Update geom.slang

[Hyllian]

• Change some var names to not conflict with other shaders.

[hizzlekizzle]

if you intend on it being tagged onto other shaders, you might want to go ahead and prepend all of the vars with "geom_" or whatever. I did that with the image-adjustment shader after tiring of whackamole.

[Hyllian]

Ok, vars renamed and geom fixed.