void Awake()
{
instance = this;
showColor = new byte[size * size * 4];
material = GetComponent <MeshRenderer>().material;
pencil = new Pencil();
pencil.Init(this, size, size, curve);
pen = new Pen();
pen.Init(this, size, size, curve);
eraser = new Eraser();
eraser.Init(this, size, size, curve);
curBrush = pen;
layerMgr = LayerMgr.GetInstance();
}