Hi there,
Each event E_UPDATE is triggered before the update of the scene, right ?, which causes the update of the physical component by firing E_PHYSICSPRE / POSTSTEP.

However it seems that physical events are triggered before. In the example of the vehicle, I put fprintf to see the order and I got the following


I also put in the example initialization
PhysicsWorld * pw = scene _-> CreateComponent ();
pw-> SetFps (30.0f);
pw-> SetInterpolation (false);
engine _-> SetMaxFps (30.0f)

I’m probably missing something, some clue?

Physics is updated via the E_SCENESUBSYSTEMUPDATE message that is sent by the scene from it’s E_UPDATE handler. When physics needs to tick it’ll send E_PHYSICSPRESTEP which does double-duty as the fixed update message.

So depending on your event subscription sequence what you’re seeing there makes sense. That’s handled through Bullet’s internal-tick callback. It sounds like cludge but it does mean that whenever you have a fixed-update fire that you’ll also have an actual physics-sim frame and not an interpolation - which is pretty important to any logic you have, it’s a win and a subtle nicety.

The sequence of events can be seen in Scene::Update.

So this comment in the sample
// Subscribe to Update event for setting the vehicle controls before physics simulation
means “before next physics simulation”, which could be in the next frame?

Can you tell me which sample so I don’t go off explaining the wrong thing?

means “before next physics simulation”, which could be in the next frame?

Assuming that’s a script/logic-component/etc then sort of but no, that will be right before physics and fixed-update for the frame currently in flight, not the next-frame - really depends on how you mean next.

Although in Scripts and LogicComponent it’s referred to as update it’s actually the E_SCENEUPDATE event they use for that, which is also sent by the Scene from Scene::Update.

Update should always be sent before fixed-update which should always be sent before physics does anything.

That’s what I thought when I asked. The example is 46_RaycastVehicle
This is how I subscribe to events

raycastvehicledemo.beginframe E_BEGINFRAME
vehicle.fixedupdate LogicComponent FixedUpdate (E_PHYSICSPRESTEP)
raycastvehicledemo.physicsprestep E_PHYSICSPRESTEP
raycastvehicledemo.update E_UPDATE
raycastvehicledemo.endframe E_ENDFRAME

I thought the flow should have been

raycastvehicledemo.beginframe E_BEGINFRAME
raycastvehicledemo.update E_UPDATE
vehicle.fixedupdate LogicComponent FixedUpdate (E_PHYSICSPRESTEP)
raycastvehicledemo.physicsprestep E_PHYSICSPRESTEP
raycastvehicledemo.endframe E_ENDFRAME

Yeah, that’s my bad.

E_UPDATE is a grab-bag event and will almost always come after physics-update (it depends on subscription/scene-creation sequence), that sample probably shouldn’t be subscribing to it.

E_SCENEUPDATE is the one that is guaranteed to occur before physics. E_UPDATE could happen in any order.

Edit: there’s probably a ton of code that is subscribing to that but really shouldn’t be, even in the core-engine. IIRC the scene-events didn’t exist at one point in the past.

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Thanks for helping me