Disable rim lighting (r_rimLighting) by default

[slipher]

"Rim lighting" purports to make the edges of models stand out. However in my tests, I don't see a very strong correlation between the parts which are lit up and the edges of models. For more geometrically complex models such as the Barricade, it sometimes randomly lightens the model all over the place, which seems bad.

No rim lighting:

With rim lighting:

If the idea is accepted, I will also make a PR for the graphics presets.

[slipher]

I will try an experiment to make it easier to evaluate renderer PRs like this: I will upload the screenshot comparison tool and the screenshot data set I'm using to unvanquished.net for reviewers to browse. Of course the downside is that the thread is not self-contained; I will probably delete the screenshots later.

Navigate using the arrow keys: https://users.unvanquished.net/~slipher/screenshot-compare/1896/viewer.html. Note that fog is disabled since I had several otherwise useful test scenes where the model was obscured by fog.

[illwieckz]

Quote from Chat:

<illwieckz> can bad rim lighting be related to some other bad normal stuff?
<perturbed-mob> Nah it’s just a shitty algorithm
<perturbed-mob> Only works if the model is real smooth and convex
<perturbed-mob> For example it works on granger’s butt but not barricade

[illwieckz]

LGTM.

[illwieckz]

If the feature is not suitable for Unvanquished, we may also remove the option from the GUI.