is
Tests if cubic is degenerate.
Cubic with no length or that moves a very short distance is degenerate; it is treated as a point.
Return
true if cubic is degenerate; its length is effectively zero
Parameters
p1
cubic start point
p2
cubic control point 1
p3
cubic control point 2
p4
cubic end point
exact
if true, returns true only if p1, p2, p3, and p4 are equal; if false, returns true if p1, p2, p3, and p4 are equal or nearly equal