[x3d-public] Proposal for New Fields for ParticleSystem

[Don Brutzman]

Thanks for contributing this excellent suggestion Holger.  The field
definitions and motivation sound excellent, and the example model looks
great!

Draft specification prose changes follow, patterned after the existing *40.2.3
Color ramps* and *color/colorKey* paragraphs.

   - X3D Architecture draft v4.1, clause 40 Particle systems component, new
   section
   -
   https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4.1-CD/Part01/components/particleSystems.html#ScaleRamps

*40.2.4 Scale ramps*
> A scale ramp is used to specify the scale of particle geometry over time.
> A scale ramp is a variation on the typical use of a coordinate
> interpolator. The key represents relative time values from the start of the
> lifetime of the particle. There should be the same number of scale values
> in the node as there are corresponding key values. If not, the smaller
> number of those two values shall be used. For particles that last longer
> than the last time value, the scale associated with the last time value
> shall be continued for the rest of the lifetime of the particle.


and then

   - X3D Architecture draft v4.1, clause 40 Particle systems component,
   40.4.5 ParticleSystem
   -
   https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4.1-CD/Part01/components/particleSystems.html#ParticleSystem

ParticleSystem : X3DShapeNode {

  SFNode   []       scale             NULL      [X3DCoordinateNode]
  MFFloat  []       scaleKey          []        [0,∞)

The *scale* and *scaleKey* fields specify how to change the size of the
> particle over the lifetime of an individual particle. The *scaleKey* field
> represents the time of the particle in seconds, while the *scale* field
> holds a series of scale values to be used at the given key points in time.
> Each individual SFVec3f scale value in the MFVec3f array may indicate
> uniform or non-uniform scaling. Between key times, scale values are
> interpolated pairwise in a linear fashion, using the same rules defined for
> the CoordinateInterpolator
> <https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4.1-CD/Part01/components/interpolators.html#CoordinateInterpolator>
>  node.


It is worth observing that there are many ways to define a MFVec3f field
holding a *scale *value array.  I think that your choice of Coordinate node
is best for authors because it matches the corresponding design of
ParticleSet *color/colorKey* fields, and also makes animation of the *scale
v*alue array more straightforward.

If all that sounds good, then a second implementation is appropriate.
Improvements and clarifications to the draft X3D 4.1 specification are
always welcome.

Mantis issue 1519 records the ongoing status of this recommended change.

   - Mantis 1519: add ParticleSystem scale interpolation fields to that can
   scale particle sizes over lifetime
   - https://mantis.web3d.org/view.php?id=1519

Have fun with X3D particle systems!  🎊 🎊 🎊

all the best, Don
-- 
X3D Graphics, Maritime Robotics, Distributed Simulation
Relative Motion Consulting  https://RelativeMotion.info


On Wed, Oct 29, 2025 at 10:42 AM Holger Seelig via x3d-public <
x3d-public at web3d.org> wrote:

> The new latest of X_ITE comes now with two new fields for ParticleSystem.
> That are scaleKey and scale fields. They work much like colorKey and color
> fields.
>
> A user asks me for the ability to scale the particles during the time,
> basically to make the particles grow from its creation time and then shrink.
>
> Other 3D engines like Unity have this already for a long time.
>
> With the two new fields it is possible to have a curve and finely adjust
> the size over the time.
>
> New fields will look like this:
>
> inputOutput MFFloat scaleKey [ ]
> inputOutput SFNode scale NULL  [Coordinate]
>
> It will work with all geometry types a ParticleSystem can have, even
> GEOMETRY.
>
> I prepared a very simple example that shows the capabilities of these new
> fields:
>
> https://create3000.github.io/x_ite/playground/?url=https://create3000.github.io/Library/Tests/Components/ParticleSystems/Scales.x3d
>
> Best regards,
> Holger
>
> —
> Holger Seelig
> holger.seelig at yahoo.de
>
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>
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