[x3d-public] 3D graphics, vertex attributes Tangent index and vector

John Carlson yottzumm at gmail.com
Fri May 23 15:37:08 PDT 2025 

I see.  You want to pick a different tangent vector than the gradient
Got it.

Johm

On Fri, May 23, 2025 at 5:29 PM John Carlson <yottzumm at gmail.com> wrote:

> Perhaps a better term would be gradient?  Idk!
>
> John
>
> On Fri, May 23, 2025 at 5:16 PM Michalis Kamburelis <
> michalis.kambi at gmail.com> wrote:
>
>> John: I know, in math, in 3D, you generally speak about "tangent
>> planes" ( https://en.wikipedia.org/wiki/Tangent ).
>>
>> The name "tangent vector" is just a shorthand for "vector lying on a
>> tangent plane". This is a standard for calling this value in the
>> context of bump mapping / normal maps.
>>
>> See e.g. glTF spec with useful definition (
>>
>> https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#introduction-technical-terminology
>> "2.2.3. Technical Terminology" ):
>>
>> """
>> tangent
>>     A unit XYZ vector defining a tangential direction on the surface.
>> """
>>
>> There is also "tangent coordinate space". If you want to get dirty and
>> read about details, search for "tangent normal mapping":
>> https://learnopengl.com/Advanced-Lighting/Normal-Mapping ,
>>
>> https://www.cs.utexas.edu/~fussell/courses/cs384g-spring2016/lectures/normal_mapping_tangent.pdf
>> .
>>
>> Regards,
>> Michalis
>>
>> sob., 24 maj 2025 o 00:05 John Carlson <yottzumm at gmail.com> napisał(a):
>> >
>> > Tangent planes seem more likely than tangent vectors, at least in 3D.
>> >
>> > Just a naming convention.
>> >
>> > John
>> > On Fri, May 23, 2025 at 4:09 PM Michalis Kamburelis <
>> michalis.kambi at gmail.com> wrote:
>> >>
>> >> Don: I don't think that this decision (to never support Tangent node
>> >> in X3D), is correct. I would actually say we should add Tangent to
>> >> X3D.
>> >>
>> >> Let me present a clear argument "why". I copied some of the reasoning
>> >> from mail below to
>> >> https://github.com/michaliskambi/x3d-tests/wiki/Tangent-node-in-X3D ,
>> >> to have a future reference.
>> >>
>> >> 1. Current state: As of now, both X_ITE and Castle Game Engine have
>> >> extensions to define Tangent node.
>> >>
>> >>     So we have invented the "Tangent" node independently in 2
>> >> implementations and, predictably, they are unfortunately
>> >> similar-but-not-exactly the same. Links from this thread, where you
>> >> can notice a difference:
>> >>
>> >>      -
>> https://create3000.github.io/x_ite/components/rendering/tangent/ ,
>> >>      -
>> https://castle-engine.io/x3d_implementation_rendering_extensions.php#section_ext_tangent
>> >>
>> >>     Also glTF format has them. See
>> >>
>> https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#meshes-overview
>> >> , information about "TANGENT".
>> >>
>> >>     ( Holger, if you read this: I think I will change Castle Game
>> >> Engine's Tangent node in the future, to match better both X_ITE and
>> >> glTF, thus we will have matching definitions with X_ITE. Your approach
>> >> is better, Tangent.vector should be 4D. )
>> >>
>> >> 2. Tangents *do not* just repeat the same information as normal
>> >> vectors, DRY principle doesn't apply here. I.e. the tangent vectors
>> >> are *not* a replacement for knowing normal vectors (nor is the other
>> >> way around).
>> >>
>> >>      And just because the model provides normal vectors -- doesn't
>> >> mean that tangent vectors are already precisely 100% determined.
>> >>
>> >>      There are multiple similar algorithms to determine tangent
>> >> vectors. The normal vector alone doesn't yet define the tangent ->
>> >> because in a 3D space, if you have a normal vector -> you still have
>> >> infinite possible values for a vector "orthogonal to normal". So
>> >> tangent vectors are auto-calculated (when not explicitly provided) to
>> >> match the normal vectors, but *also* to match the texture coordinates
>> >> used for normal maps. There are edge-cases when it is just not obvious
>> >> what should be the "perfect tangent" so various implementations
>> >> (MikkTSpace is just one example) can do different things.
