Way back in the day, every game had its logic tied to its framerate – As anyone who’s ever tried to run an eighties PC game on a nineties PC only to see it run at 20x speed and completely unplayable can tell you.
But in the modern day this is less common. Generally the game keeps chugging along at the same pace, no matter how fast or slow the frames are being presented (unless, of course, everything is bogged down so hard that even the game logic is struggling)
And yet, you’ll still find a few. Any fan of Dark Souls who played on PC back when Prepare to Die edition first came to PC will remember how unlocking the framerate could cause collision bugs and send you into the void. And I recently watched a video of a gent who massively overclocked a Nintendo Switch OLED and got Tears of the Kingdom to run at 60FPS… Except everything was, indeed, running in fast-forward, rather than just being smoother.
This makes me wonder – Is there some unseen advantage to keeping game logic and framerate tied together? Perhaps something that only really shows on weaker hardware? Or is it just devs going “well the hardware we’re targeting won’t really go over this speed, and we don’t really give a fuck about anything else” and not bothering to implement it?
Game are still very much all functionally tied to framerates; it’s all just a matter of making that logic function the same across different hardware and framerates, generally calculated from frame times (we call it “delta time”).
Freya Holmér has a fantastic mathematical breakdown of one pretty common (and deceptively complicated) framerate-independent function: lerp smoothing.
If it is tied to frame rate, then a set of inputs results in a predictable set of outputs.
If not tied to frame rate, those same inputs have to be reproduced with the exact same time delay, which is almost impossible to do.
Sure, sub-millisecond time differences might not always lead to a different output. But it might.
Now, when is this determinism useful?
TAS (tool assisted Speedrun). You can’t tell the game: on frame 83740 press the A button. Given a list of inputs with their exact frames will always lead to the same Speedrun.
Testing. You can use methods just like TAS to test your game.
Reproducing bugs. If you record the game state and inputs of a player before the game crashes, you can reproduce the bug, which means that it will be a lot easier to find the cause and fix it.
Replays. Games like LoL, starcraft, clash of clans have a way to see replays of gameplay moments. If you save a video for each one of those, the storage costs will be prohibitively expensive. What they do instead is record every single action and save that. And when replaying, they run a simulation of the game with those recorded inputs. If the replaying is not deterministic, bugs may appear in the replay. For example if an attack that missed by one pixel in the game was inputted a millisecond earlier in the replay, it may hit instead. So it would not be a faithful replay. This is also why you can’t just “jump to minute 12 of the replay”, you can only run the simulation really fast until you get to minute 12.
I’m not a game developer so I don’t know if it is used for testing or reproducing bugs or replays. But I know it is used in TAS.
Of course, for this to be possible you also need your RNG function to be deterministic (in TAS). In the rest of scenarios you can just record what results the RNG gave and reproduce them.
