Here's why my tdfx v3 doesn't show fog any more[1]: it's the
glPolygonOffset() in the 3D-panel code. And I remembered that
Andy had commented on this problem a while back in the already
mentioned thread ...
| Re: 3d Panel problem
| Date: Fri, 28 Jun 2002 12:47:36 -0700
| From: Andy Ross <[EMAIL PROTECTED]> (NextBus Information Systems)
| [...]
| Curt's intuition was right. These are almost certainly due to
| differences in the implementation of glPolygonOffset() between our
| drivers. I'm using a Geforce 3, which doesn't show this behavior.
| What PolygonOffset does is add a tiny bit to the depth value of
| generated polygons; to lift them off the surface that they're being
| drawn on top of. But the Voodoo cards have thinner depth buffers, and
| I'm using a pretty large offset value to begin with. Let me tune a
| little and see how much smaller I can make it.
| [...]
| One thing you could do is play with
| the value of the POFF_UNITS define in panel.cxx. See if you can find
| the smallest value that prevents z-fighting between instrument layers,
| but doesn't bleed through other geometry. Hopefully there's a number
| that will work for all cards, or at least most cards with an override
| for funny ones.
panel.cxx says:
| // The number of polygon-offset "units" to place between layers. In
| // principle, one is supposed to be enough. In practice, I find that
| // my hardware/driver requires many more.
| #define POFF_UNITS 40
1 would fix my problem. BUT: 40 only breaks the fog in the scenery, while
it works well for the instruments. So I suggest to let POFF_UNITS be 40 but
to reset the PolygonOffset to -1 or zero after having drawn the instruments.
This should also work for all other cards. (Please verify and apply!)
m. :-)
Index: panel.cxx
===================================================================
RCS file: /var/cvs/FlightGear-0.7/FlightGear/src/Cockpit/panel.cxx,v
retrieving revision 1.75
diff -u -3 -p -r1.75 panel.cxx
--- panel.cxx 22 Jul 2002 19:09:42 -0000 1.75
+++ panel.cxx 23 Jul 2002 18:59:07 -0000
@@ -423,6 +423,7 @@ FGPanel::draw()
// restore some original state
glPopAttrib();
+ glPolygonOffset(0, 0);
glDisable(GL_POLYGON_OFFSET_FILL);
}
[1] that's a lie. It =does= still show fog, but the fog is =very= distant
and doesn't match the visibility value. Bringing it nearer by hitting
'Z' a few times "breakes" the tile loader.
Note to users of a recent vim: Have you ever tried something like this? :-)
set listchars=tab:�`,trail:�,extends:>,precedes:<
set list
--
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What hobbyist can put three man-years into programming,
finding all bugs, documenting his product, and distribute it
for free? -- Bill Gates (in the mid-1970s)
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