>> >>
>> >> 3. Ultimately, the "perfect tangent value" is the one that was used to
>> >> bake the normalmaps. If the authoring tool (like Blender) that you
>> >> used to make normalmaps used a bit different algorithm to calculate
>> >> tangents than your renderer -> then the rendering of normalmaps will
>> >> be slightly "off".
>> >>
>> >>     There's a nice screenshot in
>> >>
>> https://gamedev.stackexchange.com/questions/146855/how-do-you-compute-the-tangent-space-vectors-with-normals-given-in-the-mesh
>> >> , scroll to "There are multiple ways to generate tangent spaces for a
>> >> mesh, and not all of them agree on the result.". The screenshot there
>> >> shows subtle problems that result from having authoring tool and
>> >> renderer calculate a *bit* different tangent vectors.
>> >>
>> >>     So the perfect thing to do, from a renderer, is to *not* calculate
>> >> the tangent vectors, instead take the tangent vectors as provided by
>> >> the authoring tool. That exactly why glTF has tangents, and why X_ITE
>> >> and Castle Game Engine support them too -- we don't just discard
>> >> tangent values from glTF (only to auto-calculate them), we prefer to
>> >> take tangent values recorded in the 3D model, because this makes
>> >> really good rendering.
>> >>
>> >> See
>> https://github.com/michaliskambi/x3d-tests/wiki/Tangent-node-in-X3D
>> >> , which I just created -- it mostly copies what I said above.
>> >>
>> >> I hope this helps. I'll be happy to explain it better on next Web3d
>> >> Friday teleconference, if you're not tired of my talking :) I can show
>> >> how the normalmaps are actually created.
>> >>
>> >> Regards,
>> >> Michalis
>> >>
>> >>
>> >> pt., 23 maj 2025 o 21:03 Brutzman, Donald (Don) (CIV) via x3d-public
>> >> <x3d-public at web3d.org> napisał(a):
>> >> >
>> >> > The X3D group has looked closely at Tangent options in the past and
>> decided not to support it.  Instead we use Normal nodes, as ever.
>> >> >
>> >> > Of geometric note is that they are literally orthogonal and thus
>> either representation can be used to the other.
>> >> >
>> >> > You will not find Tangent node in the X3D specification.
>> >> >
>> >> > X3D 4.1 draft Architecture, Annex Z (informative) Version content
>> >> >
>> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4.1-CD//Part01/versionContent.html
>> >> >
>> >> >
>> >> > Note that the X_ITE documentation specifically notes that support in
>> that application is nonstandard.
>> >> >
>> >> >
>> >> > SFNode [in, out] tangent NULL [Tangent] non-standard]
>> >> >
>> https://create3000.github.io/x_ite/components/geometry3d/indexedfaceset/#fields-tangent
>> >> >
>> >> >
>> >> > There is no issue with codebases adding functionality that might
>> help their capabilities - the X in X3D is extensible, after all - but
>> anyone putting a Tangent definition into an X3D model file is creating
>> nonstandard, invalid, noninteroperable content.
>> >> >
>> >> > Also please be aware that there is a serious design principle behind
>> this decision: DRY.  Thus, a statement I don't expect to repeat: we do not
>> intend to consider Tangent support in future X3D specifications.
>> >> >
>> >> > Wikipedia: Don't repeat yourself
>> >> > https://en.wikipedia.org/wiki/Don't_repeat_yourself
>> >> >
>> >> >
>> >> > And some "dry humor" on that page:
>> >> >
>> >> > The opposing view to DRY is called WET, a backronym commonly taken
>> to stand for write everything twice (alternatively write every time, we
>> enjoy typing or waste everyone's time).
>> >> >
>> >> >
>> >> > Recommendations:
>> >> >
>> >> > if your model data is starting with tangent values (for whatever
>> reason) then convert them to normal vectors, and
>> >> > stick with standard X3D for best results.
>> >> >
>> >> >
>> >> > Have fun with normal X3D!  🙂
>> >> >
>> >> >
>> >> > 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
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > ________________________________
>> >> > From: x3d-public <x3d-public-bounces at web3d.org> on behalf of Joe D
>> Williams via x3d-public <x3d-public at web3d.org>
>> >> > Sent: Sunday, May 18, 2025 5:03 PM
>> >> > To: John Carlson <yottzumm at gmail.com>
>> >> > Cc: Joe D Williams <joedwil at earthlink.net>; Extensible 3D (X3D)
>> Graphics public discussion <x3d-public at web3d.org>
>> >> > Subject: Re: [x3d-public] 3D graphics, vertex attributes Tangent
>> index and vector
>> >> >
>> >> > ok, seems like from what I can study so far,
>> >> >
>> >> > the first use of Tangent vector is authortime production of
>> >> >
>> >> > normalized Normal vector for vertex or face.
