This is a very simple Bezier patch editor based on Z-buffers.
Press Space to switch between points.
(point [0][0] is located at the bottom left corner, point [3][3] is at the top right corner).
After the point is selected, use up, down, left, and right errors and 1 and 2 keys
to increase/decrease the values of Y, X, and Z coordinates respectively.

Here are the source files: