From cb419cce911edbf63ca782ef83969f60ce11d832 Mon Sep 17 00:00:00 2001
From: Christian Nicoloso <chnicoloso@gmail.com>
Date: Sun, 31 Jul 2022 18:55:24 -0700
Subject: [PATCH 1/6] add frictionGravity

---
 src/world/Narrowphase.test.ts | 48 +++++++++++++++++++++++++++++++++++
 src/world/Narrowphase.ts      |  2 +-
 src/world/World.test.ts       | 17 +++++++++++++
 src/world/World.ts            | 16 ++++++++++++
 4 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/src/world/Narrowphase.test.ts b/src/world/Narrowphase.test.ts
index 99c1125d9..7d95725ac 100644
--- a/src/world/Narrowphase.test.ts
+++ b/src/world/Narrowphase.test.ts
@@ -6,6 +6,7 @@ import { Sphere } from '../shapes/Sphere'
 import { Body } from '../objects/Body'
 import { World } from '../world/World'
 import { ContactEquation } from '../equations/ContactEquation'
+import { FrictionEquation } from '../equations/FrictionEquation'
 
 describe('Narrowphase', () => {
   test('sphere + sphere contact', () => {
@@ -63,6 +64,53 @@ describe('Narrowphase', () => {
 
     expect(result.length).toBe(1)
   })
+
+  test('should use frictionGravity to create friction equations', () => {
+    const gravity = new Vec3(0, 0, 0)
+    const frictionGravity = new Vec3(0, -9.81, 0)
+    const world = new World({ gravity, frictionGravity })
+
+    const narrowPhase = new Narrowphase(world)
+    const contacts: ContactEquation[] = []
+    const sphereShape = new Sphere(1)
+
+    const bodyA = new Body({ mass: 1 })
+    const bodyB = new Body({ mass: 1 })
+    bodyA.addShape(sphereShape)
+    bodyB.addShape(sphereShape)
+
+    narrowPhase.result = contacts
+    narrowPhase.sphereSphere(
+      sphereShape,
+      sphereShape,
+      new Vec3(0.5, 0, 0),
+      new Vec3(-0.5, 0, 0),
+      new Quaternion(),
+      new Quaternion(),
+      bodyA,
+      bodyB
+    )
+
+    expect(contacts.length).toBe(1)
+    const [contact] = contacts
+    const result: FrictionEquation[] = []
+
+    // No gravity, frictionGravity defined, friction.
+    narrowPhase.createFrictionEquationsFromContact(contact, result)
+    expect(result.length).toBe(2)
+    result.forEach((result) => {
+      expect(result.maxForce > 0).toBe(true)
+    })
+
+    // No gravity, no frictionGravity, no friction.
+    result.length = 0
+    world.frictionGravity = new Vec3(0, 0, 0)
+    narrowPhase.createFrictionEquationsFromContact(contact, result)
+    expect(result.length).toBe(2)
+    result.forEach((result) => {
+      expect(result.maxForce).toBe(0)
+    })
+  })
 })
 
 function createHeightfield() {
diff --git a/src/world/Narrowphase.ts b/src/world/Narrowphase.ts
index ca6c2f2ae..7f08448cb 100644
--- a/src/world/Narrowphase.ts
+++ b/src/world/Narrowphase.ts
@@ -224,7 +224,7 @@ export class Narrowphase {
 
     if (friction > 0) {
       // Create 2 tangent equations
-      const mug = friction * world.gravity.length()
+      const mug = friction * world.frictionGravity.length()
       let reducedMass = bodyA.invMass + bodyB.invMass
       if (reducedMass > 0) {
         reducedMass = 1 / reducedMass
diff --git a/src/world/World.test.ts b/src/world/World.test.ts
index cc5229c5f..b097136fa 100644
--- a/src/world/World.test.ts
+++ b/src/world/World.test.ts
@@ -259,4 +259,21 @@ describe('World', () => {
   test('using ObjectCollisionMatrix', () => {
     testCollisionMatrix(ObjectCollisionMatrix)
   })
+
+  test('frictionGravity: should default to world gravity', () => {
+    const gravity = new Vec3(0, -9.81, 0)
+    const world = new World({ gravity })
+
+    expect(world.gravity).toEqual(gravity)
+    expect(world.frictionGravity).toEqual(gravity)
+  })
+
+  test('frictionGravity: should allow overrides', () => {
+    const gravity = new Vec3(0, 0, 0)
+    const frictionGravity = new Vec3(0, -9.81, 0)
+    const world = new World({ gravity, frictionGravity })
+
+    expect(world.gravity).toEqual(gravity)
+    expect(world.frictionGravity).toEqual(frictionGravity)
+  })
 })
diff --git a/src/world/World.ts b/src/world/World.ts
index 9acd4e22e..cd497736d 100644
--- a/src/world/World.ts
+++ b/src/world/World.ts
@@ -79,6 +79,12 @@ export class World extends EventTarget {
    */
   gravity: Vec3
 
