I just found about it, but I already think it might end up in vCalc. Anti Grain Geometry is a open source 2D rendering library with a very liberal license. The feature set looks pretty comprehesive: it supports anti-aliasing, affine transforms, sub-pixel resolution, and alpha blending. Even better, it's designed as a lightweight set of C++ classes, so it shouldn't bloat or slow down vCalc too much. About the only hole is that it doesn't have any kind of built in text rendering; However, even there there are are detailed instructions for using the Windows True Type renderer to generate glpyhs.
All I need now is time...