I am trying to implement a depth map in my 2D game, so that I can use deferred rendering. My problem is, that when sprites are drawn on top of eachother, I cannot get the last z-value stored in that pixel. I am not using the vertex part of the pipeline, instead relying on spritebatch to do layering for me. Is there a way I can easily retireve the previous depth value in the texture? I am using alpha transparency for my sprites, and am not sure if this will cause problems.
This picture is the depth map, where white -> closer to the front. Therefore the white sprite should appear on top of the darker sprite, but it doesn't (the darker sprite is drawn after the lighter one).
Thanks in advance