What's your Cairo version?
My tests were done with the 1.4.2 release.
The input focus rectangle has been identified as a performance problem some time ago: http://lists.freedesktop.org/archives/cairo/2006-October/008135.html "Another thing we identified at GUADEC is that the dashed stroke for the focus rectangle that GTK+ uses is also a performance problem. This is another case that we should ensure is going through the fast path for whole-pixel regions."
Interesting, the dashed stroke is exactly what's causing problems - thanks for the pointer!
though I *think* it has been adressed since. But if you are running 1.4, that would hint that it still is a problem.
There have been great advances in cairo performance lately, unfortunately this one might have been overlooked. I'll investigate further.
P.S. The performance-list[1] might be a better place for this discussion...[1] http://mail.gnome.org/mailman/listinfo/performance-list
Indeed. Just subscribed to that list. In order to avoid confusing everyone, I'll stay on this list for now, and might open future topics on performance-list (or on the cairo list, if I can make myself useful there).
Nico