public override void OnNodeEnable()
        {
            node = target as NodeMesh;

            meshPreview     = new GUIMeshPreview();
            previewMaterial = AssetDatabase.GetBuiltinExtraResource <Material>("Default-Diffuse.mat");
        }
        public GUIMaterialPreview(PrimitiveType previewPrimitive = PrimitiveType.Sphere)
        {
            objectPreview = new GUIMeshPreview();

            GameObject tmp = GameObject.CreatePrimitive(previewPrimitive);

            previewMesh = tmp.GetComponent <MeshFilter>().sharedMesh;
            GameObject.DestroyImmediate(tmp);
        }