(not on GitHub but has API; OSS alternatives like live-trace in Inkscape) If you meant text description of how Vector Magic works (not code): It uses a proprietary sequence of smoothing, corner detection, bezier curve fitting, and color quantization to convert bitmap → scalable vector (SVG/EPS/AI) with far fewer nodes than standard potrace.

(modern, supports color & curved paths) → https://github.com/visioncortex/vtracer

(simple node.js tool) → https://github.com/folays/img2svg

Want me to extract a using VTracer instead?

(older but classic) → https://github.com/autotrace/autotrace