+  /**
+   * Gravity to use when approximating the friction max force (mu*mass*gravity).
+   * Use to enable friction in a World with a null gravity vector (no gravity).
+   */
+  frictionGravity: Vec3
+
   /**
    * The broadphase algorithm to use.
    * @default NaiveBroadphase
@@ -170,6 +176,10 @@ export class World extends EventTarget {
        * The gravity of the world.
        */
       gravity?: Vec3
+      /**
+       * Gravity to use when approximating the friction max force (mu*mass*gravity).
+       */
+      frictionGravity?: Vec3
       /**
        * Makes bodies go to sleep when they've been inactive.
        * @default false
@@ -211,10 +221,16 @@ export class World extends EventTarget {
     this.default_dt = 1 / 60
     this.nextId = 0
     this.gravity = new Vec3()
+    this.frictionGravity = new Vec3()
 
     if (options.gravity) {
       this.gravity.copy(options.gravity)
     }
+    if (options.frictionGravity) {
+      this.frictionGravity.copy(options.frictionGravity)
+    } else if (options.gravity) {
+      this.frictionGravity.copy(options.gravity)
+    }
 
     this.broadphase = options.broadphase !== undefined ? options.broadphase : new NaiveBroadphase()
     this.bodies = []

From b55b33caac17c5300c33d58ebd1f2f2eb1b42ae2 Mon Sep 17 00:00:00 2001
From: Christian Nicoloso <chnicoloso@gmail.com>
Date: Sun, 31 Jul 2022 19:17:36 -0700
Subject: [PATCH 2/6] update README

---
 readme.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/readme.md b/readme.md
index ea55c6cef..9cfe7e617 100644
--- a/readme.md
+++ b/readme.md
@@ -16,6 +16,7 @@ These minor changes and improvements were also made:
 - Add support for [Trigger bodies](https://pmndrs.github.io/cannon-es/examples/trigger). [#83](https://github.com/pmndrs/cannon-es/pull/83)
 - Deprecated properties and methods have been removed.
 - The [original cannon.js debugger](https://github.com/schteppe/cannon.js/blob/master/tools/threejs/CannonDebugRenderer.js), which shows the wireframes of each body, has been moved to its own repo [cannon-es-debugger](https://github.com/pmndrs/cannon-es-debugger).
+- Added a property `World.frictionGravity`, which will be used when computing the friction on two colliding bodies. The value defaults to `World.gravity` and allows for enabling friction in zero gravity. This addresses issue [#224](https://github.com/schteppe/cannon.js/issues/224) and follows the [pattern established for p2.js](https://github.com/schteppe/p2.js/blob/master/src/world/World.js#L88-L92).
 
 If instead you're using three.js in a **React** environment with [react-three-fiber](https://github.com/pmndrs/react-three-fiber), check out [use-cannon](https://github.com/pmndrs/use-cannon)! It's a wrapper around cannon-es.
 

From c7f6d0f7b9bd1b2df672f7a6bfe797d8d3d16dd8 Mon Sep 17 00:00:00 2001
From: Christian Nicoloso <chnicoloso@gmail.com>
Date: Tue, 2 Aug 2022 20:33:50 -0700
Subject: [PATCH 3/6] update dist

