[x3d-public] (FlipY) Texture coordinates for material textures.

[John Carlson]

Be aware that recent email on this subject from Holger Seelig ended up in
spam.



On Sun, Apr 10, 2022 at 1:27 PM GPU Group <gpugroup at gmail.com> wrote:

> I found a flag in shader (sent by uniform) can flip conveniently: if uvs
> are from gltf, node's internal bufferView/Accessor struct flip uv flag set
> (during gltf parsing) and in shader if(flip) uv.y = 1.0 - uv.y.
>
> On Sun, Apr 10, 2022 at 10:12 AM Brutzman, Donald (Don) (CIV) <
> brutzman at nps.edu> wrote:
>
>> Michalis, thanks for noting that problems emerged in prior glTF
>> conversions
>> for the online examples for Web3D.
>>
>> If someone is able to help us correct and update them satisfactorily, that
>> will be welcome.  Likely interesting too since we can then use subversion
>> diff to look at differences.
>>
>> all the best, Don
>> --
>> Don Brutzman  Naval Postgraduate School, Code USW/Br
>> brutzman at nps.edu
>> Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA
>> +1.831.656.2149
>> X3D graphics, virtual worlds, Navy robotics https://
>> faculty.nps.edu/brutzman
>>
>> -----Original Message-----
>> From: x3d-public <x3d-public-bounces at web3d.org> On Behalf Of Michalis
>> Kamburelis
>> Sent: Sunday, April 10, 2022 9:00 AM
>> To: Holger Seelig <holger.seelig at yahoo.de>
>> Cc: X3D <x3d-public at web3d.org>
>> Subject: Re: [x3d-public] (FlipY) Texture coordinates for material
>> textures.
>>
>> The examples on
>> *
>>
>> https://x3dgraphics.com/examples/X3dForAdvancedModeling/GltfSampleModels/ind
>> ex.html
>> <https://x3dgraphics.com/examples/X3dForAdvancedModeling/GltfSampleModels/index.html>
>> are incorrect.
>>
>> You can instead just use
>> https://github.com/KhronosGroup/glTF-Sample-Models/ examples, and convert
>> them to X3D yourself using latest view3dscene with "--no-x3d-extensions"
>> command-line parameter.
>>
>> Explanation:
>>
>> Unfortunately glTF has different treatment of texture coordinates than
>> X3D,
>> assuming that Y=0 is "up" and Y=1 is "bottom of the image". This is
>> consistent with WebGL, but inconsistent with OpenGL, OpenGLES, X3D.
>> (Yes, it sucks that WebGL is inconsistent with OpenGL/OpenGLES in this
>> case.)
>>
>> OTOH: X3D, OpenGL, OpenGLES, all say that Y=0 is "bottom" and Y=1 is "up
>> of
>> the texure image".
>>
>> There are various possible solutions to this:
>>
>> 1. CGE/view3scene by default places "flipVertically=true" in texture
>> nodes,
>> see
>> *
>>
>> https://castle-engine.io/x3d_implementation_texturing_extensions.php#section
>> _flip_vertically
>> But this is non-standard CGE extension.
>>
>> 2.  If you perform conversion using CGE/view3scene->glTF with
>> "--no-x3d-extensions" command-line parameter, than we don't place
>> "flipVertically" in file, instead we process TextureCoordinates contents
>> to
>> flip them.
>>
>> 3. Finally, one can also use TextureTransform as you say.
>>
>> """
>>       textureTransform TextureTransform {
>>         translation 0 -1
>>         scale 1 -1
>>       }
>> """
>>
>> achieves what is necessary.
>>
>> AD 3 is also what i would advise most X3D browsers. (Because AD 2 requires
>> per-vertex processing, which should be avoided in general. AD
>> 1 is CGE specific, and probably most X3D viewers don't care about this
>> extra
>> optimization that "avoids doing TextureTransform at runtime".)
>>
>> The examples on
>>
>> https://x3dgraphics.com/examples/X3dForAdvancedModeling/GltfSampleModels/ind
>> ex.html
>> <https://x3dgraphics.com/examples/X3dForAdvancedModeling/GltfSampleModels/index.html>
>> are just wrong. Someone used CGE/view3dcene without "--no-x3d-extensions"
>> to
>> generate glTF outout, and then removed flipVertically=true, thus making
>> texture coords incorrect. I recall we talked about it with Don,
>> CGE/view3dscene didn't have "--no-x3d-extensions" initially. Looks like
>> noone had time to finalize this properly. The examples should be recreated
>> with "--no-x3d-extensions".
>>
>> Regards,
>> Michalis
>>
>> niedz., 10 kwi 2022 o 17:05 Holger Seelig <holger.seelig at yahoo.de>
>> napisał(a):
>> >
>> > I recently tested the new glTF examples from
>>
>> https://x3dgraphics.com/examples/X3dForAdvancedModeling/GltfSampleModels/ind
>> ex.html
>> <https://x3dgraphics.com/examples/X3dForAdvancedModeling/GltfSampleModels/index.html>
>> with X_ITE alpha version and recognized that the textures
>> coordinated are y-flipped. I also tested View3DScene and it also happens
>> there. I know that glTF does no y-flip with textures  as X3D does, thus a
>> conversion from glTF to X3D should handle this and add a TextureTransform
>> with translation 0 1 and scale 1 -1. This would mean that this
>> TextureTransform must be added to the examples. Is this correct, or are
>> the
>> textures from material nodes somewhere handled specially?
>> >
>> > Best regards,
>> > Holger
>> >
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