# Physics with Cannon

## Description

Animation can also be achieved using a Physics library. We can use a library called Cannon.js. But, rather than using the original Cannon.js, which is no longer maintained, we can install a newer fork of it named Cannon-es instead.

The Cannon physics library is ideal for simulating rigid bodies. You don't have to use it with Three.js, but it was originally built to be used with Three.js, so it will be quite easy to begin using in your project.

We will use it to make objects move and interact in a more realistic way and provide collision detection possibilities.

## Basic Concepts

• Shape : A geometrical shape, such as a sphere, cube or plane, used for the the physics calculations.
• Rigid Body : A rigid body has a shape and a number of other properties used in the calculations such as mass and inertia.
• Constraint : A 3D body has 6 degrees of freedom, 3 for position and three to describe the rotation vector. A constraint is a limit on one of the degrees of freedom.
• Contact constraint : A type of constraint to simulate friction and restitution. These are like the faces of an object where the constraint is applied.
• World : A collection of bodies and constraints that interact together.
• Solver : The algorithm that is passed over the bodies and constraints to calculate there physical properties and adjust them accordingly.

## Collision Detection

Collision detection algorithms determine what pairs of objects may be colliding. Collision detection is a computationally expensive process, so various methods can be used to simplify the collision detection.

• Narrowphase : Outright body vs body collision detection. This is the most computationally expensive.
• Broadphase : Is a compromise on Narrowphase where various other techniques can be used to improve collision detection performance.

Cannon provides several options for broadphase detection.

Phase Description
NaiveBroadphase Default. The NaiveBroadphase looks at all possible pairs without restriction, therefore it has complexity N^2. It is similar to the Narrowphase technique, except it decides first whether objects are close enough before checking if there bodies touch. NaiveBroadphase is the default and is suitable for the most common use cases, but becomes less performant if there are many objects in the physics world.
SAPBroadphase The Sweep and Prune algorithm sorts bodies along an axis and then moves down that list finding pairs by looking at body size and position of the next bodies. For best performance, choose an axis that the bodies are spread out more on. Set 0 for X axis, 1 for Y axis and 2 for Z axis. Default axisIndex is 0 (X axis). ; E.g.,
`// TypeScript`
`world.broadphase = new CANNON.SAPBroadphase(world)`
`;(world.broadphase as CANNON.SAPBroadphase).axisIndex = 2`
GridBroadphase Axis aligned uniform grid broadphase. Divides space into a grid of cells. Bodies are placed into the cells they overlap and bodies in the same cell are paired. GridBroadphase needs to know the size of the space ahead of time. Set number of cells when you create the object. Default number of cells is X = 10, Y = 10, Z = 10.

## Iterations

The Solver algorithms decide what force to add to bodies in contact. The solver is iterative, which means that it solves the equations incrementally on each animation pass. It will get closer to the solution for each iteration during the loop. A number too low for the solver iterations will result in increasingly inaccurate contact forces, which can appear as jittering or vibrations on the object, and a higher number will increase precision and stability, but also compromise performance.

The default solver iterations is 10.

``````//JavaScript (Cannon.js version)
world.solver.iterations = 10

//TypeScript (Cannon-es version)
;(world.solver as CANNON.GSSolver).iterations = 10
``````

## Supported Cannon.js Shape Collisions

. Box Sphere Cylinder Plane Convex Trimesh
Box
Sphere
Cylinder
Plane
Convex
Trimesh