>> >> >
>> >> > The  author is looking for relief effects (bumpmapping)
>> >> >
>> >> > that are produced by Tangent vector.
>> >> >
>> >> > This process (MikkTSpace algorithm) would fill Normal vector.
>> >> >
>> >> > This process of generating Normal vector space is called baking.
>> >> >
>> >> >
>> >> >
>> >> > For Level5 runtime,
>> >> >
>> >> > If Normal vector not null then used directly.
>> >> >
>> >> > If Normal vector null, then normals auto generated by creaseAngle
>> >> >
>> >> > If Tangent vector null, then nothing.
>> >> >
>> >> > If Level 5 and Tangent vector not null then possible relief effects
>> >> >
>> >> >  using length of Tangent vector.
>> >> >
>> >> >
>> >> >
>> >> > No "bake" in runtime.
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > For runtime, the generated Normal vector is used and
>> >> >
>> >> > if Tangent vector is not null, for the author to produce relief
>> effects
>> >> >
>> >> > using length of Tangent vector.
>> >> >
>> >> > Is that true?
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > .
>> >> >
>> >> > For runtime
>> >> >
>> >> > -----Original Message-----
>> >> > From: John Carlson <yottzumm at gmail.com>
>> >> > Sent: May 17, 2025 1:15 PM
>> >> > To: Joe D Williams <joedwil at earthlink.net>
>> >> > Cc: Extensible 3D (X3D) Graphics public discussion <
>> x3d-public at web3d.org>
>> >> > Subject: Re: [x3d-public] 3D graphics, vertex attributes Tangent
>> index and vector
>> >> >
>> >> >
>> >> >
>> >> > Please review Michalis’ response on this thread about tangentIndex
>> and tangentPerVertex.  I believe the corresponding normal fields apply.
>> >> >
>> >> > Level 5? That depends on updated standard.
>> >> >
>> >> > On Sat, May 17, 2025 at 2:04 PM Joe D Williams <
>> joedwil at earthlink.net> wrote:
>> >> >
>> >> > * must have tangentIndex (unless tangentIndex same as normalIndex).
>> >> >
>> >> > * If no tangentIndex, coordIndex used?
>> >> >
>> >> > * tangentPerVertex? Can tangent be applied to vertex or face (like
>> normal and color)?
>> >> >
>> >> > * must have tangent vector (may be auto filled).
>> >> >
>> >> > * Level 5 required since level 4 does not have tangent.
>> >> >
>> >> > Thanks,
>> >> >
>> >> > Joe
>> >> >
>> >> >
>> >> >
>> >> > -----Original Message-----
>> >> > From: John Carlson <yottzumm at gmail.com>
>> >> > Sent: May 16, 2025 10:32 PM
>> >> > To: Extensible 3D (X3D) Graphics public discussion <
>> x3d-public at web3d.org>
>> >> > Cc: Joe D Williams <joedwil at earthlink.net>
>> >> > Subject: Re: [x3d-public] 3D graphics, vertex attributes Tangent
>> index and vector
>> >> >
>> >> >
>> >> >
>> >> > Joe,
>> >> >
>> >> > X_ITE IFS:
>> >> >
>> >> >
>> https://create3000.github.io/x_ite/components/geometry3d/indexedfaceset/
>> >> >
>> >> > Summary, only tangent field.
>> >> > John
>> >> >
>> >> > On Fri, May 16, 2025 at 8:59 PM Joe D Williams via x3d-public <
>> x3d-public at web3d.org> wrote:
>> >> >
>> >> > like  for normals, is there a tangentPerVertex true/false where
>> tangent value
>> >> >
>> >> > is associated with vertex or face?
>> >> >
>> >> > If tangentIndex null, is coordIndex used?
>> >> >
>> >> > If Tangent vector null tangents are generated after Normal vector?
