c.AnimationFrame()
+	}
+	e.Opacity(p)
+	return p
+}