3d74f4c1@news.povray.org...
> I was more thinking of clear lines, such as lines in clothes, and lines
> separating clothes texture and skin texture. Making those match up
> completely continuously would seem difficult to me.

Well it's easy, since clothes are by definition made of 2D flat material cut
and folded at the right places... uv maps for clothes look just like regular
cloth patterns.
In hi-res models, cloths and skins are different objects, so there's no
problem here either. Really, uv mapping is not such a complex problem (to be
frank I didn't believe it until I got my hands on obj2pov in 1998).

> I can imagine. One thing I can't understand is the limitation in POV-Ray
> that UV vectors have to be UV (2d) vectors instead of 3d vectors. The
> textures are 3d anyway, even image_maps, and one could easily take
> advantage of 3d procedural textures if 3d coordinates were allowed in UV
> maps. (I know that UV means 2d, but what things are *called* isn't
> really the issue here. I see no practical reason for the limitation.)

The fact is that UV mapping is a surprisingly robust and efficient
technology. The mesh2 format is just an implementation of it that works fine
and is 100% consistent with industry formats like OBJ or 3DS.
Regular procedural pigments works fine with too uv mapping. They're just
taken in the <0,0,0>, <1,1,0> space and are very easy to control. Some
normal{} statements, for instance, are typically difficult to set up on
classic CSG (quilted normal on a curved object anyone ?) but are totally
natural to uvmapping.  Just try it :-)

Btw, what effects do you think that could be done only with 3d UV mapping
(just curious) ?

G.

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Gilles Tran wrote:
> Well it's easy, since clothes are by definition
> made of 2D flat material cut and folded at the
> right places...

Hmm. Maybe so...

> The fact is that UV mapping is a surprisingly
> robust and efficient technology. The mesh2 format
> is just an implementation of it that works fine
> and is 100% consistent with industry formats like
> OBJ or 3DS.

I fully agree. I just don't see the reason for the limitation when it
has some disadvantages and no advantages. Specifying 3d vectors would be
optional, as 2d vectors would be perceived as 3d vectors with the third
component being 0.

> Regular procedural pigments works fine with too
> uv mapping.

Yes, but is confined to the x-y plane.

> (quilted normal on a curved object anyone ?)
> but are totally natural to uvmapping.  Just try it :-)

Hey, I'm not talking about a replacement! Regular UV mapping is indeed
very useful. :)

> Btw, what effects do you think that could be done
> only with 3d UV mapping (just curious) ?

Well, here's a bad but illustrative example. Say you have a statue made
of marble. A 3d solid procedural texture is perfect for this purpose
(because in reality marble is solid) and much easier to use than being
forced to use a UV map on the x-y plane (because in reality the marble
pattern isn't wrapped around the object). Then suppose you want the
statue to come to life and move and of course still have the texture
stick to the surface. You need UV mapping for that, but it would be nice
if you could just use 3d coordinates for the UV map so you wouldn't have
to find a way to wrap the x-y plane around the object and make it look
solid.

Actually, make it a wooden figure that comes to life. Isn't it very hard
to "simulate" 3d solid texturing when using 2d UV maps?

Basically, think of it as 3d solid mapping that stick to the surface
when it moves. Most useful for animations of course.

There are also other uses, but this was the first that came to my mind.

Rune
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3d751704@news.povray.org...
> Basically, think of it as 3d solid mapping that stick to the surface
> when it moves. Most useful for animations of course.

OK I understand better what you mean.
I suppose that for the usual mesh-based modellers and renderers, it's not
really a problem of uv-mapping, but a question of defining the right map by
plotting the right pigment at the right place. I guess that  the various 3D
painting software have a feature that lets the user define a 3D procedural
texture, run it through a 3D object and then create the map accordingly.
Perhaps that's the way it's solved usually, or perhaps it's considered as a
minor issue to be solved by usual 2D mapping techniques... I don't know so I
can't elaborate on this.
Now in the case of procedural mapping done in POV-Ray, such 3D uv coordinate
system would make actually sense for animations like your animated statue
scenario, once a POV-Ray mesh animation feature exists that can take full
advantage of it, that is... Seems a very long shot to me, but well, why not.


G.

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