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Physics

Set up physics simulation with collision layers and materials.

21 min read Intermediate Updated 2026-07-01 v2.0 ~71 min to complete

Introduction

Physics simulation makes your game world feel real. This guide covers physics engine setup, collision layers, physics materials, and performance tuning.

Guide 10 of 25

This is part of the Intermediate Guides collection. Category: Physics. Estimated completion: 71 minutes. Difficulty: Intermediate.

Screenshot

Step-by-Step Guide

Configure physics settings

In Project Settings > Physics, set gravity (-9.81 Y), fixed timestep (0.0167 for 60Hz), and solver iterations (4-8).

Set up collision layers

Define layers: Player, Enemy, Environment, Projectile, Trigger. Configure interaction matrix.

Create physics materials

Make materials: ice (friction 0.1, bounce 0), rubber (friction 0.8, bounce 0.9), metal (friction 0.3, bounce 0.2).

Add colliders to objects

Assign shapes: box for walls, sphere for balls, capsule for characters, mesh for complex static geometry.

Configure rigidbodies

For dynamic objects, set mass, drag, angular drag, and gravity. Use kinematic for player-controlled objects.

Tune solver iterations

Increase (8-16) for stacked objects or complex joints. Decrease (2-4) for simple scenes to save CPU.

FluxScript Example

Here is a complete FluxScript implementation for this guide:

Physics — FluxScript

on start {
  physics.setGravity(0, -9.81, 0)
  physics.setFixedTimestep(0.0167)
  physics.setSolverIterations(6)
  physics.setLayer("Player", 0)
  physics.setLayer("Enemy", 1)
  physics.setLayer("Environment", 2)
  physics.setLayer("Projectile", 3)
  physics.setCollision(0, 1, true)
  physics.setCollision(0, 2, true)
  physics.setCollision(3, 1, true)
  physics.setCollision(0, 3, false)
  ice = physics.createMaterial("ice", { friction: 0.1, bounce: 0.0 })
  rubber = physics.createMaterial("rubber", { friction: 0.8, bounce: 0.9 })
  scene.find("IceFloor").setPhysicsMaterial(ice)
  scene.find("RubberBall").setPhysicsMaterial(rubber)
}

Node Graph Example

Prefer visual programming? Here is the equivalent Node Graph:

Physics — Node Graph

[On Start] --> [Set Gravity + Timestep + Iterations]
   --> [Set Layers: Player, Enemy, Environment, Projectile]
   --> [Set Collision Matrix: 4 pairs]
   --> [Create Materials: ice, rubber]
   --> [Apply to objects]

Optimization Tips

Keep your implementation fast and efficient with these optimization tips:

Use primitive colliders (box, sphere, capsule) instead of mesh colliders for dynamic objects. Mesh colliders are 10x more expensive.
Put sleeping rigidbodies to rest. Objects that have not moved for 2 seconds should sleep — saves significant CPU.
Use higher fixed timestep on mobile (0.02 = 50Hz) to save CPU. 60Hz is ideal but 50Hz is 20% cheaper.
Limit solver iterations to 4-6 for most scenes. Only increase to 8-16 for stacking scenarios.