Only thing I can think is the 915resolution or i810 drivers has somehow become funky and trying to reinstall them should work similar to below example.
Alternatively there might be something with the game and resintalling the game could fix a dependancy that might be messed up.
Fix any busted dependancy's:
# revdep-rebuild -X
Fix the game if anypart is busted in it's install:
# emerge -p warsaw
# emerge warsaw
using correct names with above.
Note I did not add the -u for update only fresh install like above , it makes a difference.
More than this try the irc / webchat someone there would be able to give a correct / faster fix.