custom widgets - advice on where to start?

[James Morris <james jwm-art net>]

Hi,

I need to create some complex widgets for my program. The first of
which is the main widget which will show static rectangles within
which other rectangles appear and disappear at musical rates (think
fast electronic dance music rates). The static rectangles may overlap
each other, but the other rectangles may not.

I'm working in C.

Can anyone recommend a good tutorial for this kind of thing?

I've looked over http://zetcode.com/tutorials/cairographicstutorial/
but it doesn't explain much about creating custom widgets, nor am I
sure if I should use Cairo or not. While I want the display to be
colourful and attractive, I also want lightweight resource
requirements and speed.

Thanks,
James.