2D Vehicles

Let's not forget Dr. Brian Beckman's The Physics of Racing Series, at the time he was a researcher working at Microsoft on the Forza video game series.

https://www.youtube.com/watch?v=I8GQCZgCNw8

I built an OpenGL car physics simulation as an undergrad as a project (pre-Claude). It was very fun.

Pretty cool to click the link and find it has been bookmarked for a decade on my end :-)

The diagrams seem to have been written (or generated[1]) while looking at the project source code, and use the sort of bass-ackwards approach to code documentation of giving a “post-hoc summation” that only makes sense when you’ve already read the code, rather than serving as an introduction to the code for someone who hasn’t read it yet.

That being said, AFAICT, the diagrams are also basically irrelevant to the article in its capacity as a high-level overview of the project. You can just ignore them for the purpose of reading the article.

It’s when digging into the project source code that you should look at those diagrams, and then feel frustrated by how much they suck. :)

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[1] This seems to happen a lot with LLM-generated code docs / diagrams / etc, when the docs are written in the same session as the code itself, but later; the LLM seems to see the docs as “following” the prior work in its linear context, and so mistakenly writes as if the reader of the docs will have also read whatever’s in the context before getting to the docs. That assumption, of an incrementally-growing shared context that can be implicitly made reference to by “later” text to compress that “later” text, makes a lot of sense when generating one long linear stream of prose, or even when generating a series of chain-linked entries (like conversation responses, or chapters of a book); but doesn’t work out when generating a web/graph of separate bits of text. This is kind of a fundamental flaw in producing coding agents as fine-tunes over conversational base models, and it’s one that coding-agent harnesses have yet to really focus on addressing.

What in particular would you like to know?

As I said in the summary article, the core is a "textbook" 2D rigid body simulation (the "Brick" layer), and the Car bit is mostly a matter of deciding what forces are applied to the tyres.

In short, the tires "like" to go back and forward, but resist going sideways (relative to the direction they are pointing in).

The forces which are applied at the tyres are roughly equivalent to friction, but not quite (friction is stranger than many people think, and is not actually very velocity dependent). In some ways my tyre forces actually behave more like a form of "viscous drag" actually. I knew this was a bit dodgy at the time, and it was a sort of conscious "hack" that was chosen to produce "playable" behaviour as simply as I could.

Yes, without really solid direction, agents will produce absolutely impenetrable diagrams. "The single biggest problem in communication is the illusion that it has taken place."

Losing control of the vehicle in birds-eye view felt closer to reaching my human limits than reaching the vehicle limits, I really missed that with the change to 3D. The whole city also truly felt like it was designed around the birds-eye view, like the group of Hare Krishna (GTA I) or Elvis impersonators (GTA II) behaving like virtual ants when rushing into them was always something magical and wasn't quite the same in 3D.

I still remember GTA 2 had the best radio

Laughing vampires dance!

Thanks. I'm glad you got something out of it.

Cool project. Have you tried to implement articulating drawbar trailers[1]? The ones where the first axle of the trailer is fixed to the drawbar, making the front wheels turn when the drawbar moves. They seem to be much more common in Europe than in the US. In my experience, these are much harder to back up than fixed axle trailers.

[1]: https://www.pacton.nl/en/products/drawbar-trailer/drawbar-tr...

The visualization of potential results is quite mesmerizing.

That was a lot of fun to play with.

I think the fractal solver is bugged, but maybe I am just using it wrong. It says placing a cone in the red zone will block the vehicle, but either the colors are inverted or the backend is off, because everything is red except a few spots.

Otherwise very fun. I managed to park a truck the solver called impossible :)

Note: Using safari on an iPad of that matters.

This is pretty fun!

Is it actually solving anything though? It always seems to get stuck with the semi half sticking out.

There was a demo of a remake in progress on the Archimedes which did the rounds back in the 90s which was also amazing https://www.youtube.com/watch?v=jssOIpGYH3E which was the first game I saw do real time anti aliased line rendering for the ship-ball connection.

GTA didn't exist back then, so I had to learn them from the lore.

And shortly afterwards, in addition to all the different physics-in-action experience, I learned about how car insurance excess works.

I knew about tires prices and cable wear on non hydraulic handbrakes so I really only played with the scandinavian flick or the handbrake on snowy days.

You're very welcome.

I made a parking simulator a long time ago. To make it realistic, you have to take into account that each wheel turns at a different angle. Both turning wheels need to turn at an angle that meets in the same point of a line that comes out of the back wheels. And, at low speed and acceleration, there is no drifting. To determine how the car moves, since all the wheels point to the same intersection point, just do angular movement of the car pivoting on that point, making angle * radious of the center of the drive wheels match the speed of the car. Wheel differential compensates for choosing the center of the wheels.

That's an interesting problem, and I can't immediately see why you would keep getting a side-effect like that.

Good luck with figuring it out!

I just sunk an hour into this. I'm feeling better already.

omg yes thats awesome, please add save-game functionality i wanna play more later but i have to go touch grass

Where can I look at the source?

I'd like to see the code that goes with the diagrams.

I'm into go karts and they turn on three wheels because they are a solid rear axle, and the front wheels have a lot of caster. Is live to try to model that.

There are various games that do this pretty well. For example: https://store.steampowered.com/app/4265570/Parking_in_Tight_...

It's probably not a realistic enough simulation to be a viable learning aid, but that's a funny idea.

I might build something else on top of this though, and will try to keep parking in mind!

Thanks. I'm glad you liked it.

There isn't much "air resistance" (or general velocity dampening) on these things, and the velocities carry over when you change the body's "shell".

So, it's sort of intended, but also not very significant one way or the other.

Correction, it was some mildly ChatGPT-assisted PatSlop.

I speak with some authority on the matter. ;-)

Maybe I'll make one, if I get time, and am not distracted by other things.

The original was very similar, but with minimum UI (no "Settings" panel), and it was just black on white line drawings, although I did add skid trails etc. after I'd got the core of it working.

Learn from the old master... with a big stinkin' LLM interposed!

Why needlessly do extra work when it's easier than ever before to modernize what is already made? Why would he want to be a vanguard for "hand coding"?

I've been a developer for not nearly as long as the author but long enough that at some point it felt like I was writing the same code and same abstractions over and over again and sometimes a new novel problem would reinvigorate my love of programming but today I'm happy to let an LLM write the tedious code while I give the more fun high level architectural direction and when reviewing the code sometimes I'll give it a nudge in a different direction. I suspect the author has written code like the 2d car physics many times over. Just my 2 cents.