## Setup

Install Cannon-es

``````npm install cannon-es --save-dev
``````

## Start Scripts

### ./src/client/client.ts

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233``` ``````import * as THREE from 'three' import { OrbitControls } from 'three/examples/jsm/controls/OrbitControls' import Stats from 'three/examples/jsm/libs/stats.module' import { GUI } from 'dat.gui' import * as CANNON from 'cannon-es' const scene = new THREE.Scene() scene.add(new THREE.AxesHelper(5)) const light1 = new THREE.SpotLight(0xffffff, 100) light1.position.set(2.5, 5, 5) light1.angle = Math.PI / 4 light1.penumbra = 0.5 light1.castShadow = true light1.shadow.mapSize.width = 1024 light1.shadow.mapSize.height = 1024 light1.shadow.camera.near = 0.5 light1.shadow.camera.far = 20 scene.add(light1) const light2 = new THREE.SpotLight(0xffffff, 100) light2.position.set(-2.5, 5, 5) light2.angle = Math.PI / 4 light2.penumbra = 0.5 light2.castShadow = true light2.shadow.mapSize.width = 1024 light2.shadow.mapSize.height = 1024 light2.shadow.camera.near = 0.5 light2.shadow.camera.far = 20 scene.add(light2) const camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 0.1, 1000 ) camera.position.set(0, 2, 4) const renderer = new THREE.WebGLRenderer() renderer.setSize(window.innerWidth, window.innerHeight) renderer.shadowMap.enabled = true document.body.appendChild(renderer.domElement) const controls = new OrbitControls(camera, renderer.domElement) controls.enableDamping = true controls.target.y = 0.5 // const world = new CANNON.World() // world.gravity.set(0, -9.82, 0) // world.broadphase = new CANNON.NaiveBroadphase() // ;(world.solver as CANNON.GSSolver).iterations = 10 // world.allowSleep = true const normalMaterial = new THREE.MeshNormalMaterial() const phongMaterial = new THREE.MeshPhongMaterial() const cubeGeometry = new THREE.BoxGeometry(1, 1, 1) const cubeMesh = new THREE.Mesh(cubeGeometry, normalMaterial) cubeMesh.position.x = -3 cubeMesh.position.y = 3 cubeMesh.castShadow = true scene.add(cubeMesh) // const cubeShape = new CANNON.Box(new CANNON.Vec3(0.5, 0.5, 0.5)) // const cubeBody = new CANNON.Body({ mass: 1 }) // cubeBody.addShape(cubeShape) // cubeBody.position.x = cubeMesh.position.x // cubeBody.position.y = cubeMesh.position.y // cubeBody.position.z = cubeMesh.position.z // world.addBody(cubeBody) const sphereGeometry = new THREE.SphereGeometry() const sphereMesh = new THREE.Mesh(sphereGeometry, normalMaterial) sphereMesh.position.x = -1 sphereMesh.position.y = 3 sphereMesh.castShadow = true scene.add(sphereMesh) // const sphereShape = new CANNON.Sphere(1) // const sphereBody = new CANNON.Body({ mass: 1 }) // sphereBody.addShape(sphereShape) // sphereBody.position.x = sphereMesh.position.x // sphereBody.position.y = sphereMesh.position.y // sphereBody.position.z = sphereMesh.position.z // world.addBody(sphereBody) const icosahedronGeometry = new THREE.IcosahedronGeometry(1, 0) const icosahedronMesh = new THREE.Mesh(icosahedronGeometry, normalMaterial) icosahedronMesh.position.x = 1 icosahedronMesh.position.y = 3 icosahedronMesh.castShadow = true scene.add(icosahedronMesh) // let position = (icosahedronMesh.geometry.attributes.position as THREE.BufferAttribute).array // const icosahedronPoints: CANNON.Vec3[] = [] // for (let i = 0; i < position.length; i += 3) { // icosahedronPoints.push(new CANNON.Vec3(position[i], position[i + 1], position[i + 2])) // } // const icosahedronFaces: number[][] = [] // for (let i = 0; i < position.length / 3; i += 3) { // icosahedronFaces.push([i, i + 1, i + 2]) // } // const icosahedronShape = new CANNON.ConvexPolyhedron({ // vertices: icosahedronPoints, // faces: icosahedronFaces, // }) // const icosahedronBody = new CANNON.Body({ mass: 1 }) // icosahedronBody.addShape(icosahedronShape) // icosahedronBody.position.x = icosahedronMesh.position.x // icosahedronBody.position.y = icosahedronMesh.position.y // icosahedronBody.position.z = icosahedronMesh.position.z // world.addBody(icosahedronBody) const torusKnotGeometry = new THREE.TorusKnotGeometry() const torusKnotMesh = new THREE.Mesh(torusKnotGeometry, normalMaterial) torusKnotMesh.position.x = 4 torusKnotMesh.position.y = 3 torusKnotMesh.castShadow = true scene.add(torusKnotMesh) // position = (torusKnotMesh.geometry.attributes.position as THREE.BufferAttribute).array // const torusKnotPoints: CANNON.Vec3[] = [] // for (let i = 0; i < position.length; i += 3) { // torusKnotPoints.push(new CANNON.Vec3(position[i], position[i + 1], position[i + 2])); // } // const torusKnotFaces: number[][] = [] // for (let i = 0; i < position.length / 3; i += 3) { // torusKnotFaces.push([i, i + 1, i + 2]) // } // const torusKnotShape = new CANNON.ConvexPolyhedron({ // vertices: torusKnotPoints, // faces: torusKnotFaces, // }) // const torusKnotShape = CreateTrimesh(torusKnotMesh.geometry) // const torusKnotBody = new CANNON.Body({ mass: 1 }) // torusKnotBody.addShape(torusKnotShape) // torusKnotBody.position.x = torusKnotMesh.position.x // torusKnotBody.position.y = torusKnotMesh.position.y // torusKnotBody.position.z = torusKnotMesh.position.z // world.addBody(torusKnotBody) // function CreateTrimesh(geometry: THREE.BufferGeometry) { // const vertices = (geometry.attributes.position as THREE.BufferAttribute).array // const indices = Object.keys(vertices).map(Number) // return new CANNON.Trimesh(vertices as unknown as number[], indices) // } const planeGeometry = new THREE.PlaneGeometry(25, 25) const planeMesh = new THREE.Mesh(planeGeometry, phongMaterial) planeMesh.rotateX(-Math.PI / 2) planeMesh.receiveShadow = true scene.add(planeMesh) // const planeShape = new CANNON.Plane() // const planeBody = new CANNON.Body({ mass: 0 }) // planeBody.addShape(planeShape) // planeBody.quaternion.setFromAxisAngle(new CANNON.Vec3(1, 0, 0), -Math.PI / 2) // world.addBody(planeBody) window.addEventListener('resize', onWindowResize, false) function onWindowResize() { camera.aspect = window.innerWidth / window.innerHeight camera.updateProjectionMatrix() renderer.setSize(window.innerWidth, window.innerHeight) render() } const stats = new Stats() document.body.appendChild(stats.dom) const gui = new GUI() // const physicsFolder = gui.addFolder('Physics') // physicsFolder.add(world.gravity, 'x', -10.0, 10.0, 0.1) // physicsFolder.add(world.gravity, 'y', -10.0, 10.0, 0.1) // physicsFolder.add(world.gravity, 'z', -10.0, 10.0, 0.1) // physicsFolder.open() // const clock = new THREE.Clock() // let delta function animate() { requestAnimationFrame(animate) controls.update() // delta = clock.getDelta() // //delta = Math.min(clock.getDelta(), 0.1) // world.step(delta) // Copy coordinates from Cannon to Three.js // cubeMesh.position.set(cubeBody.position.x, cubeBody.position.y, cubeBody.position.z) // cubeMesh.quaternion.set( // cubeBody.quaternion.x, // cubeBody.quaternion.y, // cubeBody.quaternion.z, // cubeBody.quaternion.w // ) // sphereMesh.position.set(sphereBody.position.x, sphereBody.position.y, sphereBody.position.z) // sphereMesh.quaternion.set( // sphereBody.quaternion.x, // sphereBody.quaternion.y, // sphereBody.quaternion.z, // sphereBody.quaternion.w // ) // icosahedronMesh.position.set( // icosahedronBody.position.x, // icosahedronBody.position.y, // icosahedronBody.position.z // ) // icosahedronMesh.quaternion.set( // icosahedronBody.quaternion.x, // icosahedronBody.quaternion.y, // icosahedronBody.quaternion.z, // icosahedronBody.quaternion.w // ) // torusKnotMesh.position.set( // torusKnotBody.position.x, // torusKnotBody.position.y, // torusKnotBody.position.z // ) // torusKnotMesh.quaternion.set( // torusKnotBody.quaternion.x, // torusKnotBody.quaternion.y, // torusKnotBody.quaternion.z, // torusKnotBody.quaternion.w // ) render() stats.update() } function render() { renderer.render(scene, camera) } animate() ``````

