https://github.com/i-saint/RaymarchingOnUnity5/blob/master/Assets/Raymarching/foundation.cginc#L24-L31


https://stackoverflow.com/questions/34532595/how-do-you-write-z-depth-in-a-shader

float compute_depth(float4 clippos)
{
#if defined(SHADER_TARGET_GLSL) || defined(SHADER_API_GLES) || defined(SHADER_API_GLES3)
    return ((clippos.z / clippos.w) + 1.0) * 0.5;
#else
    return clippos.z / clippos.w;
#endif
}