[x3d-public] unmatched xxxTextureMapping

[Michalis Kamburelis]

This case is clarified in the text you link to:

"""
If the xxxTextureMapping field is not empty, it should refer to a
corresponding X3DSingleTextureCoordinateNode node on a list of texture
coordinates. [...] If no corresponding X3DSingleTextureCoordinateNode
is found on this list, the X3D browser should determine texture
coordinates as if xxxTextureMapping would be empty (see below). [...]

If the xxxTextureMapping field is empty, then the first item on a list
of texture coordinates is used (regardless of the mapping value). Only
if no such texture coordinate exists (the list is empty), then then
default texture coordinates for the specific geometry node are used.
"""

IOW, in simple terms: if xxxTextureMapping does not match any
TextureCoordinate, then use the first TextureCoordinate. With the
"first TextureCoordinate" meaning, in the order of preference,
1. the first in MultiTextureCoordinate list,
2. or just literally the only TextureCoordinate if no
MultiTextureCoordinate was used,
3. or it can mean a fallback to default texture coord.

Regards,
Michalis

pt., 21 lut 2025 o 19:31 Andreas Plesch via x3d-public
<x3d-public at web3d.org> napisał(a):
>
> As https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4.1-CD/Part01/components/shape.html#TextureMappingCoordinate
>
> and co. explains the xxxTextureMapping field can be used to have multiple sets/channels of TextureCoordinates for the same Shape, for different types of Textures.
>
> There is one case which is not covered, presumably because it typically would indicate a mistake or oversight by the author. What should a browser implementation do if a material has a (non-default) xxxTextureMapping which does not match any of the provided TextureCoordinates for the Shape ?
>
> Possibilities are fall-back to default texture coordinates, fall-back to the first provided mapping, fall-back to constant uv 0,0 to indicate visually a problem, or undefined behaviour.
>
> Undefined behaviour might be ok but it is then worth pointing out in the spec.
>
> Thanks, -Andreas
>
> --
> Andreas Plesch
> Waltham, MA 02453
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