heh, im currently working on an svg pathstring to canvs2d command compiler [1] and had to dive into this topic last week, including converting arc commands from centerpoint parameterization to endpoint parameterization [2]

[1] https://github.com/leeoniya/uMarks (WIP!)

[2] https://www.w3.org/TR/SVG/implnote.html#ArcConversionCenterT...