opengl z-sorting transparency

Question

im rendering png's on simple squares in opengl es 2.0, but when i try and draw something behind an square i have already drawn the transparent area in my top square are rendered the same color as the background.

I am calling these at the start of every render call.

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
glEnable (GL_BLEND); 
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

Answer 1

Your title is essentially the answer to your question!

Generally transparency is done by first rendering all opaque objects in the scene (letting the z-buffer figure out what's visible), then rendering all transparent objects from back to front.