Send all current PhysicsWorld.triggerBeginEvents and PhysicsWorld.triggerEndEvents where either of the PhysicsShape involved are valid (see PhysicsShape.isValid) and have a callback target assigned (see PhysicsShape.callbackTarget). These events will only be created if one of the shape pairs has PhysicsShape.triggerEvents set to true. Only callback targets that implement ITriggerCallback will be called. This is called automatically every simulation step. This must be called on the main thread.