How does it look?
Try it now!
git clone email@example.com:ondras/primitive.js.git && cd primitive.js
About the algorithm
Most of the ideas are shared with the original app, described at https://github.com/fogleman/primitive/. Rasterization is done via HTML5 , which is very flexible but prohibits reasonable parallelization. Web Worker support is available but not used at all, as it does not currently bring any performance improvement. This might change in the future.
There are no major missing features nor a roadmap. The UI needs some polishing w.r.t. UX. If you think your feature/bugfix/contribution might be worthwhile, please ask before diving into the code. Performance improvements (measurable) are welcome.