---
 dist/cannon-es.cjs.js | 16 +++++++++++++++-
 dist/cannon-es.d.ts   |  2 ++
 dist/cannon-es.js     | 16 +++++++++++++++-
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/dist/cannon-es.cjs.js b/dist/cannon-es.cjs.js
index 90cedfabe..c03b0c3a2 100644
--- a/dist/cannon-es.cjs.js
+++ b/dist/cannon-es.cjs.js
@@ -1801,6 +1801,8 @@ class Quaternion {
     target.x = bank;
   }
   /**
+   * Set the quaternion components given Euler angle representation.
+   *
    * @param order The order to apply angles: 'XYZ' or 'YXZ' or any other combination.
    *
    * See {@link https://www.mathworks.com/matlabcentral/fileexchange/20696-function-to-convert-between-dcm-euler-angles-quaternions-and-euler-vectors MathWorks} reference
@@ -10457,7 +10459,7 @@ class Narrowphase {
 
     if (friction > 0) {
       // Create 2 tangent equations
-      const mug = friction * world.gravity.length();
+      const mug = friction * world.frictionGravity.length();
       let reducedMass = bodyA.invMass + bodyB.invMass;
 
       if (reducedMass > 0) {
@@ -12115,6 +12117,11 @@ class World extends EventTarget {
    * The gravity of the world.
    */
 
+  /**
+   * Gravity to use when approximating the friction max force (mu*mass*gravity).
+   * Use to enable friction in a World with a null gravity vector (no gravity).
+   */
+
   /**
    * The broadphase algorithm to use.
    * @default NaiveBroadphase
@@ -12186,11 +12193,18 @@ class World extends EventTarget {
     this.default_dt = 1 / 60;
     this.nextId = 0;
     this.gravity = new Vec3();
+    this.frictionGravity = new Vec3();
 
     if (options.gravity) {
       this.gravity.copy(options.gravity);
     }
 
+    if (options.frictionGravity) {
+      this.frictionGravity.copy(options.frictionGravity);
+    } else if (options.gravity) {
+      this.frictionGravity.copy(options.gravity);
+    }
+
     this.broadphase = options.broadphase !== undefined ? options.broadphase : new NaiveBroadphase();
     this.bodies = [];
     this.hasActiveBodies = false;
diff --git a/dist/cannon-es.d.ts b/dist/cannon-es.d.ts
index 70687b9d8..599a5dbf4 100644
--- a/dist/cannon-es.d.ts
+++ b/dist/cannon-es.d.ts
@@ -799,6 +799,7 @@ declare module "world/World" {
         default_dt: number;
         nextId: number;
         gravity: Vec3;
+        frictionGravity: Vec3;
         broadphase: Broadphase;
         bodies: Body[];
         hasActiveBodies: boolean;
@@ -837,6 +838,7 @@ declare module "world/World" {
         lastCallTime?: number;
         constructor(options?: {
             gravity?: Vec3;
+            frictionGravity?: Vec3;
             allowSleep?: boolean;
             broadphase?: Broadphase;
             solver?: Solver;
diff --git a/dist/cannon-es.js b/dist/cannon-es.js
index 7e050371d..48afb20e8 100644
--- a/dist/cannon-es.js
+++ b/dist/cannon-es.js
@@ -1797,6 +1797,8 @@ class Quaternion {
     target.x = bank;
   }
   /**
+   * Set the quaternion components given Euler angle representation.
+   *
    * @param order The order to apply angles: 'XYZ' or 'YXZ' or any other combination.
    *
    * See {@link https://www.mathworks.com/matlabcentral/fileexchange/20696-function-to-convert-between-dcm-euler-angles-quaternions-and-euler-vectors MathWorks} reference
@@ -10453,7 +10455,7 @@ class Narrowphase {
 
     if (friction > 0) {
       // Create 2 tangent equations
-      const mug = friction * world.gravity.length();
+      const mug = friction * world.frictionGravity.length();
       let reducedMass = bodyA.invMass + bodyB.invMass;
 
       if (reducedMass > 0) {
@@ -12111,6 +12113,11 @@ class World extends EventTarget {
    * The gravity of the world.
    */
 
+  /**
+   * Gravity to use when approximating the friction max force (mu*mass*gravity).
+   * Use to enable friction in a World with a null gravity vector (no gravity).
+   */
+
   /**
    * The broadphase algorithm to use.
    * @default NaiveBroadphase
@@ -12182,11 +12189,18 @@ class World extends EventTarget {
     this.default_dt = 1 / 60;
     this.nextId = 0;
     this.gravity = new Vec3();
+    this.frictionGravity = new Vec3();
 
     if (options.gravity) {
       this.gravity.copy(options.gravity);
     }
 
+    if (options.frictionGravity) {
+      this.frictionGravity.copy(options.frictionGravity);
+    } else if (options.gravity) {
+      this.frictionGravity.copy(options.gravity);
+    }
+
     this.broadphase = options.broadphase !== undefined ? options.broadphase : new NaiveBroadphase();
     this.bodies = [];
     this.hasActiveBodies = false;

