[Linux] - only white screen with music

[Grumbledore]

After starting the game from steam on ubuntu the only thing i see is a white screen with one or two faint darker spots that slowly fade. I can hear music, but can't do anything. I'd really love to play this game, please help!
I use radeon 7870 on proprietary drivers (on default ones the game doesn't open). Anyone has any tips how I could handle this?