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11. One Conditional Action

Delete only older Accent particles with one simple If branch.

Return to the Lists fountain

Use the Lists checkpoint from lesson 9, or switch back to that setup after lesson 10. Save as 11-logic.blend.

Build the condition

  1. In Effects, add Conditional Logic after Change Color in evaluation order.
  2. Set Apply to Group Accent, Iterations 1, and Weight 1.
  3. Add an If branch with the Age condition.
  4. Choose Greater Than, Unit Frames, and Value 36.
  5. Add a Delete action as a child of If. Confirm its indentation.
  6. Replay frames 1–72.
A colored fountain beside an orange group with its oldest particles removed
Frame 72: the Age condition removes older Accent particles while Main keeps its Lifetime.

Older Accent particles disappear

Accent still emits 80 /f and keeps orange color, but particles older than about 36 frames disappear before their ordinary 48-frame Lifetime ends. Main keeps its ordinary Lifetime. The orange population is smaller and carries less old ground-contact geometry.

Age does not mean Blender timeline frame 36: a particle born at frame 50 reaches that age later. Group filtering prevents this rule from deleting Main.

Optional: lower the Age threshold

Use Greater Than 24 frames, replay and compare Accent count. Restore 36. Avoid Spawn while learning this program; spawning can multiply population and needs its own stop rules.

Nodes equivalent

Connect Logic Condition Age to Logic If / Else Condition, and Logic Action Delete to its True program. Connect Program to a group-filtered Logic effect after Change Color. Its particles become the final stream for post effects and Simulation Output.

Troubleshooting

  • Every group disappears: inspect Logic's Group filter.
  • Nothing changes: check Frames unit and the action's parent branch.
  • The rule triggers at one timeline frame: use Age, not Frame.

Reference: Conditional Logic.

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