I've just added a brand new GUI example! This time it's a wave player that draws the waveforms of the left and right channels of the wave file, and also draws the playback position as a typical sequencer would do.
It also allows you to change the playback position, just point and click! Here's a screenshot (poor jpeg to save bandwidth): http://i.imgur.com/Wv5Lx.jpg The drawing routine is a little bit expensive, this is due to drawing a lot of lines with cairo in a single call. I'll have to investigate how to make drawing faster.