- Expand overly dense & confusing delta assignments.
- Replace bit shift with multiply.
Also link to 'clipped' version of this function
which may be useful to add later.
Existing method was fine for basic polygons but didn't scale well
because its was checking all coordinates for every y-pixel.
Heres an optimized version.
Basic logic remains the same this just maintains an ordered list of intersections,
tracking in-out points, to avoid re-computing every row,
this means sorting is only done once when out of order segments are found,
the segments only need to be re-ordered if they cross each other.
Speedup isn't linear, test with full-screen complex lasso gave 11x speedup.
