BoidsPlayground
Good things take a moment — worth the wait!

Watch how a school of fish organizes itself

Click "Radius spheres & distances" (in the panel at right) to see under the hood. Then play with the sliders to see how the schooling changes — with visual cues showing what's going on.

Click the ? button (upper right of the panel) for short descriptions of every slider.

The three rules

Every fish follows just three simple rules — and the schooling emerges on its own:

  • Separation — don't crowd your neighbors
  • Alignment — swim the way your neighbors swim
  • Cohesion — steer toward the group center

Try this

  • Crank Separation strength to max — watch them scatter
  • Drop Alignment strength to zero — the school falls apart
  • Max out Cohesion strength — they cluster into a tight ball

What the spheres show

With "Radius spheres & distances" checked, each sphere shows a fish's awareness range for the selected rule — that's all it can "see." The colored lines show which fish are listening to each other. Toggle between Separation, Alignment, and Cohesion spheres to see how each rule operates.

For a deeper dive, the About Boids page explains the algorithm in detail.

Boids Parameters
Sim speed 1.0 Speeds up the whole simulation uniformly. Parameter effects (schooling, separation, etc.) stay proportional — they just happen faster.
School Behavior ▼
Separation radius 7.5 Fish closer than this push each other away. Raise it and fish give each other a wider berth.
Alignment radius 6.5 Fish within this distance try to match each other's heading. Larger = each fish listens to more of the school.
Cohesion radius 10.0 Fish within this distance steer toward the group center. A large value pulls distant stragglers back.
Separation strength 5.0 How hard fish push away from close neighbors. Higher = more spread out.
Alignment strength 1.5 How strongly fish match their neighbors' direction. High = tight, synchronized school.
Cohesion strength 1.2 How hard fish pull toward the group center. Raise to cluster more tightly.
Turn & Damping ▼
Tang turn rate 4.0 How quickly blue tangs rotate toward their target heading. Higher = snappier turns.
Triggerfish turn rate 5.0 How quickly the triggerfish rotates along its path. Higher = hugs the curve more tightly.
Vertical damping 0.20 Reduces vertical acceleration. Lower = fish bob up and down more freely.
Distance damping 0.50 Reduces depth acceleration. Lower = fish scatter more toward/away from the camera.
Separation Too close — pushing each other apart Alignment Close enough to match each other's direction Cohesion Drifting apart — being pulled back in Triggerfish Tang is scared away by the triggerfish Spheres Each sphere shows a tang's radius for the selected rule below How close is too close — pair with the separation radius slider Heading-matching zone — the yellow arrow shows the school's average direction Group-pull zone — fish steer toward the center of neighbors in this radius