Re: Rendering both faces with different materials

[Roger H. <rog...@mi...>]

On 10 Oct, 2008, at 03:30, James Walker wrote:

> Some 3D formats allow applying different materials to the front and  
> back
> faces of materials,

Yes but why? Any real world material has thickness even if its only 1  
Angstrom unit so there should be two surfaces with some separation.

But of course that does not help when importing from a format which is  
plain stupid. As long it does not slow down the rest of Quesa then  
your solution sounds fine, I might even use it in my importers.

Best regards,

Roger.



> and I was thinking about how to do that with Quesa.
>   Preferably, I'd want to do it without duplicating the geometry, to
> save memory.  At first I thought that backface culling plus  
> orientation
> styles would do the trick:
>
> Counterclockwise orientation + backfacing-remove means that we define
> the counterclockwise faces to the the front, and cull out the  
> clockwise
> ones.  Clockwise orientation + backfacing-remove means that we define
> the clockwise faces to the the front, and cull out the  
> counterclockwise
> ones.
>
> However, we need to take the vertex normals into account.  If the
> normals were created to face toward the counterclockwise face, then  
> when
> rendering the clockwise face, we need to flip the normals.  Currently,
> Quesa will only flip normals (OpenGL two-sided lighting) when it's not
> doing backface culling.
>
> What I'm considering is adding a new backfacing style, call it
> kQ3BackfacingStyleRemoveFront, which will cull out the front faces
> (where "front" respects the orientation style), but also use two-sided
> lighting.  With this addition, one could render two faces with a
> structure like this:
>
> Group
>   front attribute set
>   backfacing style remove
>   geometry
> Group
>   back attribute set
>   backfacing style remove-front
>   another reference to the same geometry
>
> Does that make sense?
> -- 
>   James W. Walker, Innoventive Software LLC
>   <http://www.frameforge3d.com/>
>
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