   Depth Issues
  Right now, I'm working on a map editor for my game engine. It's nearly complete, however, I have noticed some issues with transparent objects. For example, if I draw a sphere with that is 25% opaque, and then draw my scene second. My sphere will be drawn with alpha blending, but it will "clear" the space it was drawn in. Instead of seeing my environment models through the sphere, the sphere will only render the framebuffer's back color. Now, if I change the order of drawing my objects where the transparent sphere is drawn last, I get the desired results. What I am concerned about is that I will not be able to draw my objects in order of transparency in my real-world projects where performance matters. Is there a way to get my sphere to render with true transparency without the pitfall of rendering objects from high-opacity to low-opacity?Here is a link to my incorrect results:http://i882.photobucket.com/albums/ac22/travisTrue08/incorrect_blending.pngHere are the correct results:http://i882.photobucket.com/albums/ac22/travisTrue08/correct_blending.pngI currently have GL_DEPTH_TESTING enabled for both objects when rendering. My depth function is set to glDepthFunc(GL_LEQUAL). The sphere is actually in front of the corridor, so it should be draw like so. Also, that grid is drawn before everything in the scene in both images, so it can be ignored.   
  The only way to do this is to render objects back-to-front, as you discovered.In theory the performance impact of this should not be massive, as you don't need to do the sort each frame, because the likelyhood of your entire scene being different between frame n and frame n+1 is minimal.   ;  Alright, hopefully the extra draw calls necessary to make this work on the computer will also translate well on the iPhone OS platform. State changes are heavy on those devices.   