IPhone OpenGL ES anti-aliasing?

Question

Is it possible to enable anti-aliasing for OpenGL ES on the iPhone? I've tried a few different things:
glBlendFunc(GLSRCALPHA, GLONE_MINUS_SRCALPHA);
glEnable(GL_BLEND);
glEnable(GL_SMOOTH);
glEnable(GL_MULTISAMPLE);
and a few others, but none of them work. I'm not exactly an OpenGL heavy, so I wouldn't know if these were even the right kinds of things to enable for anti-aliasing content (it seems like GL_SMOOTH or GL_MULTISAMPLE would work). It seems like the general consensus for OpenGL ES is that anti-aliasing is platform-dependent, but I haven't seen anything which says whether it's possible on the iPhone. I would assume that it would be possible on the iPhone, considering that things drawn with the Quartz CG methods are anti-aliased by default. It looks to me, though, like the only way to do it would be to render into a buffer with two times the width and height, and then scale it down to fit the display. That seems a little bit processor heavy, though, especially on a mobile device. Any input would be greatly appreciated .
Sonny Jim

Answer 1

I've accomplished FSAA(full screen antialiasing) on the iPhone by rendering the same scene multiple times and jittering the perspective matrix.
The technique has been used since the 70s. Details on the technique can be found at http://www.opengl.org/resources/code/samples/advanced/advanced97/notes/node63.ht ml
The iPhone doesn't have an accumulation buffer, but you can still use the same idea by faking an accumulation buffer by copying the contents of the color buffer and blending the passes together yourself. If you depth-sort your scene you can just blend everything together and forget about an accumulation buffer.
There are variations on this technique where you re-render the scene several times in wireframe mode and use the results to antialias just the edges of polygons.
I'm doing a puzzle game that never has a front-facing polygon behind another front-facing polygon, so I don't have to mess around with faking an accumulation buffer or worry about depth sorting. Remember that this will make your fps drop by whatever factor you antialias.