[Mesa3d-dev] Stencil-related rendering bug?

[Scott M. <mcm...@ca...>]

I am trying to implement a multipass rendering technique similar
to Mark Kilgard's real-time shadow library, that involves multiple
rendering passes:

1) render the scene with normal lights no stencil
           glEnable(GL_LIGHT0);
           glEnable(GL_LIGHTING);

2) render the front faces of shadow volumes with the following
           glDisable(GL_LIGHTING);
           glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
           glEnable(GL_STENCIL_TEST);
           glDepthMask(GL_FALSE);
           glStencilFunc(GL_ALWAYS, 0, 0);
           glStencilOp(GL_KEEP, GL_KEEP, GL_INCR);

3) render the back faces of the shadow volumes with the following:
           glStencilOp(GL_KEEP, GL_KEEP, GL_DECR);

4) render the original scene with a different color light:
           glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
           glDepthFunc(GL_EQUAL);
           glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
           glStencilFunc(GL_NOTEQUAL, 0, ~0);

           glDisable(GL_LIGHT0);
           glEnable(GL_LIGHT1);
           glEnable(GL_LIGHTING);

With Mesa, everything works except that I get a white
translucent (like screen door transparency) haze where the
shadow volumes are.  This occurs in areas where the stencil
values were incremented and then decremented back to zero
so there should have been no rendering into the color buffer
after the first step.

This does not happen on SGI's or most NT drivers.

Anybody have any ideas?  Should I also report this as a bug?

scott

-- 
Scott McMillan                        mailto:mcm...@ca...
Cambridge Research Associates         http://www.cambridge.com
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