Re: polygon layers

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Marcus Barnes (marcus++at++multigen.com)
Tue, 22 Oct 1996 12:05:10 -0700

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On Oct 22, 7:11am, WILLIAM_MARINELLI++at++ntsc.navy.mil wrote:
> Subject: polygon layers
>
> I notice that if I model coplanar polygons in multigen with the
> following hierarchy ....
>
> g1
> |
> |
> o1
> |___________
> | | | | |
> p1 p2 p3 p4 p5
>
> then I run into the typical z buffer resolution problems that one
> would expect with coplanar when I display the geometry in perfly.

Given what you have modelled, this is correct behavior. Sibling faces have no
relationship to each other wrt coplanar rendering in Performer.

> OTOH if I model the same geometry in with this hierarchy....
>
> g1
> |
> |
> o1
> |
> |
> p1 (ground)
> |
> |
> p2 (airstrip)
> |_____
> | | |
> p3 p4 p5 (stripes)
>
> ...then the problem simply goes away.

[munch]

> Question - is the reason for this because the loader recognizes the
> "parent/daughter" polygons and invokes pfLayer or is it some other
> sort of magic?

The OpenFlight loader translates subfaces (your 2nd example) into pfLayer
geometry. The superface becomes the base layer, and for efficiency, the
subfaces are "unwound" in a breadth first order as decal layers. Because the
subfaces are not unwound depth first (correct way, but would require 1 face per
geoset), sibling subfaces should not overlap each other.

Regards.

--
   __  ___     ____  _ _____        Marcus Barnes, marcus++at++multigen.com
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Next message: Brian Furtaw: "How are these nodes applied to the geometry."
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