code: function Overlay(opts) {
    this.type = 'Overlay'
    this.enabled = true
    this.changed = new Signal()
    this.entity = null
    this.dirty = false
    this.x = 0
    this.y = 0
    this.width = 1
    this.height = 1
    this.texture = null
    this.alpha = 1
    this.set(opts)
  }
docs: Overlay position and size if relative to screen size if < 1 or in pixels if > 1