From b405f6d3d2b0652d9911a8ad3aed6a28e2ee5d1c Mon Sep 17 00:00:00 2001
From: Christian Nicoloso <chnicoloso@gmail.com>
Date: Sat, 6 Aug 2022 13:37:22 -0700
Subject: [PATCH 4/6] keep global gravity as default friction gravity

---
 src/world/Narrowphase.test.ts | 41 ++++++++++++++++++++++++++++++++++-
 src/world/Narrowphase.ts      |  3 ++-
 src/world/World.test.ts       |  6 ++---
 src/world/World.ts            |  8 +++----
 4 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/src/world/Narrowphase.test.ts b/src/world/Narrowphase.test.ts
index 7d95725ac..3b937c336 100644
--- a/src/world/Narrowphase.test.ts
+++ b/src/world/Narrowphase.test.ts
@@ -65,7 +65,46 @@ describe('Narrowphase', () => {
     expect(result.length).toBe(1)
   })
 
-  test('should use frictionGravity to create friction equations', () => {
+  test('should default to using global gravity to create friction equations', () => {
+    const gravity = new Vec3(0, -9.81, 0)
+    const world = new World({ gravity })
+    // No frictionGravity override.
+    expect(world.frictionGravity).toBeUndefined()
+
+    const narrowPhase = new Narrowphase(world)
+    const contacts: ContactEquation[] = []
+    const sphereShape = new Sphere(1)
+
+    const bodyA = new Body({ mass: 1 })
+    const bodyB = new Body({ mass: 1 })
+    bodyA.addShape(sphereShape)
+    bodyB.addShape(sphereShape)
+
+    narrowPhase.result = contacts
+    narrowPhase.sphereSphere(
+      sphereShape,
+      sphereShape,
+      new Vec3(0.5, 0, 0),
+      new Vec3(-0.5, 0, 0),
+      new Quaternion(),
+      new Quaternion(),
+      bodyA,
+      bodyB
+    )
+
+    expect(contacts.length).toBe(1)
+    const [contact] = contacts
+    const result: FrictionEquation[] = []
+
+    // No frictionGravity, should use global gravity.
+    narrowPhase.createFrictionEquationsFromContact(contact, result)
+    expect(result.length).toBe(2)
+    result.forEach((result) => {
+      expect(result.maxForce > 0).toBe(true)
+    })
+  })
+
+  test('if provided, should use frictionGravity to create friction equations', () => {
     const gravity = new Vec3(0, 0, 0)
     const frictionGravity = new Vec3(0, -9.81, 0)
     const world = new World({ gravity, frictionGravity })
diff --git a/src/world/Narrowphase.ts b/src/world/Narrowphase.ts
index 7f08448cb..9c7c978ea 100644
--- a/src/world/Narrowphase.ts
+++ b/src/world/Narrowphase.ts
@@ -224,7 +224,8 @@ export class Narrowphase {
 
     if (friction > 0) {
       // Create 2 tangent equations
-      const mug = friction * world.frictionGravity.length()
+      // Users may provide a force different from global gravity to use when computing contact friction.
+      const mug = friction * (world.frictionGravity || world.gravity).length()
       let reducedMass = bodyA.invMass + bodyB.invMass
       if (reducedMass > 0) {
         reducedMass = 1 / reducedMass
diff --git a/src/world/World.test.ts b/src/world/World.test.ts
index b097136fa..f657f410a 100644
--- a/src/world/World.test.ts
+++ b/src/world/World.test.ts
@@ -260,15 +260,15 @@ describe('World', () => {
     testCollisionMatrix(ObjectCollisionMatrix)
   })
 
-  test('frictionGravity: should default to world gravity', () => {
+  test('frictionGravity: should be undefined by default', () => {
     const gravity = new Vec3(0, -9.81, 0)
     const world = new World({ gravity })
 
     expect(world.gravity).toEqual(gravity)
-    expect(world.frictionGravity).toEqual(gravity)
+    expect(world.frictionGravity).toBeUndefined()
   })
 
-  test('frictionGravity: should allow overrides', () => {
+  test('frictionGravity: should be configurable', () => {
     const gravity = new Vec3(0, 0, 0)
     const frictionGravity = new Vec3(0, -9.81, 0)
     const world = new World({ gravity, frictionGravity })
diff --git a/src/world/World.ts b/src/world/World.ts
index cd497736d..9d917cb80 100644
--- a/src/world/World.ts
+++ b/src/world/World.ts
@@ -81,9 +81,10 @@ export class World extends EventTarget {
 
