The joy of Xlib

Last week I started writing the next part of the XI2 recipes series, this time detailing button/key/motion events etc. Except that while fixing various inconsistencies I ran into a wall put up by Xlib years ago. In short, Xlib only allows for event sizes of up to 96 bytes (on 32 bit). Previously I've gotten around that by storing pointers to extra memory freed by the client (see XIFreeEventData(3)). However, this not only introduces a potentially huge memory leak in "naive" clients but also makes the actual event structure be quite annoying. Having to dereference into three structs to get the button mask is just not particularly great.

So now I have to rethink how to deal with events on the client side (Xlib only, xcb is not affected, server isn't affected either).

Either way, this means two things:

• the next XI2 tutorial will take another few days


• there will likely be a fairly big API change in how XI2 clients can deal with events.