I'm thinking of writing a plotting library (similar to e.g. matplotlib), that calls into an existing, established library (such as matplotlib), and I can use javascript, python, C/C++, or shell. I'm plotting datasets, not functions. I need to be able to plot 2D and 3D. Which libraries should I look at?

I guess I care about

• feature set
• how intuitive it is
• how pretty the graphs are
• that it's reasonably fast