>> >> >
>> >> >
>> >> >
>> >> > Thanks,
>> >> >
>> >> > Joe
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > -----Original Message-----
>> >> > From: Extensible 3D (X3D) Graphics public discussion <
>> x3d-public at web3d.org>
>> >> > Sent: May 15, 2025 6:19 AM
>> >> > To: X3D <x3d-public at web3d.org>
>> >> > Cc: Holger Seelig <holger.seelig at yahoo.de>
>> >> > Subject: Re: [x3d-public] 3D graphics, vertex attributes Tangent
>> index and vector
>> >> >
>> >> >
>> >> >
>> >> > There are also glTF tests for tangents:
>> >> >
>> >> > Geometry with tangent node:
>> >> >
>> https://create3000.github.io/x_ite/laboratory/gltf-sample-viewer/?url=https://raw.githubusercontent.com/KhronosGroup/glTF-Sample-Models/master/2.0/NormalTangentMirrorTest/glTF/NormalTangentMirrorTest.gltf
>> >> >
>> >> > Geometry without tangent node (auto generated tangents using
>> MikkTSpace algorithm):
>> >> >
>> https://create3000.github.io/x_ite/laboratory/gltf-sample-viewer/?url=https://raw.githubusercontent.com/KhronosGroup/glTF-Sample-Models/master/2.0/NormalTangentTest/glTF/NormalTangentTest.gltf
>> >> >
>> >> > The reflection in all half spheres should look the same.
>> >> > Turn on IBL (Image Based Lighting).
>> >> >
>> >> > Best regards,
>> >> > Holger
>> >> >
>> >> > --
>> >> > Holger Seelig
>> >> > Leipzig, Germany
>> >> >
>> >> > holger.seelig at yahoo.de
>> >> > https://create3000.github.io/x_ite/
>> >> > https://patreon.com/X_ITE
>> >> >
>> >> >
>> >> > Am 15.05.2025 um 10:35 schrieb Holger Seelig via x3d-public <
>> x3d-public at web3d.org>:
>> >> > All nodes which have a normal field also have a tangent field in
>> X_ITE, because tangents are very important for PhysicalMaterial to render
>> correctly. Because tangents always come in conjunction with normals,
>> normalPerVertex field is also used for tangents.
>> >> >
>> >> > If there is no Tangent node, the MikkTSpace algorithm is used to
>> generate tangent vectors, as need by the glTF specification.
>> >> >
>> >> > If there is a Tangent node and the vector field is empty, results
>> are undefined.
>> >> >
>> >> > Tangent node:
>> >> > https://create3000.github.io/x_ite/components/rendering/tangent/
>> >> >
>> >> > IndexedFaceSet with tangent field:
>> >> >
>> https://create3000.github.io/x_ite/components/geometry3d/indexedfaceset/#fields-tangent
>> >> >
>> >> > Best regards,
>> >> > Holger
>> >> >
>> >> > --
>> >> > Holger Seelig
>> >> > Leipzig, Germany
>> >> >
>> >> > holger.seelig at yahoo.de
>> >> > https://create3000.github.io/x_ite/
>> >> > https://patreon.com/X_ITE
>> >> >
>> >> >
>> >> > Am 15.05.2025 um 10:24 schrieb Michalis Kamburelis <
>> michalis.kambi at gmail.com>:
>> >> > I don't know about Tangent in X_ITE...
>> >> >
>> >> > But in Castle Game Engine we have a similar extension -- Tangent
>> node (
>> https://castle-engine.io/x3d_implementation_rendering_extensions.php ).
>> Looks like we developed it independently from X_ITE :) It certainly makes
>> sense to have a node that carry this information, to have perfect
>> rendering. (Tangents can be auto-calculated, but there are various details
>> in the auto-calculation algorithm that various renderers may do a bit
>> differently. When the 3D author used "baking" to make a normalmap texture,
>> it's better to use exact same tangents as known by the 3D authoring tool.)
>> >> >
>> >> > At least for Castle Game Engine, the answer is: if the Tangent node
>> is not present, but we need tangents (e.g. for bump mapping), then the
>> tangent vectors are calculated to match the normal vectors. So there's no
>> additional tangentPerVertex or tangentIndex, they would not make sense. By
>> knowing the normal vectors, by know all we need to generate reasonable
>> tangent vectors.
>> >> >
>> >> > See
>> https://castle-engine.io/x3d_implementation_rendering_extensions.php for
>> more details.
