Bezier Curve
------------

We want to draw the curve P(t), 0 <= t <= 1, such that the curve passes
through p0 and p3.

Curve has tangent 3(p1 - p0) at p0 and 3(p3 - p2) at p3

or P'(0) = 3 (p1 - p0)
        and
   P'(1) = 3 (p3 - p2)

Suppose the curve is P(t) = <x(t), y(t), z(t)>

The constraints for x
  x(0) = P1x     x(1) = P4x
  x'(0) = 3(P1x - P0x)   x'(1) = 3(P3x - P2x)

Note that this has 4 constraints, in looking for a curve x(t) that
satisfies these variables, we need 4 free variables.

x(t) = at^3 + bt^2 + ct + d

x(t) = [t^3 t^2 t^1 1] [a
			b
			c
			d
			]

and x'(t) = [3t^2 2t 1 0] ...

d = p0x
c = 3px1 - 3p0x
b = 3p2x - 6p1x + 3p0x
a = 3p1x - p0x + p3x - 3p2x



[  3p1x  p0x   p3x   3p2x
   3p2x  6p1x  3p0x
   3px1  3p0x
   p0x                     ] == yuck

or

[t^3 t^2 t 1] [ -1  3 -3  1   [ p0x
                 3 -6  3  0     p1x
                -3  3  0  0     p2x
                 1  0  0  0 ]   p3x ]

generally

P->t == same as above with p0->, etc. substituted for p0x