   /**
    * Gravity to use when approximating the friction max force (mu*mass*gravity).
+   * If undefined, global gravity will be used.
    * Use to enable friction in a World with a null gravity vector (no gravity).
    */
-  frictionGravity: Vec3
+  frictionGravity?: Vec3
 
   /**
    * The broadphase algorithm to use.
@@ -178,6 +179,7 @@ export class World extends EventTarget {
       gravity?: Vec3
       /**
        * Gravity to use when approximating the friction max force (mu*mass*gravity).
+       * If undefined, global gravity will be used.
        */
       frictionGravity?: Vec3
       /**
@@ -221,15 +223,13 @@ export class World extends EventTarget {
     this.default_dt = 1 / 60
     this.nextId = 0
     this.gravity = new Vec3()
-    this.frictionGravity = new Vec3()
 
     if (options.gravity) {
       this.gravity.copy(options.gravity)
     }
     if (options.frictionGravity) {
+      this.frictionGravity = new Vec3()
       this.frictionGravity.copy(options.frictionGravity)
-    } else if (options.gravity) {
-      this.frictionGravity.copy(options.gravity)
     }
 
     this.broadphase = options.broadphase !== undefined ? options.broadphase : new NaiveBroadphase()

From e43146ebf47375cea8b7ee72ab14bc8aabea9123 Mon Sep 17 00:00:00 2001
From: Christian Nicoloso <chnicoloso@gmail.com>
Date: Sat, 6 Aug 2022 13:44:25 -0700
Subject: [PATCH 5/6] revert dist to origin

---
 dist/cannon-es.cjs.js | 16 +---------------
 dist/cannon-es.d.ts   |  2 --
 dist/cannon-es.js     | 16 +---------------
 3 files changed, 2 insertions(+), 32 deletions(-)

diff --git a/dist/cannon-es.cjs.js b/dist/cannon-es.cjs.js
index c03b0c3a2..90cedfabe 100644
--- a/dist/cannon-es.cjs.js
+++ b/dist/cannon-es.cjs.js
@@ -1801,8 +1801,6 @@ class Quaternion {
     target.x = bank;
   }
   /**
-   * Set the quaternion components given Euler angle representation.
-   *
    * @param order The order to apply angles: 'XYZ' or 'YXZ' or any other combination.
    *
    * See {@link https://www.mathworks.com/matlabcentral/fileexchange/20696-function-to-convert-between-dcm-euler-angles-quaternions-and-euler-vectors MathWorks} reference
@@ -10459,7 +10457,7 @@ class Narrowphase {
 
     if (friction > 0) {
       // Create 2 tangent equations
-      const mug = friction * world.frictionGravity.length();
+      const mug = friction * world.gravity.length();
       let reducedMass = bodyA.invMass + bodyB.invMass;
 
       if (reducedMass > 0) {
@@ -12117,11 +12115,6 @@ class World extends EventTarget {
    * The gravity of the world.
    */
 
-  /**
-   * Gravity to use when approximating the friction max force (mu*mass*gravity).
-   * Use to enable friction in a World with a null gravity vector (no gravity).
-   */
-
   /**
    * The broadphase algorithm to use.
    * @default NaiveBroadphase
@@ -12193,18 +12186,11 @@ class World extends EventTarget {
     this.default_dt = 1 / 60;
     this.nextId = 0;
     this.gravity = new Vec3();
-    this.frictionGravity = new Vec3();
 
