[x3d-public] IndexedTriangleSet defaults

[Andreas Plesch]

Apologies, I took a short cut in the hope to get to the question directly
but ended up with producing a surprise.

Not sure how useful the default implementation behaviour for texture
coordinates of IndexedFaceSets is. Although I can see that there are use
cases with overall planar geometries and exactly matching map textures.

Could this implementation behaviour be a candidate for deprecation ? In
contrast, default texture coordinates for the various convenience
geometries (box, plane, sphere, elevationgrid ..) are very useful.

I was coming across this when I looked at three.js and its constructors for
geometry on which in turn aframe's geometric primitives are based. Three.js
does not have IndexedFaceSet but it has IndexedTriangleSet without default
texture coordinates (UV).

It might be good to harmonize where possible.

Since aframe is designed to be very extensible and has concepts similar to
x3d, it may be actually possible to implement a (limited) x3d browser using
aframe as the underlying framework, with x3d nodes and fields corresponding
to aframe components. A thought for another time.

Andreas








On Mon, Apr 11, 2016 at 10:21 AM, Roy Walmsley <roy.walmsley at ntlworld.com>
wrote:

> Hi Andreas,
>
>
>
> Initially I was surprised by your comment below. As you say, the default
> value of the *texCoord* field is NULL for the IndexedTriangleSet node.
> But when I looked at the IndexedFaceSet node, I found that it too has a
> default value of NULL for the *texCoord* field (see
> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/geometry3D.html#IndexedFaceSet).
> So both are in agreement there.
>
>
>
> However, I assume you are referring to the text in the penultimate
> paragraph for the IndexedFaceSet, which commences “If the *texCoord*
> field is NULL, ….”. Here an implementation behaviour is detailed for when
> the default value is NULL. In comparison, the IndexedTriangleSet node has
> no such behaviour defined.
>
>
>
> I don’t know why the two instances are different. It is an interesting
> observation., which is also worthy of a specification comment.
>
>
>
> Regards,
>
>
>
> Roy
>
>
>
> *From:* x3d-public [mailto:x3d-public-bounces at web3d.org] *On Behalf Of *Andreas
> Plesch
> *Sent:* 11 April 2016 14:34
> *To:* X3D Graphics public mailing list
> *Subject:* [x3d-public] IndexedTriangleSet defaults
>
>
>
> For IndexedTriangleSet the default value for texCoord is NULL.
>
>
> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/rendering.html#IndexedTriangleSet
>
> On the other hand the texCoord default value for IndexedFaceSet is a
> reasonable map which tries to fit a texture on the mesh.
>
> Is there a reason for this divergence ?
>
> Andreas
>



-- 
Andreas Plesch
39 Barbara Rd.
Waltham, MA 02453
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