Extend RigidBodyComponent to include useGravity and gravity

src/framework/components/rigid-body/component.js

@@ -1,8 +1,11 @@
+import { Debug } from '../../../core/debug.js';
+
 import { Quat } from '../../../core/math/quat.js';
 import { Vec3 } from '../../../core/math/vec3.js';
 
 import {
     BODYFLAG_KINEMATIC_OBJECT, BODYTYPE_STATIC,
+    BODYFLAG_GRAVITY_WORLD_ENABLE, BODYFLAG_GRAVITY_WORLD_DISABLE,
     BODYGROUP_DYNAMIC, BODYGROUP_KINEMATIC, BODYGROUP_STATIC,
     BODYMASK_ALL, BODYMASK_NOT_STATIC,
     BODYSTATE_ACTIVE_TAG, BODYSTATE_DISABLE_DEACTIVATION, BODYSTATE_DISABLE_SIMULATION,
@@ -161,6 +164,22 @@ class RigidBodyComponent extends Component {
     /** @private */
     _type = BODYTYPE_STATIC;
 
+    /**
+     * Whether the RigidBody component uses gravity.
+     *
+     * @type {boolean}
+     * @private
+     */
+    _useGravity = true;
+
+    /**
+     * The current gravity of this body.
+     *
+     * @type {null|Vec3}
+     * @private
+     */
+    _gravity = null;
+
     /**
      * Create a new RigidBodyComponent instance.
      *
@@ -572,6 +591,63 @@ class RigidBodyComponent extends Component {
         return this._type;
     }
 
+    /**
+     * Whether this rigid body should use gravity.
+     *
+     * @type {boolean}
+     */
+    set useGravity(value) {
+        if (!!value === this._useGravity) {
+            return;
+        }
+
+        Debug.assert(typeof Ammo !== 'undefined' && Ammo.btRigidBody.prototype.setFlags, 'pc.RigidBodyComponent.useGravity: Your version of ammo.js does not expose Ammo.btRigidBody#setFlags. Update it to latest.');
+
+        this._useGravity = !this._useGravity;
+
+        if (this._body) {
+            this._body.setFlags(this._useGravity && !this._gravity ? BODYFLAG_GRAVITY_WORLD_ENABLE : BODYFLAG_GRAVITY_WORLD_DISABLE);
+
+            if (this._useGravity) {
+                if (this._gravity) {
+                    _ammoVec1.setValue(this._gravity.x, this._gravity.y, this._gravity.z);
+                    this._body.setGravity(_ammoVec1);
+                } else {
+                    this._body.setGravity(this.system.dynamicsWorld.getGravity());
+                }
+            } else {
+                _ammoVec1.setValue(0, 0, 0);
+                this._body.setGravity(_ammoVec1);
+            }
+        }
+    }
+
+    get useGravity() {
+        return this._useGravity;
+    }
+
+    /**
+     * The gravity that affects this rigid body. Defaults to null to use world gravity.
+     *
+     * @type {Vec3}
+     */
+    set gravity(value) {
+        Debug.assert(typeof Ammo !== 'undefined' && Ammo.btRigidBody.prototype.setFlags, 'pc.RigidBodyComponent#gravity: Your version of ammo.js does not expose Ammo.btRigidBody#setFlags. Update it to latest.');
+
+        this._gravity = value;
+
+        if (this._body && this._useGravity) {
+            this._body.setFlags(BODYFLAG_GRAVITY_WORLD_DISABLE);
+
+            _ammoVec1.setValue(value.x, value.y, value.z);
+            this._body.setGravity(_ammoVec1);
+        }
+    }
+
+    get gravity() {
+        return this._gravity;
+    }
+
     /**
      * If the Entity has a Collision shape attached then create a rigid body using this shape. This
      * method destroys the existing body.
@@ -625,6 +701,17 @@ class RigidBodyComponent extends Component {
                 body.setActivationState(BODYSTATE_DISABLE_DEACTIVATION);
             }
 
+            if (this._useGravity && this._gravity) {
+                Debug.assert(Ammo.btRigidBody.prototype.setFlags, 'pc.RigidBodyComponent#createBody: Your version of ammo.js does not expose Ammo.btRigidBody#setFlags. Update it to latest.');
+                body.setFlags(BODYFLAG_GRAVITY_WORLD_DISABLE);
+
+                _ammoVec1.setValue(this._gravity.x, this._gravity.y, this._gravity.z);
+                body.setGravity(_ammoVec1);
+            } else if (!this._useGravity) {
+                Debug.assert(Ammo.btRigidBody.prototype.setFlags, 'pc.RigidBodyComponent#createBody: Your version of ammo.js does not expose Ammo.btRigidBody#setFlags. Update it to latest.');
+                body.setFlags(BODYFLAG_GRAVITY_WORLD_DISABLE);
+            }
+
             body.entity = entity;
 
             this.body = body;

src/framework/components/rigid-body/constants.js

@@ -35,6 +35,14 @@ export const BODYSTATE_WANTS_DEACTIVATION = 3;
 export const BODYSTATE_DISABLE_DEACTIVATION = 4;
 export const BODYSTATE_DISABLE_SIMULATION = 5;
 
+// Gravity flags
+export const BODYFLAG_GRAVITY_WORLD_ENABLE = 0;
+export const BODYFLAG_GRAVITY_WORLD_DISABLE = 1;
+export const BODYFLAG_GRAVITY_GYROSCOPIC_EXPLICIT = 2;
+export const BODYFLAG_GRAVITY_GYROSCOPIC_IMPLICIT_WORLD = 4;
+export const BODYFLAG_GRAVITY_GYROSCOPIC_IMPLICIT_BODY = 8;
+export const BODYFLAG_GRAVITY_GYROSCOPIC_ENABLE = BODYFLAG_GRAVITY_GYROSCOPIC_IMPLICIT_BODY;
+
 // groups
 export const BODYGROUP_NONE = 0;
 export const BODYGROUP_DEFAULT = 1;

src/framework/components/rigid-body/system.js

@@ -418,7 +418,9 @@ class RigidBodyComponentSystem extends ComponentSystem {
             'restitution',
             'type',
             'group',
-            'mask'
+            'mask',
+            'useGravity',
+            'gravity'
         ];
 
         for (const property of props) {
@@ -450,7 +452,9 @@ class RigidBodyComponentSystem extends ComponentSystem {
             restitution: rigidbody.restitution,
             type: rigidbody.type,
             group: rigidbody.group,
-            mask: rigidbody.mask
+            mask: rigidbody.mask,
+            useGravity: rigidbody.useGravity,
+            gravity: rigidbody.gravity
         };
 
         return this.addComponent(clone, data);