remove impostor from world after step to avoid cannon exception

src/Gamepads/Controllers/gearVRController.ts

@@ -73,7 +73,7 @@ export class GearVRController extends WebVRController {
     protected _handleButtonChange(buttonIdx: number, state: ExtendedGamepadButton, changes: GamepadButtonChanges) {
         if (buttonIdx < this._buttonIndexToObservableNameMap.length) {
             const observableName: string = this._buttonIndexToObservableNameMap[buttonIdx];
-            
+
             // Only emit events for buttons that we know how to map from index to observable
             let observable = (<any>this)[observableName];
             if (observable) {

src/Physics/Plugins/cannonJSPlugin.ts

@@ -21,6 +21,7 @@ export class CannonJSPlugin implements IPhysicsEnginePlugin {
     private _fixedTimeStep: number = 1 / 60;
     private _cannonRaycastResult: any;
     private _raycastResult: PhysicsRaycastResult;
+    private _removeAfterStep = new Array<PhysicsImpostor>();
     //See https://github.com/schteppe/CANNON.js/blob/gh-pages/demos/collisionFilter.html
     public BJSCANNON: any;
 
@@ -54,6 +55,12 @@ export class CannonJSPlugin implements IPhysicsEnginePlugin {
 
     public executeStep(delta: number): void {
         this.world.step(this._fixedTimeStep, this._useDeltaForWorldStep ? delta : 0, 3);
+        if (this._removeAfterStep.length > 0) {
+            this._removeAfterStep.forEach((impostor) => {
+                this.world.remove(impostor.physicsBody);
+            });
+            this._removeAfterStep = [];
+        }
     }
 
     public applyImpulse(impostor: PhysicsImpostor, force: Vector3, contactPoint: Vector3) {
@@ -165,7 +172,9 @@ export class CannonJSPlugin implements IPhysicsEnginePlugin {
         impostor.physicsBody.removeEventListener("collide", impostor.onCollide);
         this.world.removeEventListener("preStep", impostor.beforeStep);
         this.world.removeEventListener("postStep", impostor.afterStep);
-        this.world.remove(impostor.physicsBody);
+
+        // Only remove the physics body after the physics step to avoid disrupting cannon's internal state
+        this._removeAfterStep.push(impostor);
     }
 
     public generateJoint(impostorJoint: PhysicsImpostorJoint) {

src/Physics/physicsEngine.ts

@@ -117,8 +117,7 @@ export class PhysicsEngine implements IPhysicsEngine {
             var removed = this._impostors.splice(index, 1);
             //Is it needed?
             if (removed.length) {
-                //this will also remove it from the world.
-                removed[0].physicsBody = null;
+                this.getPhysicsPlugin().removePhysicsBody(impostor);
             }
         }
     }

what's new.md

@@ -193,7 +193,7 @@
 - Fixed issue where VRExperienceHelper.onExitingVR observable was being fired twice ([atulyar](https://github.com/atulyar))
 - Avoid firing onExitingVR observable multiple times when calling exitVR() and add observables to Viewer that can be used instead of the ones in VRExperienceHelper ([atulyar](https://github.com/atulyar))
 - GizmoManager should hide existing gizmos if a non-attachable mesh is selected ([TrevorDev](https://github.com/TrevorDev))
-- Ignore isPickable = false for vr ray casting if the mesh's name matches the specified floorMeshName to maintain backwards compatability ([TrevorDev](https://github.com/TrevorDev))
+- Ignore isPickable = false for vr ray casting if the mesh's name matches the specified floorMeshName to maintain backwards compatibility ([TrevorDev](https://github.com/TrevorDev))
 - Fix File Loading if hosted from `file:`-Protocol ([ltetzlaff](https://github.com/ltetzlaff))
 - Do not throw error when updating a controller with no left stick ([TrevorDev](https://github.com/TrevorDev))
 - Exiting VR can result in messed up view ([TrevorDev](https://github.com/TrevorDev))
@@ -206,6 +206,7 @@
 - Sometimes duplicate controller models are loaded in VR ([TrevorDev](https://github.com/TrevorDev))
 - Particle emit rate and start size over time do not reset on every particle system start ([TrevorDev](https://github.com/TrevorDev))
 - SSAO2 now correctly takes diffuse texture alpha value into account. ([CraigFeldspar](https://github.com/CraigFeldspar))
+- Avoid exception when removing impostor during cannon world step ([TrevorDev](https://github.com/TrevorDev))
 
 ### Core Engine
 
@@ -236,7 +237,7 @@
 - Animation navbar now updates correctly when a new model is loaded ([RaananW](https://github.com/RaananW))
 - Non-normalized meshes didn't center and focus correctly ([RaananW](https://github.com/RaananW))
 - Meshes with skeletons could have incorrect animations ([RaananW](https://github.com/RaananW))
-- Removed element IDs from viewer's templates to allow muitiple viewers in a single page ([RaananW](https://github.com/RaananW))
+- Removed element IDs from viewer's templates to allow multiple viewers in a single page ([RaananW](https://github.com/RaananW))
 - Viewer is not using Engine.LastCreatedScene anymore, to support multiple viewers in a single page ([RaananW](https://github.com/RaananW))
 - Template location was ignored if html was defined ([RaananW](https://github.com/RaananW))
 - Drag and Drop only worked if a model was already loaded before ([RaananW](https://github.com/RaananW))