This is a basic Ray-Marcher written in GLSL. Currently, if you set it up the gl_FragColor will output:

vec4(normal.x, normal.y, normal.z, depth)

If the ray does not hit anything, the gl_FragColor will output:

vec4(0.0)

I have not tested it, but I am very certain it would work when given an environment to work with.

It requires the Resolution, vec2(x, y) the Camera FOV, float fov the Camera Position, vec3(x, y, z) and the Rotation Matrix. The first vec3 of the rotation matrix matches the right and left sides of the screen. The second vec3 of the rotation matrix matches the top and bottom of the screen. The third vec3 of the rotation matrix matches the forward and backwards direction of the screen. For example, you could use:

mat3(1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 1.0)

This matrix will result in the right side of the screen being +X, the top side of the screen being +Y, and the forward direction of the screen +Z.