fix texture rotation, <3 @gimhael, fix #35

[illwieckz]

code by @gimhael 🍾 💯 🎉

it works and fix #35:

[illwieckz]

From up to down: scenes known to previously reproduce the bug in parpax map (Unvanquished), train map (Smokin' Guns), metro map (Tremulous).

[illwieckz]

I added the second occurrence of the - 0.5 trick to be consistent.

I quoted some of your words to prevent people to drop or leftover this trick in future optimization/revamp.

[illwieckz]

does anyone has anything to say more?

[cmf028]

LGTM, though it may be more optimal to just bake the translation into the texture transform matricies. That way, you wouldn't sacrifice texture coord precision. It is unlikely to be that much of an issue though.

[illwieckz]

I'm not sure to understand how to do it. So code that works that exists is better than code that may be better but does not exist 😛.

[illwieckz]

@cmf028 I'm merging it. If you have a better idea feel free to submit a PR but I would prefer seeing progress on some other projects you know better than me. 😁