I don't know where to post these things, so I'm putting it here. So here I have a screenshot of an app that reads MIDI control changes in realtime, and uses Cairo which draws into a GDI backbuffer to make a visual output of the changes over time: http://i.imgur.com/klwTa.png
The realtime MIDI input is stored as an array of values, and then Cairo draws them by using straight lines. Note how the lines are a little jagged? That's not because of Cairo, it's due to my MIDI hardware which has a very low update rate. But Cairo actually did a good job, it antialiased the points between the changes and made the lines appear nicer. The result is a hell of a lot better than what GDI can do. Switching from pure win32 drawing to Cairo is a *breeze*. It's really damn simple to use it. I do want to give Cairo's new OpenGL a try though.