The fragment below shows how I’ve setup my stencil test. What I’m trying to do is draw a load of polygons with holes in (using alpha test) and then to draw a further bunch of polygons which may or may not show through the holes. I have had problems with z buffer accurracy when two polygons are really close to each other. Polygon offset hasn’t worked too well because I’m dealing with cylinders (see www.thermoteknix.com for a screenshot!). Thanks for any advice.
If your problem is depth buffer precision, then you should alter your near and far clip planes, since they are the source of the problem. Don’t use a larger view frustum that you absolutely need.
Thanks bob. I’ve tried that solution already. The problem here is that the depth-buffer works on a per-pixel basis, with a limited accuracy whatever my near\far planes are and the alpha-test works on a per-fragment basis (assuming a fragment is larger than a pixel). At places my two cylinders touch geometry-wise but the alpha in the texture might not cover exactly those areas that do touch and so I’m getting z fighting in these places. Someone said stencil might help some time ago and I’ve only just got around to trying it out.