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Spin and Scale

Spin controls particle orientation through an ordered rotation stack. Scale controls display or instance scale independently from physical particle radius.

Use Spin when Instances or exported particle orientation must turn. Use Scale when displayed geometry must change size without changing collision radius, fluid spacing, or other radius-based physics. Use Change Radius instead when the physical particle radius must change.

Spin

Ordered Rotation Layers control orientation independently from physical particle radius and linear motion.

Workflow

  1. Add Spin after the Emitters whose orientation should change.
  2. Set Apply to before building the layer stack.
  3. Add one layer and verify it in isolation.
  4. Choose World space for scene-aligned axes or Particle space when the rotation should follow each particle's current local orientation.
  5. Add further layers in the intended evaluation order. Each layer receives the orientation produced before it.
  6. Use Strength before changing the layer's numerical values when the result only needs a partial blend.
  7. Add an Instance post effect to inspect the final orientation on visible geometry.

In Lists, edit Rotation Layers inside the Spin effect. In Nodes, add a Spin Component for each operation. Chain components through Previous, then connect the last one to Spin Components on the Spin effect. The node shows the active layer's main controls; the Inspector contains all settings. You can rearrange the component chain without changing the particle-stream connections.

Layer Stack

Add, remove, reorder, duplicate, enable/disable, and rename layers. Layer Type = Rotation Range, Spin, Spin Acceleration, Rotate, Align to Velocity, Facing, or Roll. Every layer has Blend (Normal, Add, Subtract, Multiply, Difference, Screen, Overlay, Minimum, Maximum) and Strength.

Normal blends toward the layer's requested result. The remaining modes combine rotation components for layered or stylized behavior. Start with Normal unless the interaction between layers is intentional.

Rotation Range

Time Source = On Birth, Particle Age, or Scene Frame; Space = World or Particle. On Birth uses End Rotation and End Variation. Particle Age / Scene Frame use Start Rotation, Start Variation, End Rotation, End Variation, Start Age / Start Frame, End Age / End Frame, Time Variation, Outside Range = Hold, Only In Range, Repeat, or Continue, and an editable Ease curve. All variants include Variation Seed.

Particle Age is measured in simulation seconds, so every particle follows the range from its own birth. Scene Frame synchronizes all particles to the global timeline. On Birth applies End Rotation once and does not animate between the endpoints.

Spin

Timing = Per Frame, Per Second, or On Birth; Space; Spin Amount; Variation; Max Spin Speed except in On Birth mode; and Variation Seed.

Per Frame follows animation frames, while Per Second expresses a time-based angular speed. On Birth is a one-time rotation, not continuous angular motion. A Max Spin Speed component of zero leaves that axis unrestricted.

Spin Acceleration

Timing = Per Frame or Per Second; Space; Acceleration; Variation; Max Spin Speed; Limit Variation; and Variation Seed.

Rotate

Mode = Absolute or Relative, Rotation, Variation, Use Duration / Duration, and Variation Seed.

Align to Velocity

Particle Axis = X, Y, or Z; Rotation Offset; Offset Variation; Variation Seed; and optional Axis Spin with Spin Speed and Spin Variation.

Facing

Facing = Camera, Object, or Screen. Object mode adds Target.

Camera and Screen require an active scene camera. Camera points particles toward the camera position; Screen matches the camera plane for billboard-style orientation.

Roll

Derives rolling speed automatically from particle velocity and radius.

Roll changes orientation only. It does not constrain a particle to a surface or generate collision friction, so use Collision or a surface constraint separately when physical contact is required.

Scale

Controls render/instance geometry scale separately from the physical particle radius.

Workflow

  1. Add Scale after the particle source and before presentation post effects.
  2. Choose Float for uniform size or Vector XYZ for per-axis proportions.
  3. Use Multiply to preserve and scale the incoming geometry scale, or Set to establish an absolute geometry scale.
  4. Add deterministic Variation only after the base size is correct.
  5. Add Growth, Dissolve, or the custom lifetime curve when scale should change over normalized particle lifetime.

  6. Inspect collisions separately. Scale does not enlarge the physical particle radius.

  7. Value Type: Float or Vector XYZ.

  8. Operation: Multiply or Set.
  9. Scale or Scale XYZ: the uniform or per-axis scale value.
  10. Variation: deterministic per-particle variation. When non-zero, Variation Mode = Uniform or Per Axis and Seed are available.

Uniform variation preserves the X/Y/Z proportions. Per Axis variation changes the axes independently. In Lists, use Data Mapping on the Float or Vector scale value. In Nodes, connect a compatible Field to that value's input. The remaining lifetime controls are in the Inspector.

Growth Phase

Enable Growth, Start Scale, Range In, and Variation.

Dissolve Phase

Enable Dissolve, End Scale, Range Out, and Variation.

Custom Scale Over Lifetime

Enable the lifetime curve, set Variation, edit the scale curve, and remap its output with Min and Max.

Growth, Dissolve, and Custom Scale Over Lifetime multiply together. The curve is sampled by normalized particle age, with Min applied to a curve output of 0 and Max to an output of 1. Because these are multipliers, a zero from any enabled lifetime phase reduces the final geometry scale to zero.

Troubleshooting

  • Instances point along the wrong axis: Change Align to Velocity's Particle Axis or add Rotation Offset. Check the Instance post effect's forward-axis setting as a separate presentation transform.
  • Facing produces no result: Set an active scene camera, or assign the Object target.
  • Spin differs with frame rate: Use Per Second when angular motion should be time-based rather than Per Frame.
  • A later Spin layer seems to replace earlier work: Check layer order, Blend, and Strength. Normal intentionally blends toward the later result.
  • Particles look smaller but collide at the old size: Scale is visual. Use Change Radius when physics must change too.
  • Growth and the custom curve make geometry unexpectedly tiny: Their lifetime factors multiply. Test each phase separately.