ok i have some test-result for you:
first i tried a fresh/clean installed ubuntu 13.04 - got the same weak fps.
- install ubuntu
- apt-get upgrade/update to get latest packages
- switch to x-swat-ppa to get the last stabel graphic drivers
- install the game
after this i switched back and played around a little bit - and figured out the following:
- Setup - "Water Quality" has the main performance impact. Even in the main screen. (max 50FPS with WQ to Refractive/150 with WQ to Simple) - ingame it makes the different from 20 to 60 FPS
- AA doesn't work - no matter what i setup ingame, nothing happens. If i enforce FXAA or "8xMS,24xCS" AA works (via driver-settings) all works fine (see pictures).
- the game seems to be a good cpu-burner - even in main-screen my CPU is at 45% CPU usage.
- the FPS indicator seems to be unreliable. While beeing in main-screen it jumps between 80 till 160 fps. After entering a game it drops down to somewhat near 60 fps. After returning into the main screen, the fps stays at 60fps - nothing important to me (i'am normaly don't watch fps while playing) but could lead to some problem
- some graphic options only adopted after a restart of the game
Running BWK trough wine even the AA works.
Using different Kernels, Compiz or plain xservers don't have any significant and sustained impact on the fps.
I can't escape the feeling that the FPS-Counter is calculated wrong. Event if i run the game at max (with full override through the driver) i'am stuck at 30 FPS. No matter what resolution i choose the fps stays the same. Even launching the game several times (and playing windows several windows) don't bother the FPS really ...
Hopefully this post helps you determine whats going on.