In openGL, how can you get items to draw back to front?

Question

By default it seems that objects are drawn front to back. I am drawing a 2-D UI object and would like to create it back to front. For example I could create a white square

Answer 1

As AlanKley pointed out, the way to do this is to disable the depth buffer. The painter's algorithm is really a 2D scan-conversion technique used to render polygons in the correct order when you don't have something like a z-buffer. But you wouldn't apply it to 3D polygons. You'd typically transform and project them (handling intersections with other polygons) and then sort the resulting list of 2D projected polygons by their projected z-coordinate, then draw them in reverse z-order.

I've always thought of the painter's algorithm as an alternate technique for hidden surface removal when you can't (or don't want to) use a z-buffer.