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