The isClose threshold is switched from 0.000001 pixels to 1 pixel.
As a backup, it checks whether r0 and r1 are finite. It might be
possible to have just the threshold check or just the finiteness check,
but I don't see the harm in having both.
std::abs(w0 - w1) < 0.000001 is removed because it doesn't look like
it's needed. All calculations should run fine even if w0 === w1.
Finally, the point interpolation is tweaked so that at the end of the
flying (when k === 1) it ends up at the exact end point. I didn't see
any bugs related to this, but it seems like a good thing to have
explicitly.
c878f5f7da