[X3D-Public] [X3D] Invitation: Web3D Town Hall and X3D Interoperability Demonstration; NURBS, TextureTransform problems

[Michalis Kamburelis]

Don Brutzman wrote:
> b.  The fundamental capability for ImageTexture and TextureTransform is
> not consistent for different players.  This discrepancy is pretty astonishing.
> Example scene and documentation:
> https://savage.nps.edu/Savage/Locations/MontereyPeninsulaCollege/PoolMontereyPeninsulaCollege.x3d
> https://savage.nps.edu/Savage/Locations/MontereyPeninsulaCollege/PoolMontereyPeninsulaCollege.html
>
> BS Contact appears to be correct, or at least it matches the TextureTransform values given in the scene.
> Instant Reality, FreeWrl and OctagaVS match each other but looks quite different.
> Xj3D did not render the TextureTransform image.
> SwirlX3D did not render the scene (at least on a Windows 64-bit machine).
> Other players not tested, reports are welcome.
>

view3dscene displays the same result as Instant Reality, FreeWrl and 
OctagaVS. Screenshot from view3dscene attached.

And, as far as I see, it's a bug of BS Contact (and a bug of this X3D 
file, that probably was prepared to match BS Contact result, that 
happens to be incorrect)... Other browsers are correct, IMHO. For 
example, for Shape named TopSidewalk to appear correct (assuming that 
"correct" means you want to see there the "depth..." markers), the 
correct transformation is like this:

   <TextureTransform scale='-1 1' translation='0 -0.121'/>

or

   <!-- equivalent to above, as 1-0.121=0.879 and texture repeats -->
   <TextureTransform scale='-1 1' translation='0 0.879'/>

while the model currently has

   <TextureTransform scale='-1 1' translation='0 -0.899'/>

I don't know why -0.899 works in BS Contact like this... But looking at 
the PNG file, and remembering how the default texture mapping on 
IndexedFaceSet works (see X3D 3.2 spec "13.3.6 IndexedFaceSet" and 
"18.2.3 Texture coordinates"), it follows that:

- By default (without <TextureTransform>) a shape TopSidewalk displays 
the bottom of the texture.

- If you want to see the texture top (where the "depth" markers are), 
you have to shift in Y by a negative value close to 0 (like -0.121) or 
positive value close to 1 but still smaller than 1 (like 0.879 = 1 - 
0.121).

- If you shift by a negative value close to -1 but still larger than -1 
(like the -0.899, used in current model) then you get a piece of texture 
that doesn't contain what you wanted (not the "depth..." markers).

It's a little difficult to explain in words, but hopefully it will make 
sense to you :) I imagine a window that cuts part of the texture, 
"TextureTransform.translation" is like moving this window over the 
texture. Remember that TextureTransform shifts the texture coordinates 
(so it works in the opposite direction if you think about "shifting 
texture image"; this is even noted explicitly in the spec at 
TextureTransform, as "Note that these operations appear reversed when 
viewed on the surface of geometry.").

Regards,
Michalis
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