Also another point is that, if you rely on SVG for rendering you could get away with just the code without thinking too much about the math involved. For instance if I wouldn't have introduced object hierarchy, I wouldn't even have to bother with math at all. SVG can take care of all the transformations, I wouldn't even have to know that matrices exist and that I could use them in svg objects 1-on-1. Dragging an object without a hierarchy would also propably be much easier, all I had to do is to change the translate(x,y) inside of the svg transform attribute.