Couldn’t find a quick answer for this via Google search, so here it is: Trine 2 does support full resolution on the new MBP. Not every aspect of the game takes full advantage — mouse cursors and character portraits could be sharper, but nevertheless it’s a sight to behold. No antialiasing required at 2880×1800, and Very High settings look impressive. Verily.
Update 8/17: Frozenbyte released an update v1.161 in the App Store dated 8/16 which has a one line description:
Fixed fullscreen mode for Retina displays.
Update 8/11: Note below that some have had issues getting 2880×1800 to scale properly. If you’re experiencing this problem, first try disabling Automatic Graphics Switching in the Energy Saver section of System Preferences, or using gfxCardStatus to switch to Discrete Only mode as described in the comments.
Update 8/7: Since an official fix is not yet available, I went ahead and downloaded an earlier version of Trine 2 from the interwebs just to see if it would work properly on Mountain Lion, and it does. So if you feel adventurous and really want to play at 2880×1800, you can find version 1.11 on your favorite torrent site and try it out. Hopefully it won’t be long until the version in the App Store is fixed, but at least you can buy a license there and then self-serve to get a fully working version as needed. “Damn it, Jim! I’m a pragmatist, not a lawyer.
Update 8/2: FrozenByte acknowledgement
Mac OS X Mountain Lion in combination with Retina Display will cause a graphics/resolution anomaly in Trine 2. We are working on this. Hopefully we will have some solutions in a few days. Regular Mountain Lion (non-Retina display) should work fine.
Update 7/31: If you have Trine 2 working at 2880×1800, don’t update to 1.16 like I did. It breaks Retina support and opens up improperly scaled. Still runs fine at 1440×900, but Retina is broken. I’ll update when I find a fix.