expose event compression

[John Cupitt <john cupitt ng-london org uk>]

Hi all, 

I'm porting an app to gtk2 and I've come across some performance problems caused (I think) by gtk's new expose event compression system.

One of the app's widgets is an image display window, and one of the tools is a panner. Pure left/right and up/down pans are fast and smooth, but diagonal drags are very choppy. I think this is because gtk is sending me the bounding box of all exposes since the last repaint, and for a diagonal drag, the bounding box of a thin strip down the right and a thin strip across the bottom is the entire window. 

Has anyone come across this before, and is there an easy solution?

(in case it matters, it's a drawing area inside viewport inside a scrolled window, and it's being panned by setting new values for the adjustments and calling value_changed on the h and v adjustments separately)

John