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by applfanboysbgon18 hours ago |
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upvoteby Jare10 hours ago|
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Mostly because determinism is an all or nothing proposition. Either EVERYTHING in game logic is perfectly deterministic and isolated from everything else, or it pretty much as if nothing was. So if you want to commit to determinism, you have to be constantly vigilant and debugging these maddening types of bugs. Whether this investment is worth it or not is up to each dev.

Sometimes you can find small areas of the game that can be deterministic and worth it. In a basketball game I worked on in the 90s, I designed the ball physics to be deterministic (running at 100hz). The moment the ball left the player hands it ran deterministically; we knew if it was going to hit the shot and if not, where the rebound would go to.

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upvoteby JoshTriplett17 hours ago|
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I think if it were as simple as "remember the RNG seed", game developers would do it every time. But determinism also means, for instance, running the physics engine at a deterministic timestep regardless of the frame rate, to avoid differences in accumulated error or collision detection. And that's something that needs designing in from day one.

Thank you for still prioritizing it.

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upvoteby magicalhippo17 hours ago|
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> running the physics engine at a deterministic timestep

As well as using special library versions of floating-point functions which don't behave the same across different processors I suppose, if you want to be safe.

Eg cr-libm[1] or more modern alternatives like core-math[2].

[1]: https://github.com/SixTrack/crlibm

[2]: https://core-math.gitlabpages.inria.fr/

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upvoteby 4 hours ago|
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upvoteby Krutonium17 hours ago|
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Tying physics to framerate at all is a mistake. Like, should be filed as a bug mistake.

There's no scenario in which that's desirable.

And yet even Rockstar gets it wrong. (GTA V has several framerate dependent bugs)

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upvoteby mrob16 hours ago|
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It's desirable for arcade games, which have fixed hardware including the display. There's no possibility of upgrading for better framerate, and the game can be designed so slowdown is rare or non-existent. Tying the physics to the framerate gives you very low and very consistent input latency with minimum developer effort.
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upvoteby Grimblewald2 hours ago|
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Right, all valid points, but consider the scale of a game like those coming out of rockstar. I'd understand for indie games and arcade games, but a single player rpg that will likely never be seen in arcade settings? Seems odd to me to see it here. Rockstar has the resources to do it properly, one would think, no?
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upvoteby JoshTriplett17 hours ago|
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I completely agree, but it's an easy mistake to make.
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upvoteby Keyframe17 hours ago|
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not framerate of rendering but physics running at (its own) fixed frame rate.
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upvoteby nottorp17 hours ago|
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Every game logic update, not only physics, should run on a timer that's fully independent from the frame rate.

The only place where that doesn't matter is fixed hardware - i.e. old generation consoles, before they started to make "pro" upgrades.

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upvoteby JoshTriplett8 hours ago|
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> i.e. old generation consoles, before they started to make "pro" upgrades.

And before it was realistically possible to port a game to run on multiple consoles without a complete rewrite.

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upvoteby bregma16 hours ago|
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I think you mean timestep. The video frames get updated on one timestep (the so-called "frame rate" because it is the rate at which video frames get redrawn, the inverse of its timestep), physics gets updated on a separate timestep, and gameplay or input or network polling can be updated on its own timestep.
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upvoteby Keyframe11 hours ago|
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pretty much, over the dozen or so game and rendering engines I made over the decades name mutated from tick to timestep to frame (rate) to refresh rate (hz) to tick again.. it doesn't matter as long as every system is decoupled and rendering is unbounded (if hardware/display combo supports it). This needs thinking from day one. Cool stuff you can do then is determinism, you can do independent timers which go forward, halt, backward in time, different speed multipliers over those (so some things run slower, faster, everything goes slower / faster), etc.
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upvoteby bob102918 hours ago|
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Determinism isn't essential to achieve record/playback experiences. You could just record the transform of the player at some fixed interval and then replay it with interpolation. This is arguably more "deterministic" in a strategic sense of shipping a viable product.
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upvoteby magicalhippo17 hours ago|
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The player is just one entity, you'd need to do the same to any other non-trivial entity. And you couldn't use fixed intervals and naive interpolation, otherwise you'd have entities clipping the ground when bouncing etc.
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upvoteby Cthulhu_17 hours ago|
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Probably (armchair HN reader, not a game developer here) due to dealing with multiplayer latency and / or performance / multithreading / scalability.
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