While participating in a league race, there was noticeable “invisible” collisions occurring. The race was cancelled, and the following test run was acted out to get some footage of things happening. The following video was taken on April 14th, 2023. The video was filmed in this game.
At 0:11, my car was hit to the left randomly, then hit back to the right.
At 0:22, my car hits the car infront of me a few studs before the car actually should’ve made contact.
At 0:51, my car is dragged into the corner by the yellow car infront of me, even though it’s far infront of me.
At 0:54, my car then hits the yellow car, even though it’s very far infront of me.
At 1:21, when the white car hits me on his screen [shown top left] his car goes spinning wildly out of control.
Expected behavior
The behavior shown throughout the video is not how our cars have been acting on the platform for the past 10 years. Usually whatever you see on your screen, is what you hit, however now we are hitting things that aren’t even there. The issue seems to correlate similar timing to this bug which also relates to strange physics, however their physics issues are coordinated with humanoids so I can’t be sure this is the same issue.
It was like this in the past as well, but it has only gotten worse.
Summary
Replication and physics have always been janky by themselves. When put together you get awful delays. You can literally crash into other people’s cars by running into them on your screen, which might be 90 studs away on the other person’s. It all comes down to ping.
Since I have an average ping of 100ms, I’m often the one who receives the most pain in replicated physics.
These issues have only gotten worse with the additions of PGS and various physics updates.
So, I’d believe this issue depends on ping. Though, there was noticeable issues that have occurred recently involving animations and physics with animations as stated in this report.
It’s likely that the fix of this bug report linked below is what caused these issues because they both have matching timeframes and relate to replicated physics:
I’ve seen this issue in numerous live games. Seems to happen on both settings for adaptive timestepping.
Why does it look like the other player’s cars are jumping back and forth? Is it some custom replication or lag-compensation side-effect?
It could be that on some physics frames they are further back than they should be, and since 1 rendered frame has 3 invisible physics frames, it may look like they are colliding with nothing.
I’m familiar with Vision Lag, due to the lack of predictive pathing. This however is a fundamental difference. Usually you only hit what you see on your screen. Now we are hitting things that, simply put, aren’t there.
I’m wondering if this bug is still happening at this time? The offending change that was causing the issue with humanoids was reverted. When did you first notice the issue?
I’m aware of predictive pathing, but the physics collisions are further delayed even after the part has hit on both clients and the server. This has been the case since PGS and is more noticeable on slower servers and networking.
I’m unsure why this happens though. When I move my character and another character is standing, I’ll collide with them. When someone else moves their character into mine, I’ll collide with them, but they don’t collide with me.
Looks like it might be fixed. Hard to say for sure, but I’ve spent some testing laps behind some folks, and the collisions appear to be back to normal. [The normal “vision lag” deal.] Someone noted they thought it was occurring on April 8th during an event, but it was definitely occurring on April 14th [that’s when the footage from the video in my OP was from]
The mesh featured on these cars are a special mesh object inside a brick [like that of a hat accessory], and we have a hit box made of regular Parts [blocks] with the tires being a ball with a specialmesh inside it to make it look like a tire.
