JD Fenech wrote:
> So clarify for me:
>
> Can the AC3D exporter actually export double-sided geometry?
Yes it can, you can test it yourself.
Open Blender, Add a mesh Plane, export it as .ac file. You get a one
sided square plane into the .ac file. Blender creates default
doublesided geometry but the .ac exporter converts it to onesided.
Open Blender, Add a mesh Plane, switch to UV Face Select mode, inside
the Texture Face panel hit the Twoside button, export the object as .ac
file. You get a two sided square plane into the .ac file. When .ac
exporter finds faces marked that way it sets them as doublesided.
Compare the two .ac file: same byte size, same faces/vertex count. The
only difference is SURF 0x20 of the twosided polygon instead of the SURF
0x00 of the onesided version.
N.b. the AC3D exporter does not take into account the Mesh Face
Doublesided property!
> From a technical standpoint, it seems to me that double-sided
> essentially doubles the polygon count at various points in the pipeline,
> depending on how they're done (doubles the memory footprint in all
> cases, if the model file actually holds the outside facing faces, also
> doubles the non-volatire storage req'd).
What happens next is of no interest to the modeller while working on the
geometry. It seems that OpenGL doubles the geometry by itself when
encountering doublesided polygons to be rendered, but that does not
bother me as a modeller. It has a big impact in the GPU memory footprint
of course (doublesided polygon are duplicated), and maybe a little in
performance hit (I assume non visible faces have to be considered in the
rendering pipeline by the GPU but I guess they are simply discarded, so
perfomance hit will be almost like nothing), that's why we should avoid
building twosided polygons when not necessary.
> From a practical standpoint, I think I'd rather simply flag a polygon
> as double-sided and let the rendering software deal with it by doubling
> the polygons, etc,
Agreed. See the technique above, it works.
> rather than having to create a duplicate of the
> object I want double-sided and reversing the normals on. While this is
> very simple to do (and I actually tried it before the suggestion was
> made, and it worked), I really disliked having a seperate named object
> that I had to deal with, particularly when trying to do things like
> scaling, rotations, selections, and other single object operations. More
> objects/seperate meshes means more opportunities to screw something up
> or lose track of something important.
> From a modeller's standpoint,
> simplicity is more practical. I'd almost accept doubled model file sizes
> over having more named objects (which if they're duplicates, would
> almost double the size of each modeled object anyway.)
I totally agree. That's a common modeller point of view. The "duplicate
and reverse normals" technique is not only a waste of time, it's total
evil for every mdeller in the world. Of course, that works too, but I
would never suggest something like that to anybody, especially if there
are much better approaches to that. The "duplicate and reverse normals"
method has far too many cons.
> Just my opinion and a RFC (Request For Clarification ;) I know the
> exporter script is actually not FG so it's probably pointless complaint
> (unless someone wants to suggest to the author of the script to allow
> the option of changing some default behaviours)
Well JD, that helps people like us (who like contributing to FG
development in our way) to make things clear about the possible
pipelines to follow while working ... should I say "playing"? :-)
Roberto
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