First, all the lines and rings in the input geometry are identified in pink.
Second, arc intersections are found in yellow. (The intersecting arcs can be seen in blue and red if you zoom in.)
Third, rings are rotated and cut so that each arc can represented be uniquely. The red arc is the segment after the cut, and the blue arc is the segment before; rotated rings are in pink.
Lastly, the arcs are deduped so that each unique arc is only represented once. The first time an arc is seen, it is shown in pink, while duplicate arcs are shown in yellow.
Pressing a key will interrupt the animation. Use the arrow keys to step forwards and backwards through the construction process. In the console,
current refers to the current step.