[x3d-public] STEP interpolation, was Blender > Exporting rig transforms to HAnim?

Mon Jul 17 08:58:46 PDT 2023

Hi Michalis,

On Mon, Jul 17, 2023 at 9:23 AM Michalis Kamburelis
<michalis.kambi at gmail.com> wrote:
>
> > For STEP, I am using the lower value of the interval:
> ...
> > This corresponds to typical x3d interval use, and you may have done the same ?.
>
> Yes, that is indeed what Castle Game Engine / view3dscene is doing too.
>
> If input is between key[n] and key[n+1], then the output of STEP is keyValue[n].

Super. There are also the edge cases:

key[exactly at n] => keyValue[n]
key[< nMin] => keyValue[nMin]
key[> nMax] => keyValue[nMax]

Just to confirm.

> I started converting your testcase (
> https://github.com/andreasplesch/x3dom/blob/step_interpolator/test/regression-suite/test/cases/interpolators/interpolators.html
> ) into standalone X3D file. I noticed a few things special to X3DOM I
> think (aside from lowercase node / field names, which I understand is
> just necessary for HTML5 integration):
>
> - "alphaMode" and "alphaCutoff" specified at "PhysicalMaterial", while
> in X3D 4 they are on "Appearance"

Yes, for historical reasons, because they only apply to PhysicalMaterial.
Appearance has alphaClipThreshold for regular Material in x3dom. There
was some reason why it was not not reused for PhysicalMaterial perhaps
due to shader uniforms or subtle usage differences.

> - "PhysicalMaterial.unlit" boolean, while in X3D 4 we have separate
> node "UnlitMaterial" instead
>
> - baseColorFactor -> it is baseColor in X3D 4
>
> - metallicfactor, roughnessfactor -> just metallic, roughness in X3D 4

Will be easy to rename.

> - diffusefactor, specularfactor, glossinessfactor on PhysicalMaterial
> -> in X3D 4 we follow te glTF standard "metallic-roughness" workflow,
> so there's no no specular / glossinness.

There used to be specular/glossiness for glTF1. We would probably just
keep it as there is also an extension.

> In the end, it was a bit easier to take glTF from
> https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/InterpolationTest/glTF
> and open it in view3dscene, or convert to X3D from view3dscene. But I
> know this is not objective test, sure it was easier this way for me to
> just open in CGE/view3dscene :)

Of course.
x3dom has a different DEF naming convention prefixing with 'glTF_' and
using the node.name when available but I do not think it is necessary
to align.
I noticed the $ character in the DEF names but see
https://www.web3d.org/x3d/content/examples/X3dSceneAuthoringHints.html#NamingConventions:
'Most restrictive and most interoperable guidance regarding choice of
characters in names: can start with letter or underscore character,
but not a number or a colon. Can then include letters, numbers,
hyphen, underscore, or period characters. This interoperability is
important so that files can be converted equivalently between
encodings without validation problems.'

Shapes do not get named

> Quickly scanning view3dscene output, the one CGE/view3dscene-specific
> thing there is "ImageTexture.flipVertically" (we plan to add
> alternative to it, using texture transform for max conformance), the
> rest looks standard X3D 4.

x3dom has boolean flipY which I believe corresponds to an OpenGl flag.
I also noticed the boolean OrientationInterpolator.keyValueQuaternions
. x3dom converts all rotations from axis-angle to Quaternions during
parsing, so this would save a little bit time there but not during the
animation. I would assume Euler angles would be a more common format
to accept from modeling software but that might be one step too far.

Thank you for the nice list which will make it more manageable to work through.

I found another animation example here:
https://github.com/mrdoob/three.js/pull/12907
and uploaded it here:
https://github.com/andreasplesch/Library/blob/gh-pages/Examples/gltf2/interpolation/InterpolationComparison.gltf

