Re: [Celestia-developers] OverlayTexture doesn't work with 3ds or cms objects

[Chris L. <cl...@ww...>]

On Tue, 29 Jul 2003, Grant Hutchison wrote:

> I've been building a set of overlay textures that will drop an IAU latitude
> and longitude grid over all solar system objects with defined prime
> meridians. They're working nicely, except they don't appear when defined for
> irregular bodies. Is that an easy fix, or a hard fix?

Well, it's possible to make it mostly work . . .  The problem is that the 
textures to be used for 3DS meshes are defined withing the 3DS file.  It's 
possible to override them, but you could get some strange results.  Some 
parts of the mesh may not have texture coordinates at all . . .  Or there 
may be more than one texture used in the mesh.  There are a lot of cases 
where there's not a 'right' behavior for overriding the textures specified 
in the 3DS file.  All of the irregular asteroids and moons in the base 
installation have a single texture applied to all triangles in the mesh, 
so there's an obvious, sensible way to render the overlay texture.  It's the 
fact that there's no sensible, /general/ behavior for all 3DS meshes that 
has discouraged me from implementing overlay textures (and night textures as 
well) for anything other than ellipsoids.  Nevertheless, I'm beginning to 
think now that the practical benefits to allowing overlay textures for 
irregular objects should overrule my philosophical objection . . .  I 
should have some free time to work on this next week.

--Chris