I need stencil buffer on 3GS to render planar shadow, and polygon offset won\'t work prefect, still has z-fighting problem. So I use stencil buffer to make the shadow correc
Just a note, if you are using GLKView, it is as simple as
view.drawableStencilFormat = GLKViewDrawableStencilFormat8;
where view is: GLKView*
GLKView*