I had to spend a couple of hours today rewriting some code after reading about Cython.
I rewrote the C module to a Cython file. It runs at about 1.33 the speed of the C module, but I believe that’s mainly because I’m using tuples all over the place instead of C structs. My guess is that the decrease in speed would become very moderate after optimizing. The new module also got rid of a bug in the C module where objects would disappear when being too far from the viewing plane.
Even if after optimizing there isn’t a huge performance gain, I think the penalty would be well worth it. The code is less than half the length and didn’t take long to write..

Here is an image:

Again, two identical, separated spheres.
There is also some primitive lighting. Note the “banding”… It is caused because the program is rounding floats to ints. Shouldn’t be very tough to fix.