## Final Scripts

### ./src/client/client.ts

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243``` ``````import * as THREE from 'three' import { OrbitControls } from 'three/examples/jsm/controls/OrbitControls' import Stats from 'three/examples/jsm/libs/stats.module' import { GUI } from 'dat.gui' import * as CANNON from 'cannon-es' const scene = new THREE.Scene() scene.add(new THREE.AxesHelper(5)) const light1 = new THREE.SpotLight(0xffffff, 100) light1.position.set(2.5, 5, 5) light1.angle = Math.PI / 4 light1.penumbra = 0.5 light1.castShadow = true light1.shadow.mapSize.width = 1024 light1.shadow.mapSize.height = 1024 light1.shadow.camera.near = 0.5 light1.shadow.camera.far = 20 scene.add(light1) const light2 = new THREE.SpotLight(0xffffff, 100) light2.position.set(-2.5, 5, 5) light2.angle = Math.PI / 4 light2.penumbra = 0.5 light2.castShadow = true light2.shadow.mapSize.width = 1024 light2.shadow.mapSize.height = 1024 light2.shadow.camera.near = 0.5 light2.shadow.camera.far = 20 scene.add(light2) const camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 0.1, 1000 ) camera.position.set(0, 2, 4) const renderer = new THREE.WebGLRenderer() renderer.setSize(window.innerWidth, window.innerHeight) renderer.shadowMap.enabled = true document.body.appendChild(renderer.domElement) const controls = new OrbitControls(camera, renderer.domElement) controls.enableDamping = true controls.target.y = 0.5 const world = new CANNON.World() world.gravity.set(0, -9.82, 0) // world.broadphase = new CANNON.NaiveBroadphase() // ;(world.solver as CANNON.GSSolver).iterations = 10 // world.allowSleep = true const normalMaterial = new THREE.MeshNormalMaterial() const phongMaterial = new THREE.MeshPhongMaterial() const cubeGeometry = new THREE.BoxGeometry(1, 1, 1) const cubeMesh = new THREE.Mesh(cubeGeometry, normalMaterial) cubeMesh.position.x = -3 cubeMesh.position.y = 3 cubeMesh.castShadow = true scene.add(cubeMesh) const cubeShape = new CANNON.Box(new CANNON.Vec3(0.5, 0.5, 0.5)) const cubeBody = new CANNON.Body({ mass: 1 }) cubeBody.addShape(cubeShape) cubeBody.position.x = cubeMesh.position.x cubeBody.position.y = cubeMesh.position.y cubeBody.position.z = cubeMesh.position.z world.addBody(cubeBody) const sphereGeometry = new THREE.SphereGeometry() const sphereMesh = new THREE.Mesh(sphereGeometry, normalMaterial) sphereMesh.position.x = -1 sphereMesh.position.y = 3 sphereMesh.castShadow = true scene.add(sphereMesh) const sphereShape = new CANNON.Sphere(1) const sphereBody = new CANNON.Body({ mass: 1 }) sphereBody.addShape(sphereShape) sphereBody.position.x = sphereMesh.position.x sphereBody.position.y = sphereMesh.position.y sphereBody.position.z = sphereMesh.position.z world.addBody(sphereBody) const icosahedronGeometry = new THREE.IcosahedronGeometry(1, 0) const icosahedronMesh = new THREE.Mesh(icosahedronGeometry, normalMaterial) icosahedronMesh.position.x = 1 icosahedronMesh.position.y = 3 icosahedronMesh.castShadow = true scene.add(icosahedronMesh) const position = ( icosahedronMesh.geometry.attributes.position as THREE.BufferAttribute ).array const icosahedronPoints: CANNON.Vec3[] = [] for (let i = 0; i < position.length; i += 3) { icosahedronPoints.push( new CANNON.Vec3(position[i], position[i + 1], position[i + 2]) ) } const icosahedronFaces: number[][] = [] for (let i = 0; i < position.length / 3; i += 3) { icosahedronFaces.push([i, i + 1, i + 2]) } const icosahedronShape = new CANNON.ConvexPolyhedron({ vertices: icosahedronPoints, faces: icosahedronFaces, }) const icosahedronBody = new CANNON.Body({ mass: 1 }) icosahedronBody.addShape(icosahedronShape) icosahedronBody.position.x = icosahedronMesh.position.x icosahedronBody.position.y = icosahedronMesh.position.y icosahedronBody.position.z = icosahedronMesh.position.z world.addBody(icosahedronBody) const torusKnotGeometry = new THREE.TorusKnotGeometry() const torusKnotMesh = new THREE.Mesh(torusKnotGeometry, normalMaterial) torusKnotMesh.position.x = 4 torusKnotMesh.position.y = 3 torusKnotMesh.castShadow = true scene.add(torusKnotMesh) // position = (torusKnotMesh.geometry.attributes.position as THREE.BufferAttribute).array // const torusKnotPoints: CANNON.Vec3[] = [] // for (let i = 0; i < position.length; i += 3) { // torusKnotPoints.push(new