Help! How to make custom Terrain Shaders in HDRP / Shader Graph?

Hi, I really want to be able to customize the terrain shader. For example, creating effects based on screen position. Or when it occludes the player, stenciling it out.

What is the best way to do this? The shader code files are not easy to edit manually and there is no Terrain shader type for Shader Graph

 

I what to know either