[pfisch]

No I am just being realistic as an actual game developer. This is not a conceptual discussion. It doesn't make any sense to implement this change because if your fixed timestep for the physics system is breaking down then gravity not calculating correctly is the least of your problems. The controls would be unresponsive if the dt became large anyway. You are talking about more than doubling the number of operations for all acceleration based movement which is just about every movement and applied force in the game. If you thought the framerate was hurting before because too many objects were on screen doubling the physics calculations is not going to help you out. It might not hurt that bad but it really depends, you would need to profile it. It doesn't matter though because the tunneling would be another bigger issue that you would also have to address for this to even matter, and that would definitely hurt bad to check for.

During the far majority of use cases the timestep is fine, and you are just creating deadweight by doing this. Plus I guess you are now doing tunneling checks as well to create further deadweight for the rare occasion when someone has framerate issues.

I am looking at this in the sense that I would actually implement this in a game I make, and I would not because the upside of doing this is basically "if the game is already fucked I want it to be maybe not as fucked but still having many other big issues with pretty much every other component of the game logic", vs a bunch of deadweight when the game is running correctly, which should be 99.5% of use cases.

Am I adding assumptions here? I guess so but they are real ones for real game developers. Unless you are doing something very unusual these would be your concerns.

This is not an academic exercise for me like it maybe is for you and most of the commenters it seems like.

[jQueryIsAwesome]

> the game is unplayably choppy anyway so it doesn't even matter.

My point originally was about this statement of yours, that is purely conceptual and you skew the discussion to address the other part of your comment (or you through that was the point but didn't explain so in your answers)

But anyway, one assumption is that every game should have a fixed gamestep, in many single player games (real single player games) you don't want to do that, because is preferable that the user can see the ball coming to the player than to magically appear behind the player even if that is "timely correct"; the ball/interface going slow is a lot less frustrating that losing without realizing why. Platformers for PC with (virtual) high speed movements come to mind as a common example of this.

Even multiplayer games suffer of this; in most online FPS if the server suddenly slows down all the players start experiencing lag and everyone looks like they are "teleporting"; with a not-fixed-timestep you could slow everyone down so the problem becomes a lot less frustrating because the player still have complete control and understanding of their in-game character; just a bit slow-mo until the server speeds up to normal. The teleporting should be used only to sync with the server when the client connection is the one with problems updating.

[pfisch]

Oh well unplayably choppy is more subjective but I was going with the true problems a large dt would create like collision detection failure and controls not working.

I can't think of a framework that doesn't have a fixed timestep except for maybe gamemaker or some of the simpler frameworks. Maybe some of the html5 stuff is non-fixed timestep but that is a field that is just coming into its own right now.

None of the bigger 2d or 3d physics engines today that I know of use a non-fixed timestep.

In platformers with high speed movements fixed timesteps are even more important because of tunneling. You can often account for tunneling in some of the better physics engines but it is sloooow.

In fps games there is a lot of interpolation going on with the server correcting player and object positions. If the server lags you and everything else is going to teleport no matter what. The server is not even accepting your control input at that point so either you are going to desync or you are going to teleport when the server tells you your real position. Generally in fps games only critical physics objects are being server corrected anyway, this is usually a small fraction of the physics objects. For example if an enemy fires a rocket at you that is not usually server corrected. If you get hit in the server calculations then you got hit whether or not you think you dodged it client side.

My point is that if the server hiccups your jump being slightly off is not the big problem, The big problem is that the controls are unresponsive. Also when the server hiccups it is rarely the actual fixed timestep serverside that is your problem, it is the internet. If your computer hiccups then it is not updating positions from the server so all critical objects are going to teleport. Could there maybe be slightly less teleporting on non-player controlled critical physics objects? Maybe so but if you are losing that many timesteps than things are going to jump around on your screen no matter what because your framerate is like 5.

[stcredzero]

> in most online FPS if the server suddenly slows down all the players start experiencing lag and everyone looks like they are "teleporting"

Why would server lag effect FPS? I can only see how it would effect the reported positions of the other players because you aren't getting updates to changes in their movement. Server lag should never effect your FPS.

[rmk2]

FPS means First Person Shooter here, I reckon.