用于渲染地形的材质类型。可以是内置类型之一，也可以是自定义类型。请参阅 MaterialType。
If you want to use a custom material, set this to Terrain.MaterialType.Custom, then assign a material to Terrain.materialTemplate. Terrain.MaterialType.Custom with Terrain.materialTemplate == null is identical to Terrain.MaterialType.BuiltInLegacyDiffuse.