Regards, Andreas

>
> Regards,
> Michalis
>
>
> pon., 17 lip 2023 o 07:16 Andreas Plesch <andreasplesch at gmail.com> napisał(a):
> >
> > Hi Michalis,
> >
> > I am putting finishing touches on STEP and CUBICSPLINE interpolation modes.
> >
> > For STEP, I am using the lower value of the interval:
> >
> > key='0 1 2'
> > keyValue='10 11 12'
> >
> > value at key= 0.6 : 10
> > value at key= -0.1 : 10
> > value at key= 2 : 12
> > value at key= 2.1 : 12
> >
> > This corresponds to typical x3d interval use, and you may have done the same ?.
> >
> > I also added CUBICSPLINE to all interpolators except for
> > ColorInterpolator (could be added but seems strange). Doing that I
> > found that for CoordinateInterpolator and NormalInterpolator the
> > layout of keyValues with in and out tangents was most natural this
> > way:
> >
> > keyValue='FrameData1, FrameData2..FrameDataN'
> >
> > where FrameData is the data for a key frame and looks like:
> >
> > [inTangent1, inTangent2 .. inTangentM],
> > [value1, value2 .. valueM],
> > [outTangent1, outTangent2 .. outTangentM]
> >
> > where all entries are Vec3f.
> >
> > The total number of scalar values in keyValue is thus N * 3 * M * 3.
> >
> > I could not test CUBICSPLINE for Coordinate or NormalInterpolator yet
> > since I do not have a test example. Does any scene come to mind ?
> >
> > Perhaps I can augment the Dolphin example with some arbitrary tangents
> > for testing.
> >
> > I also converted the glTF Interpolation Test example to X3D:
> > https://github.com/andreasplesch/x3dom/blob/step_interpolator/test/regression-suite/test/cases/interpolators/interpolators.html
> >
> > It may be useful for testing Position and OrientationInterpolator without glTF.
> >
> > Andreas
> >
> > On Tue, Jun 27, 2023 at 10:34 AM Andreas Plesch <andreasplesch at gmail.com> wrote:
> > >
> > > Hi Michalis,
> > >
> > > Ok, let me work on adding a STEP interpolation mode to interpolators.
> > > Do you want to raise a spec. improvement suggestion ?
> > >
> > > As  a side note, STEP mode is also related to x3d sequencers. A
> > > ScalarInterpolator in STEP mode would be equivalent to a hypothetical
> > > ScalarSequencer, except for the next and previous fields. Hm, perhaps
> > > it makes sense to add next and previous fields to interpolators which
> > > would step through intervals.
> > >
> > > The CUBICSPLINE algorithm for glTF is fairly well documented as far as
> > > I remember. Feel free of course to look up the implementation in
> > > x3dom.
> > >
> > > It is worth noting that the existing SplineInterpolator nodes only
> > > allow for one (central) tangent per key and key value, whereas the
> > > common cubic spline algorithm allows for two tangents (in, and out)
> > > per key and key value. Those mathematically inclined may be able to
> > > show that the x3d algorithm for spline interpolations is equivalent to
> > > the cubic spline algorithm with identical in and out tangents.
> > >
> > > x3dom just mirrors glTF in that inTangent, value, outTangent occur in
> > > triplets in the MF keyValue field. An alternative interface would
> > > introduce keyInTangent and keyOutTangent fields which then would
> > > require sensible default values. Not sure.
> > >
> > > Some thoughts, Andreas
> > >
> > > PS:
> > > A StringSequencer would be useful as a mechanism to store and select
> > > alternative string values for display in Text nodes. I think the
> > > current strategy is to use an IntegerSequencer to select from Shapes
> > > in a Switch. A MFStringSequencer would be more concise and convenient.
> > > Hm, similarly there could be a StringTrigger event utility.
> > >
> > >
> > > On Tue, Jun 27, 2023 at 8:18 AM Michalis Kamburelis
> > > <michalis.kambi at gmail.com> wrote:
> > > >
> > > > Indeed glTF has additional interpolation options, and I think it would
> > > > make sense to add them to X3D.
> > > >
> > > > Looks like X3DOM and view3dscene/Castle Game Engine go in this
> > > > direction already :)
> > > >
> > > > 1. X3DOM has SFString "interpolation" field, default "LINEAR", see
> > > > https://doc.x3dom.org/author/Interpolation/X3DInterpolatorNode.html .
> > > > Andreas above explained how it supports "CUBICSPLINE" option.
> > > >
> > > > 2. view3dscene / Castle Game Engine allow to use "STEP" interpolation
> > > > explicitly.
> > > >
> > > >     For this, we add such field:
> > > >
> > > >     SFString [in,out]   interpolation  "LINEAR" # range: ["LINEAR"|"STEP"]
> > > >
