Init the data structures relevant for collision calculations when the…

… body is added, rather than on the fly

If a body is deleted before it can be the body0 of a collision, an
entry for it won't be created in the collisionKeys array. However, because
of the splice idiom used at removal, when a body that has no entry in
collisionKeys is deleted, an arbitrary entry will be deleted regardless.

Eventually, when further bodys are removed according to this pattern, there
may be no entry in collisionKeys at all, which will prevent the collisions map
from ever being emptied. This can completely prevent the firing of collisionstart
events.

src/drivers/ammo-driver.js

@@ -61,7 +61,11 @@ AmmoDriver.prototype.init = function(worldConfig) {
 /* @param {Ammo.btCollisionObject} body */
 AmmoDriver.prototype.addBody = function(body, group, mask) {
   this.physicsWorld.addRigidBody(body, group, mask);
-  this.els.set(Ammo.getPointer(body), body.el);
+  const bodyptr = Ammo.getPointer(body);
+  this.els.set(bodyptr, body.el);
+  this.collisions.set(bodyptr, []);
+  this.collisionKeys.push(bodyptr);
+  this.currentCollisions.set(bodyptr, new Set());
 };
 
 /* @param {Ammo.btCollisionObject} body */
@@ -103,10 +107,6 @@ AmmoDriver.prototype.step = function(deltaTime) {
     }
 
     if (collided) {
-      if (!this.collisions.has(body0ptr)) {
-        this.collisions.set(body0ptr, []);
-        this.collisionKeys.push(body0ptr);
-      }
       if (this.collisions.get(body0ptr).indexOf(body1ptr) === -1) {
         this.collisions.get(body0ptr).push(body1ptr);
         if (this.eventListeners.indexOf(body0ptr) !== -1) {
@@ -116,9 +116,6 @@ AmmoDriver.prototype.step = function(deltaTime) {
           this.els.get(body1ptr).emit("collidestart", { targetEl: this.els.get(body0ptr) });
         }
       }
-      if (!this.currentCollisions.has(body0ptr)) {
-        this.currentCollisions.set(body0ptr, new Set());
-      }
       this.currentCollisions.get(body0ptr).add(body1ptr);
     }
   }