streamlines() is implemented by calling stream2() or stream3() to figure out where the lines go. Then it just draws the lines.
You can build the vertex list ahead of time by calling stream2() or stream3() yourself, which will return a cell array of vertex information; streamlines() passed that cell array will just draw the lines.
The question then becomes how stream2() or stream3() are implemented. stream2() turns out to be implemented by calling stream3() .
stream3() starts by doing some interpolation that I do not yet understand the meaning of; then it calls the mex routine stream3c() to do the bulk of the work. The algorithm for stream3() does not appear to be documented.