>> >> >
>> >> > Regards,
>> >> > Michalis
>> >> >
>> >> > czw., 15 maj 2025 o 07:43 John Carlson via x3d-public <
>> x3d-public at web3d.org> napisał(a):
>> >> >
>> >> > Note, it’s Tangent vector=… not Tangent point=…
>> >> >
>> >> > John
>> >> >
>> >> > On Thu, May 15, 2025 at 12:38 AM John Carlson <yottzumm at gmail.com>
>> wrote:
>> >> >
>> >> > I’d ask Holger, cc’d
>> >> >
>> >> > I’ve not used Tangent, myself.
>> >> >
>> >> > X_ITE Supports up to Level 4, so I guess you’re proposing a new
>> level 5 for the Geometry 3D component?
>> >> >
>> >> > Look at X_ITE IFS:
>> >> >
>> >> > <IMG_0516.png>
>> >> >
>> >> > Maybe check Holger’s create3000 Library for examples?
>> >> >
>> >> > To retrieve examples, last time I tried:
>> >> >
>> >> > git clone https://github.com/create3000/Library
>> >> > Online at:
>> >> >
>> >> > https://github.com/create3000/Library
>> >> > Let’s get v2 Joe Kick out the door, check v2 finger joints, and make
>> sure all joints have converted to v2.
>> >> >
>> >> > John
>> >> >
>> >> > On Wed, May 14, 2025 at 10:45 PM Joe D Williams <
>> joedwil at earthlink.net> wrote:
>> >> >
>> >> >
>> >> >
>> >> > Main questions, in IFS Level5:
>> >> > Is a default tangent generated if Tangent point="" field empty?
>> >> > tangentPerVertex? assigned to vertex or face?
>> >> > tangentIndex? If no tangentIndex is coordIndex used?
>> >> >
>> >> >
>> >> >
>> >> > Thanks,
>> >> > Joe
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > -----Original Message-----
>> >> > From: John Carlson <yottzumm at gmail.com>
>> >> > Sent: May 14, 2025 3:00 PM
>> >> > To: Extensible 3D (X3D) Graphics public discussion <
>> x3d-public at web3d.org>
>> >> > Cc: Joe D Williams <joedwil at earthlink.net>
>> >> > Subject: Re: [x3d-public] 3D graphics, vertex attributes
>> >> >
>> >> >
>> >> >
>> >> > Joe,
>> >> >
>> >> > X_ITE has a tangent node:
>> >> >
>> >> > Tangent | X_ITE X3D Browser
>> >> >
>> >> > Enjoy!
>> >> >
>> >> > John
>> >> >
>> >> > On Wed, May 14, 2025 at 4:46 PM Joe D Williams via x3d-public <
>> x3d-public at web3d.org> wrote:
>> >> >
>> >> > From this:
>> >> >
>> >> >
>> https://docs.google.com/document/d/1hCetnGIkut_dyt4mwkDSTNiLTbrVg1jLo_EArE74DRg/edit?tab=t.0
>> >> >
>> >> >
>> >> > In 3D graphics, vertex attributes define per-vertex data necessary
>> >> > for rendering, animation, shading, and so on.
>> >> > These attributes include geometric properties such as
>> >> > position, normal, tangents, texture mapping information (UV
>> coordinates),
>> >> > shading data (vertex colors), and
>> >> > deformation information (skinning weights and blend shapes).
>> >> >
>> >> >
>> >> > In this discussion of vertex attributes, the only one I don't recall
>> >> > seeing in X3D is tangent?
>> >> >
>> >> > Associated with this work:
>> >> >
>> https://docs.google.com/spreadsheets/d/18d1qy4jx-d_kLsam-JQAzig23w7dTau0Moe7M32lVvk/edit?gid=0#gid=0
>> >> >
>> >> >
>> >> > Thanks,
>> >> > Joe
>> >> >
>> >> >
>> >> > _______________________________________________
>> >> > x3d-public mailing list
>> >> > x3d-public at web3d.org
>> >> > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>> >> >
>> >> >
>> >> >
>> >> > _______________________________________________
>> >> > x3d-public mailing list
>> >> > x3d-public at web3d.org
>> >> > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>> >> >
>> >> > _______________________________________________
>> >> > x3d-public mailing list
>> >> > x3d-public at web3d.org
>> >> > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>> >> >
>> >> >
>> >> >
>> >> > _______________________________________________
>> >> > x3d-public mailing list
>> >> > x3d-public at web3d.org
>> >> > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > _______________________________________________
>> >> > x3d-public mailing list
>> >> > x3d-public at web3d.org
>> >> > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>>
>
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