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

[Andreas Plesch]

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