In the natrual environment, moss or snow appear on the top of the stones. This requires a shader to blend two or more textures in a specific way. Such shader can save great effort of environment artists. This matrial can apply to any shape and topling texture can be changed acoording to different senarios.

The main function used to blend colors is the lerp() function. In order to make moss generated on the top of each breakout part, we need to change the z channel of normal map into the world coordinate system.