> > > >     .. to all X3DInterpolatorNode descendants (so, all interpolator
> > > > nodes). This seems exactly like X3DOM, we just added "STEP", where
> > > > X3DOM added "CUBICSPLINE". In the end we should probably have all
> > > > ["LINEAR"|"STEP"|"CUBICSPLINE"].
> > > >
> > > > 3. Note that even without this field, with default linear
> > > > interpolation, it was possible to have effectively step interpolation,
> > > > as Andreas mentions. You can just duplicate keys in the middle, like
> > > >
> > > >     key [0 0.33 0.33 0.66 0.66]
> > > >     keyValue [10 10 20 20 30 30]
> > > >     # interpolation "LINEAR"
> > > >
> > > >     This is valid with X3D ("""keys shall be monotonically
> > > > non-decreasing""" according to spec).
> > > >
> > > >     It is equivalent to
> > > >
> > > >     key [0 0.33 0.66]
> > > >     keyValue [10 20 30]
> > > >     interpolation "STEP"
> > > >
> > > >     Using explicit "STEP" is slightly better, as you need 50% less
> > > > memory to store it, less computation (no need to do lerp or detect
> > > > this special case to optimize), and seems just simpler for authors --
> > > > it specifies intention explicitly, which makes sense, also if one
> > > > hopes a round-trip e.g. import to Blender and export to Blender.
> > > >
> > > >     Having such additional interpolation options seems common, glTF
> > > > and Blender too have them (
> > > > https://docs.blender.org/manual/en/latest/editors/graph_editor/fcurves/properties.html#editors-graph-fcurves-settings-interpolation
> > > > ).
> > > >
> > > > 4. Note that view3dscene / Castle Game Engine do not support
> > > > "CUBICSPLINE" interpolation yet, but we plan to.
> > > >
> > > >     For now we support curve interpolation by adding extra
> > > > intermediate keys to the linear interpolation -- so, we have
> > > > needlessly more keys / key values. But this is only a temporary
> > > > solution, we want to support "CUBICSPLINE" properly, like X3DOM.
> > > >
> > > > Regards,
> > > > Michalis
> > > >
> > > > niedz., 25 cze 2023 o 05:33 Andreas Plesch <andreasplesch at gmail.com> napisał(a):
> > > > >
> > > > > > Date: Sat, 24 Jun 2023 10:11:03 -0700
> > > > > > From: Joseph D Williams <joedwil at earthlink.net>
> > > > > > To: Michalis Kamburelis <michalis.kambi at gmail.com>
> > > > > > Cc: GPU Group <gpugroup at gmail.com>,  X3D Graphics public mailing list
> > > > > >         <x3d-public at web3d.org>
> > > > > > Subject: Re: [x3d-public] Blender > Exporting rig transforms to HAnim?
> > > > >
> > > > > > Which shows that yes, you have a list of the key times that just have to be ascending. Default is  linear interpolation between keyvalues. Now new to me, I like the STEP option where value not interpolated but stays the same until next keyvalue change. For that effect, gltf makes it easier. I want that STEP option in x3d! And then there is also the cubic spline with specified tangents. Me want that one too.
> > > > >
> > > > > In order to support glTF x3dom added a CUBICSPLINE with tangents
> > > > > option to interpolators, in the same form as glTF, eg. three values
> > > > > (in tangent, value, out tangent) per key. Parallel to glTF x3dom
> > > > > interpolators have a "interpolation" SFString field which can have
> > > > > "LINEAR" and "CUBICSPLINE" values. I suspect due to glTF support other
> > > > > viewers also already do something like that and could expose such a
> > > > > mode to regular X3D.
> > > > >
> > > > > A STEP option is already elegantly solved by X3D with duplicate keys
> > > > > with different values in series. That allows mixing step wise and
> > > > > linear interpolation in one animation. x3dom just translates glTF STEP
> > > > > to that format which is very straightforward. A dedicated STEP option
> > > > > would be 50% more efficient in storage but I am not sure if this is
> > > > > enough of a benefit to justify duplication of existing functionality.
> > > > > It may not or it may as x3dom already does it internally for glTF. It
> > > > > would be possible to add to x3d as well but perhaps not necessary.
> > > > >
> > > > > Andreas
> > > > >
> > > > > _______________________________________________
> > > > > x3d-public mailing list
> > > > > x3d-public at web3d.org
> > > > > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
> > >
> > >
> > >
> > > --
> > > Andreas Plesch
> > > Waltham, MA 02453
> >
> >
> >
> > --
> > Andreas Plesch
> > Waltham, MA 02453

--
Andreas Plesch
Waltham, MA 02453