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

Drawing order is hard. There is no easy solution. The painter's alogorithm (sort objects by their distance in relation to your camera's view) is the most straightforward, but as you have discovered, it doesn't solve all cases.

I would suggest a combination of the painter's algroithm and layers. You build layers for specific elements on your program. So you got a background layer, objects layers, special effect layers, and GUI layer.

Use the painter's algorithm on each layer's items. In some special layers (like your GUI layer), don't sort with the painter's algorithm, but by your call order. You call that white square first so it gets drawn first.