最近在玩SceneKit，发现了colorGrading这个属性。医生说Thecontentsvalueforthismaterialpropertymustbea3Dcolorlookuptable,ora2Dtextureimagethatrepresentssuchatablearrangedinahorizontalstrip.并且3D颜色查找表可以从Metal纹理中读取。YoucanprovidedatainthiscubicformatasaMetaltexturewiththetype3Dtexturetype.那么如何设置scnCamera.colorGrading.c