I want to make a shader about cone sight

276100-tim图片20190505154941.jpg

These images is final result.
I think its working principle is:
1.Get meshes in camera.
2.Input enemy position.
3.Computation of meshes in Conical Visual Field

So,I don’t have enough knowledge about shader.
Can someone help me achieve this shader?
Thank you very much!

Someone help me?