How to turn on/off vert. sync. at run time?

You can’t from OpenGL, and I wouldn’t know any other call. It’s a driver issue, so you need to adjust the driver settings by hand.

My driver sucks, I cannot do it by hand. That’s why I asked. But thanks anyway.

under windows u can use the wglWinSwapInterval extension

ups, I apologize!

actually the user might be able to override that extension (hopefully they can)
on my nvidia driver options i have always on, always off, + usually off (or someit) ive never tested to see if they do override the extension.

The way swapIntervals works on ati’s cards that you must have vsync turned on in the control pannel and the game must not specify or specify vsync off (via swapinterval) inorder to avoid poly shear. Any other setting combo results in the faster frame rates with poly shearing.