Hi meyer
Althought drawing the pie slices is much easier than drawing the lines of the sparkline, the complexity of that kind of chart resides in the placement of labels.
When the labels are not to wide it's fairly simple (and I'm already so far).

But if the size of the label increases it gets tricky to render something appealing.

Note that both screenshot above are rendered with the same available space.
I can think of several (like: a lot) ways to deal with that but I'd rather have a discussion about the pros and cons before continuing, too far, in one direction.
Hi meyer
Althought drawing the pie slices is much easier than drawing the lines of the sparkline, the complexity of that kind of chart resides in the placement of labels.
When the labels are not to wide it's fairly simple (and I'm already so far).

But if the size of the label increases it gets tricky to render something appealing.

Note that both screenshot above are rendered with the same available space.
I can think of several (like: a lot) ways to deal with that but I'd rather have a discussion about the pros and cons before continuing, too far, in one direction.