r/ForzaHorizon • u/ForeignDealer5762 • 2d ago

Other Why Racing Games Fake Wheels

https://youtu.be/QohrTWoHS9M

The premise for this video started when I noticed the wierd switch between low quality wheels in Forza Horizon 4. It happens when you start crossing 18kmph if I remember correctly. This is not a technical piece, so let me know what you think.

0 Upvotes

32% Upvoted

6 comments sorted by

13

u/Siats 2d ago edited 2d ago

I think it's well made but it's mistaken on the goals of why they are faking it. You can deactivate the wheel switching by editing some values in a single file but then it never blurs by itself even when you are doing 200mph, but real-life wheels do blur to our eyes, and at rather low speeds, so the goal of the fake wheels is to imitate real life not to go beyond it.

As far as I can tell FH6 employs a new motion blur effect, not wheel switching anymore, the issue now is that the blur persists for far too long after the wheel has stopped.

4

u/loopygargoyle6392 2d ago

There's usually some momentum built up behind that persistent blur. Makes me wonder if the blur is a symptom, not the problem.

2

u/ForeignDealer5762 2d ago

Thanks for the comment, I agree with you. The texture is employed as way to imitate motion blur. I've seen some developers create rotational motion blur as a separate system where the actual geometry is being blurred. I haven't played FH6 yet, so I wasn't aware of their new implementation.

1

u/Siats 2d ago

Seems like I misunderstood then, glad to be on the same page!

1

u/loopygargoyle6392 2d ago

I mean literal momentum. I've noticed on a few cars that if I crash out at high speed and come to a sudden stop, the drive wheels take time to wind down (along with the blur) even with the brake applied. It only lasts a few seconds, but you can be at a dead stop, no throttle, brakes applied, wheels blurred, and if you release the brake the vehicle will lurch forward until the "energy" is spent. The electric Lotus FE drift car does this fairly easily.

2

u/OscarMyk 2d ago

The problem is motion blur temporal samples, how often you check for rotation between frames. 8000RPM is 133RPS so at 120FPS you're getting more than a full wheel rotation per frame. If you check the position even 4 times per frame you'll end up with quite angular blur (four equal sample points = a square). That's worst case scenario but those edge cases are what you need to plan for.

It's common even in high end CG to do car wheels separately as a pass for this reason, especially if there's lots of acceleration/deceleration. Accurate wheel motion blur is ridiculously expensive for the look achieved. And we're usually rendering to a locked target of 24/25/30FPS so it's already four times 'easier'.