cairo-1.2.4 and 1.2.6 would support xcb, but require the xcb-util package which is not yet in portage. It seems Bug #93582 is possibly on this task already. Once xcb-util is in portage, the mentioned cairo ebuilds simply need 1. IUSE += xcb 2. DEPEND += xcb? (libxcb xcb-util) 3. econf += $(use_enable xcb)
Hmm, DEPEND possibly needs xcb-proto also and some others, can't say for sure..
All the pieces cairo needs for xcb support should be in the tree. However, cairo 1.2* uses old header paths to the xcb headers and does not build with xcb enabled. It's gotten a lot of attention in recent months, so perhaps consider this a 1.3+ feature.
Thanks Josh. That's where this is going. Into the Gentopia overlay.
In the tree (at least, 1.4.2 seems to have it)