     if (options.gravity) {
       this.gravity.copy(options.gravity);
     }
 
-    if (options.frictionGravity) {
-      this.frictionGravity.copy(options.frictionGravity);
-    } else if (options.gravity) {
-      this.frictionGravity.copy(options.gravity);
-    }
-
     this.broadphase = options.broadphase !== undefined ? options.broadphase : new NaiveBroadphase();
     this.bodies = [];
     this.hasActiveBodies = false;
diff --git a/dist/cannon-es.d.ts b/dist/cannon-es.d.ts
index 599a5dbf4..70687b9d8 100644
--- a/dist/cannon-es.d.ts
+++ b/dist/cannon-es.d.ts
@@ -799,7 +799,6 @@ declare module "world/World" {
         default_dt: number;
         nextId: number;
         gravity: Vec3;
-        frictionGravity: Vec3;
         broadphase: Broadphase;
         bodies: Body[];
         hasActiveBodies: boolean;
@@ -838,7 +837,6 @@ declare module "world/World" {
         lastCallTime?: number;
         constructor(options?: {
             gravity?: Vec3;
-            frictionGravity?: Vec3;
             allowSleep?: boolean;
             broadphase?: Broadphase;
             solver?: Solver;
diff --git a/dist/cannon-es.js b/dist/cannon-es.js
index 48afb20e8..7e050371d 100644
--- a/dist/cannon-es.js
+++ b/dist/cannon-es.js
@@ -1797,8 +1797,6 @@ class Quaternion {
     target.x = bank;
   }
   /**
-   * Set the quaternion components given Euler angle representation.
-   *
    * @param order The order to apply angles: 'XYZ' or 'YXZ' or any other combination.
    *
    * See {@link https://www.mathworks.com/matlabcentral/fileexchange/20696-function-to-convert-between-dcm-euler-angles-quaternions-and-euler-vectors MathWorks} reference
@@ -10455,7 +10453,7 @@ class Narrowphase {
 
     if (friction > 0) {
       // Create 2 tangent equations
-      const mug = friction * world.frictionGravity.length();
+      const mug = friction * world.gravity.length();
       let reducedMass = bodyA.invMass + bodyB.invMass;
 
       if (reducedMass > 0) {
@@ -12113,11 +12111,6 @@ class World extends EventTarget {
    * The gravity of the world.
    */
 
-  /**
-   * Gravity to use when approximating the friction max force (mu*mass*gravity).
-   * Use to enable friction in a World with a null gravity vector (no gravity).
-   */
-
   /**
    * The broadphase algorithm to use.
    * @default NaiveBroadphase
@@ -12189,18 +12182,11 @@ class World extends EventTarget {
     this.default_dt = 1 / 60;
     this.nextId = 0;
     this.gravity = new Vec3();
-    this.frictionGravity = new Vec3();
 
     if (options.gravity) {
       this.gravity.copy(options.gravity);
     }
 
-    if (options.frictionGravity) {
-      this.frictionGravity.copy(options.frictionGravity);
-    } else if (options.gravity) {
-      this.frictionGravity.copy(options.gravity);
-    }
-
     this.broadphase = options.broadphase !== undefined ? options.broadphase : new NaiveBroadphase();
     this.bodies = [];
     this.hasActiveBodies = false;

From 4f7cb4de054bcd74c23987e5dc0683576e96f1b7 Mon Sep 17 00:00:00 2001
From: Christian Nicoloso <chnicoloso@gmail.com>
Date: Tue, 9 Aug 2022 18:57:45 -0700
Subject: [PATCH 6/6] update readme

---
 readme.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/readme.md b/readme.md
index 9cfe7e617..658c2d610 100644
--- a/readme.md
+++ b/readme.md
@@ -16,7 +16,7 @@ These minor changes and improvements were also made:
 - Add support for [Trigger bodies](https://pmndrs.github.io/cannon-es/examples/trigger). [#83](https://github.com/pmndrs/cannon-es/pull/83)
 - Deprecated properties and methods have been removed.
 - The [original cannon.js debugger](https://github.com/schteppe/cannon.js/blob/master/tools/threejs/CannonDebugRenderer.js), which shows the wireframes of each body, has been moved to its own repo [cannon-es-debugger](https://github.com/pmndrs/cannon-es-debugger).
-- Added a property `World.frictionGravity`, which will be used when computing the friction on two colliding bodies. The value defaults to `World.gravity` and allows for enabling friction in zero gravity. This addresses issue [#224](https://github.com/schteppe/cannon.js/issues/224) and follows the [pattern established for p2.js](https://github.com/schteppe/p2.js/blob/master/src/world/World.js#L88-L92).
+- Added optional property `World.frictionGravity: Vec3` which can be set to customize the force used when computing the friction between two colliding bodies. If `undefined`, `World.gravity` will be used. This property is useful to enable friction in zero gravity. This addresses issue [#224](https://github.com/schteppe/cannon.js/issues/224) and follows the [pattern established for p2.js](https://github.com/schteppe/p2.js/blob/master/src/world/World.js#L88-L92).
 
 If instead you're using three.js in a **React** environment with [react-three-fiber](https://github.com/pmndrs/react-three-fiber), check out [use-cannon](https://github.com/pmndrs/use-cannon)! It's a wrapper around cannon-es.