This was an excellent graphic demonstrating the z-buffer algorithm. Thanks!
How might you go about resolving ties? ex. if there were two identical copies of a 3d triangle, would you only see one triangle, or parts of both?
In most cases ties aren't an issue, because if there are two pixels with the same x, y, and z values, then that means they occupy the same point in space (which isn't possible most of the time). I suppose there could be some cases where two objects intersect at a pixel, but I think that either choosing only one of the objects to render or mixing the two colors together would both produce equally visible boundaries.
Prof. Ng also mentioned that the ties usually cause a lot of high-frequency signals in the image, which requires more effort t resolve than picking some way to break the ties.