Client Side Prediction - PhysX Resimulation Hack

Not sure what the gotchas are yet, but I figured out a way to make FixedUpdate run x number of times between Updates. Useful for fast forwarding the simulation or client side prediction. Just call this first part:

int count = 0;
int resimFrames = 456;//number of frames you want to resimulate or fast forward
Time.captureFramerate = 1;
Time.timeScale = resimFrames / (1f / Time.fixedDeltaTime);
WaitForFixedUpdate wait = new WaitForFixedUpdate();

while(count < resimFrames)
{
count++;
yield return wait;
}

Time.captureFramerate = 0;
Time.timeScale = 1;

It'd be nice if unity let us step physics manually, but maybe this will work in the meantime. I've got it working in a basic scene doing some client side prediction and it seems to work pretty good.

 

Hi, I'm stuck in here, is that any artifact comes with this hack?

BTW there're some rumors said resimulation will comes true in 2016, and PhysX will be upgrade to the latest version in 5.5, I'm not sure will resimulation comes at that time though.

 

Not that I'm aware of but you'd have to tell everything to stop while you resimulate. Depending on your game this could be a huge PITA

The collisions in my game are just sphere/sphere so so I ended up not using this method and writing my own collision code. Hopefully Unity adds resimulation.

 

Hi @nocanwin Can you provide an actual script that you made this happen with. I'd like to see what you did.

 

Sorry, I'm not sure what you're asking for @DRRosen3. I've adjusted the initial code so you can throw it into a coroutine and it should work. If you're asking how I would use it for client side prediction then that is a much more complex issue. Running the resimulation is only a small part of it. Again, I ended up not using the hack so I'm not sure what all the pitfalls are.

 

Oh so this isn't actually a working concept (yet)?

 

I'm not sure what you mean? Concept for what? The code is dead simple and it works.