constructor(parent) {
    super(parent)

    this._colorObj = new Color()

    // Properties
    this.size = emptyVec2
    this.borderRadius = emptyVec4
    this.borderWidth = emptyVec4
    this.color = 0
    this.isBorder = false
    this.material = defaultMaterial
  }
A single layer in a UI Block's rendering, e.g. background or border. All layers honor
border radius, which is calculated shader-side for perfectly smooth curves at any scale,
with antialiasing.

Layer meshes are rendered via GPU instancing when possible -- specifically when they share
the same Material instance, layering depth, and shadow behavior.

You shouldn't have to use this directly; UIBlock3DFacade will create these as needed
based on background/border styles.