Re: [Mesa3d-users] Where or where have my polygons gone?

[Brian P. <br...@pr...>]

Stephen J Baker wrote:
> 
> On Wed, 12 Apr 2000, Evan M. Carey wrote:
> 
> > I'm making a 2D map.  Some of the polygons in this map are very very
> > small.  It appears that if a polygon is sufficiently small Mesa throws
> > it out.  I've got sections of my map which are always going to be
> > composed of _lots_ of little polygons and when they are not rendered I
> > end up with a big hole in the map.  If I change my orthographic
> > projection to look closer in at the hole I see that the geometry for the
> > polygons is valid cause they'll show up at close inspection.
> 
> I agree that Mesa should not throw out polygons no matter how
> small - for precisely the reason you say...and the OpenGL specification
> does not permit such a thing to be done.  However, I'm pretty sure I
> heard of such an "optimisation" being added to Mesa (and I protested at
> the time).

There was a problem with FP over/underflow when rendering very small
triangles.  It wasn't an optimization.

Evan, in src/tritemp.h you can try changing the area test for small
triangles and see what happens.  The code in question is:

      if (area * bf < 0 || area * area < .0025)
	 return;

Try replacing the .0025 with a smaller value, or zero.

-Brian