Really. A replay camera would make this sim infinitely better. It quite hard to drive and view the physics at the same time as it is. This sim is really awesome. A replay camera would take awesome to the next level.
I'm wondering how someone does a crash, then has the same exact crash from different perspectives. is there a way to replay?
Certainly possible, but there would be a performance hit. You would need to be constantly recording the position of each node for every physics step (2000 per second). This existed in Rigs of Rods and there was a noticeable framerate hit. We would like to do it, but it is very far on the backlog and low priority.
Well, these physics do have something exploitable. Like any science, its observable-testable and more importantly its repeatable. F is always going to equal ma in newtonian physics. Because this is a simulation it is maths. If you use the same numbers in any process you get the same answer every time. That's the hallmark of a good simulation. So why not save a 'snapshot' of some initial conditions at the beginning of your replay and a timeline of ALL inputs by AI and player alike. Simply get the computer to re-run the simulation from some initial saved condition with a timeline of inputs to play out. That would be less data to save 2000 times per second anyway.
I've noticed that the game doesn't always behave exactly the same way every time. Maybe I was dealing with an edge case (it was a custom jbeam), or maybe respawns don't reset everything, etc. Whatever the cause, my input was constant and the result was not.
This is a good idea in theory, but there is one other variable you have forgotten. The framerate. Both physics step and FPS vary based on the speed of the PC, meaning if the game runs at a different FPS in the replay than in the initial crash, the results will be different. As for Gabe's "Noticeable framerate hit", it was only about a 15FPS difference. It could be a toggleable setting (a la RoR) so people with slow PC's could disable it. Additionally, it would mostly be for recording purposes, so playing the game at 20 FPS would be fine if you could re-watch what you did at 60, from many different camera angles.