CANNON.Vec3(position[i], position[i + 1], position[i + 2])); // } // const torusKnotFaces: number[][] = [] // for (let i = 0; i < position.length / 3; i += 3) { // torusKnotFaces.push([i, i + 1, i + 2]) // } // const torusKnotShape = new CANNON.ConvexPolyhedron(torusKnotPoints, torusKnotFaces) const torusKnotShape = CreateTrimesh(torusKnotMesh.geometry) const torusKnotBody = new CANNON.Body({ mass: 1 }) torusKnotBody.addShape(torusKnotShape) torusKnotBody.position.x = torusKnotMesh.position.x torusKnotBody.position.y = torusKnotMesh.position.y torusKnotBody.position.z = torusKnotMesh.position.z world.addBody(torusKnotBody) function CreateTrimesh(geometry: THREE.BufferGeometry) { const vertices = (geometry.attributes.position as THREE.BufferAttribute) .array const indices = Object.keys(vertices).map(Number) return new CANNON.Trimesh(vertices as unknown as number[], indices) } const planeGeometry = new THREE.PlaneGeometry(25, 25) const planeMesh = new THREE.Mesh(planeGeometry, phongMaterial) planeMesh.rotateX(-Math.PI / 2) planeMesh.receiveShadow = true scene.add(planeMesh) const planeShape = new CANNON.Plane() const planeBody = new CANNON.Body({ mass: 0 }) planeBody.addShape(planeShape) planeBody.quaternion.setFromAxisAngle(new CANNON.Vec3(1, 0, 0), -Math.PI / 2) world.addBody(planeBody) window.addEventListener('resize', onWindowResize, false) function onWindowResize() { camera.aspect = window.innerWidth / window.innerHeight camera.updateProjectionMatrix() renderer.setSize(window.innerWidth, window.innerHeight) render() } const stats = new Stats() document.body.appendChild(stats.dom) const gui = new GUI() const physicsFolder = gui.addFolder('Physics') physicsFolder.add(world.gravity, 'x', -10.0, 10.0, 0.1) physicsFolder.add(world.gravity, 'y', -10.0, 10.0, 0.1) physicsFolder.add(world.gravity, 'z', -10.0, 10.0, 0.1) physicsFolder.open() const clock = new THREE.Clock() let delta function animate() { requestAnimationFrame(animate) controls.update() //delta = clock.getDelta() delta = Math.min(clock.getDelta(), 0.1) world.step(delta) // Copy coordinates from Cannon to Three.js cubeMesh.position.set( cubeBody.position.x, cubeBody.position.y, cubeBody.position.z ) cubeMesh.quaternion.set( cubeBody.quaternion.x, cubeBody.quaternion.y, cubeBody.quaternion.z, cubeBody.quaternion.w ) sphereMesh.position.set( sphereBody.position.x, sphereBody.position.y, sphereBody.position.z ) sphereMesh.quaternion.set( sphereBody.quaternion.x, sphereBody.quaternion.y, sphereBody.quaternion.z, sphereBody.quaternion.w ) icosahedronMesh.position.set( icosahedronBody.position.x, icosahedronBody.position.y, icosahedronBody.position.z ) icosahedronMesh.quaternion.set( icosahedronBody.quaternion.x, icosahedronBody.quaternion.y, icosahedronBody.quaternion.z, icosahedronBody.quaternion.w ) torusKnotMesh.position.set( torusKnotBody.position.x, torusKnotBody.position.y, torusKnotBody.position.z ) torusKnotMesh.quaternion.set( torusKnotBody.quaternion.x, torusKnotBody.quaternion.y, torusKnotBody.quaternion.z, torusKnotBody.quaternion.w ) render() stats.update() } function render() { renderer.render(scene, camera) } animate() ``````

## Troubleshooting

### geometry.attributes.position.array error : Property 'array' does not exist on type 'BufferAttribute | InterleavedBufferAttribute | GLBufferAttribute'

Since the addition of the `GLBufferAttribute` as a new type of `BufferGeometry.attributes`, it does not contain the `array` property. So, we now need to cast the attribute `as THREE.BufferAttribute` when we want to use a property or method of a `BufferAttribute` that isn't included in the `GLBufferAttribute` type.

E.g.,

@three/types@0.148 and earlier

``````const position = geometry.attributes.position.array
const normals = geometry.attributes.normal.array
const uvs = geometry.attributes.uv.array
``````

@three/types@0.149 and later

``````const position = (geometry.attributes.position as THREE.BufferAttribute).array
const normals = (geometry.attributes.normal as THREE.BufferAttribute).array
const uvs = (geometry.attributes.uv as THREE.BufferAttribute).array
``````

Cannon.js (Original)

Cannon-es (Maintained Fork)

Cannon.js Parameter Tweaking

International System of Units (Wikipedia)

Cannon.js (Wikipedia)