public static RendererMaterialSwap Swap(Renderer renderer, Material material, float dur)
{
if (renderer == null) throw new System.ArgumentNullException("renderer");
if (material == null) throw new System.ArgumentNullException("material");
var swap = renderer.AddOrGetComponent<RendererMaterialSwap>();
swap._renderer = renderer;
swap.StartSwap(material, dur);
return swap;
}