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4722fc09@news.povray.org...
> Just curious.... I want to know what 3d formats besides POV-Ray SDL
> support object instantiation. So far as I'm seeing, .obj does not and yet
> seems like such a basic thing.... Am I wrong? Know of a good place to
> compare formats?
AFAIK, instantiation is not a property of the file format, but a feature of
the renderer.
G.
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Gilles Tran wrote:
> AFAIK, instantiation is not a property of the file format, but a feature of
> the renderer.
True. Although it helps if the file format has some way to express that
the renderer should do this. (E.g., rather than just duplicating the
data twice.)
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Gilles Tran <gitran_nospam_@wanadoo.fr> wrote:
> AFAIK, instantiation is not a property of the file format, but a feature of
> the renderer.
If you tell the renderer "copy this mesh 1000 times over the scene" (but
the mesh data is kept only once in memory), thus getting a nice scene, and
then you want to save this scene into a file, how do you do that if the
file format doesn't support saying "copy this mesh here" commands?
--
- Warp
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> Gilles Tran <gitran_nospam_@wanadoo.fr> wrote:
>> AFAIK, instantiation is not a property of the file format, but a feature of
>> the renderer.
>
> If you tell the renderer "copy this mesh 1000 times over the scene" (but
> the mesh data is kept only once in memory), thus getting a nice scene, and
> then you want to save this scene into a file, how do you do that if the
> file format doesn't support saying "copy this mesh here" commands?
>
Keeping it only once in memory is a feature of the renderer, which
requires such a command on the file format. Having the triangle list
only once in the input file is a feature of the file format. A (quite)
stupid parser could duplicate data in memory even if it's not duplicated
on the file!
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Nicolas Alvarez <nic### [at] gmail isthebestcom> wrote:
> requires such a command on the file format.
That's what I thought.
--
- Warp
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Nicolas Alvarez wrote:
>> Gilles Tran <gitran_nospam_@wanadoo.fr> wrote:
>>> AFAIK, instantiation is not a property of the file format, but a
>>> feature of the renderer.
>>
>> If you tell the renderer "copy this mesh 1000 times over the scene"
>> (but
>> the mesh data is kept only once in memory), thus getting a nice scene,
>> and
>> then you want to save this scene into a file, how do you do that if the
>> file format doesn't support saying "copy this mesh here" commands?
>>
>
> Keeping it only once in memory is a feature of the renderer, which
> requires such a command on the file format. Having the triangle list
> only once in the input file is a feature of the file format. A (quite)
> stupid parser could duplicate data in memory even if it's not duplicated
> on the file!
Basically I like the idea of having the flexibility of being able to
export to a fairly universal format like .obj. But if .obj doesn't
support instantiation, and if my model is (or will be) a collection of
tens if not (perhaps) hundreds of thousands of non-unique meshes (save
the for transformation of each), then man oh man will that be a big
file. I can't imagine most file formats would leave out such a basic
thing.
Anyway unless somebody can answer somewhat definitively about a good
format, it looks like I've got some studying to do. Paul Bourke's page
that Vincent linked to looks useful especially with that handy search
button.
Charles
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Vincent Le Chevalier wrote:
>> Just curious.... I want to know what 3d formats besides POV-Ray SDL
>> support object instantiation. So far as I'm seeing, .obj does not and
>> yet seems like such a basic thing.... Am I wrong? Know of a good
>> place to compare formats?
>>
>
> I have no idea about instanciation specifically, but this page is a good
> start for plenty of data format:
> http://local.wasp.uwa.edu.au/~pbourke/dataformats/
>
> Hope this helps
>
Thanks! This is definitely a good resource to know about.
Charles
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Charles C <"nospam a nospam.com"> wrote:
> Basically I like the idea of having the flexibility of being able to
> export to a fairly universal format like .obj. But if .obj doesn't
> support instantiation, and if my model is (or will be) a collection of
> tens if not (perhaps) hundreds of thousands of non-unique meshes (save
> the for transformation of each), then man oh man will that be a big
> file. I can't imagine most file formats would leave out such a basic
> thing.
A lot of older formats would have been dealing with very simple scenes (for an
example of a format that time has really left behind, look at .3DS). I guess
the use case for a lot of those formats was to hold a single model rather than
a scene. You want a modern interchange format; Collada springs to mind.
Tom
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Tom York wrote:
> A lot of older formats would have been dealing with very simple scenes (for an
> example of a format that time has really left behind, look at .3DS). I guess
> the use case for a lot of those formats was to hold a single model rather than
> a scene. You want a modern interchange format; Collada springs to mind.
Thanks. So far I've been too busy to have a chance to do anything more
than light browsing - I haven't really gone and done my homework fully
yet.
That said, are it seems like back then there'd be even more concerned
about efficiency. E.g. table legs. I guess I should look into scene
formats too. :-) I didn't know there was a difference, but I also notice
.wrl versus .vrml.
Charles
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Tom York wrote:
> Collada springs to mind.
Woohoo! you're right. It's there.
http://www.collada.org/mediawiki/index.php/COLLADA_FAQ
First I saw:
"Transform hierarchy (rotation, translation, shear, scale, matrix)"
which was a good clue that instantiation really be there, and then I saw:
"Instancing"
But why haven't I heard of this Collada before? Is it because it's XML
and the fact that (around here anyway) there seems to be a common
aversion to XML?
Charles
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