Why do game devs cap FPS?

[monster64]

Is there a reason for it? I know theres commands and stuff to get rid of it, but why do the devs do it in the first place? I mean in some games it wont matter too, much, like source (capped at 100 fps,) but doom 3, capped at 60??? What are devs thinking?

 

[Powermoloch]

Originally posted by: monster64
Is there a reason for it? I know theres commands and stuff to get rid of it, but why do the devs do it in the first place? I mean in some games it wont matter too, much, like source (capped at 100 fps,) but doom 3, capped at 60??? What are devs thinking?

No clue at all....

 

[cbehnken]

Originally posted by: monster64
Is there a reason for it? I know theres commands and stuff to get rid of it, but why do the devs do it in the first place? I mean in some games it wont matter too, much, like source (capped at 100 fps,) but doom 3, capped at 60??? What are devs thinking?

I think it has to due with timing events in the game. Not sure exactly why though...

 

[kylebisme]

Games are generally capped at one framerate or another simply to avoid wasting resources on more framerate than most anyone would ever even notice. With Doom3 the framerate is capped as 60fps because the whole engine designed to work on 1/60 of a second intervals. This is done to provide a more synchronous experience, where as other games use different frequencies for different aspects of the game. You can remove the cap on rendering in Doom3 as well, but that will throw it out of sync with the rest of the engine and causes problems with player movment and such.

 

[monster64]

Originally posted by: TheSnowman
Games are generally capped at one framerate or another simply to avoid wasting resources on more framerate than most anyone would ever even notice. With Doom3 the framerate is capped as 60fps because the whole engine designed to work on 1/60 of a second intervals. This is done to provide a more synchronous experience, where as other games use different frequencies for different aspects of the game. You can remove the cap on rendering in Doom3 as well, but that will throw it out of sync with the rest of the engine and causes problems with player movment and such.

But then wouldn't it also throw the game out of sync if someone playing doom3 got 40 fps maximum, if the game was designed at 1/60 of a second intervals?

 

[kylebisme]

Nah, it is much more complicated than that. There have been multiple articles on the subject, I don't know where to dig any up off hand but if you interested in learing more about how it works I am sure the information is out there.

 

[xtknight]

Originally posted by: monster64
But then wouldn't it also throw the game out of sync if someone playing doom3 got 40 fps maximum, if the game was designed at 1/60 of a second intervals?

Nope, 60 FPS is the maximum, it's not a set static rate that you must hit. The reason FPS is capped is because different subsystems (video, audio, network) work faster than others. For instance, your graphics card may be able to calculate a whole scene worth of video at 60 FPS, while your CPU can only calculate the physics for that scene at 40 FPS. The game will thus wait for the CPU while the video processing has already completed. Less efficiency already. Not to mention all this will cause your subsystems to go all out of sync. It doesn't make sense that that guy you shot off the balcony has his body all jerky falling down (~40 FPS) while the water in the scene is flowing at 60 FPS. With it synchronized at a 40 FPS cap, the body's animation is in sync with the flowing water. They architect the games with FPS caps in mind. Their physics better not be more advanced than their video, or else you risk your game suffering asynchronization. However, it's almost unnoticable if a body is falling at 40 FPS and your video is being updated at 60, so they don't worry about it too much. It definitely varies per situation, though. When physics processing is operating at a speed disadvantage, bodies that require more precision will look more jagged/out-of-sync than those which don't.

In Doom 3 particularly, the main reason they did it was to synchronize physics with video. On "trick jump" maps in games like Quake 2 and 3, people had to change their maxfps to perform different jumps because they all required a different physics rate. That got annoying.

Why 60 and not 80 FPS? Not certain, but most people consider that the "minimum playable rate", and others claim that's all your eyes can discern (not me). It's a good intermediary value (minimally playable but still no power being wasted).

 

[monster64]

Originally posted by: xtknight

Originally posted by: monster64
But then wouldn't it also throw the game out of sync if someone playing doom3 got 40 fps maximum, if the game was designed at 1/60 of a second intervals?

Nope, 60 FPS is the maximum, it's not a set static rate that you must hit. The reason FPS is capped is because different subsystems (video, audio, network) work faster than others. For instance, your graphics card may be able to calculate a whole scene worth of video at 60 FPS, while your CPU can only calculate the physics for that scene at 40 FPS. The game will thus wait for the CPU while the video processing has already completed. Less efficiency already. Not to mention all this will cause your subsystems to go all out of sync. It doesn't make sense that that guy you shot off the balcony has his body all jerky falling down (~40 FPS) while the water in the scene is flowing at 60 FPS. With it synchronized at a 40 FPS cap, the body's animation is in sync with the flowing water. They architect the games with FPS caps in mind. Their physics better not be more advanced than their video, or else you risk your game suffering asynchronization. However, it's almost unnoticable if a body is falling at 40 FPS and your video is being updated at 60, so they don't worry about it too much. It definitely varies per situation, though. When physics processing is operating at a speed disadvantage, bodies that require more precision will look more jagged/out-of-sync than those which don't.

In Doom 3 particularly, the main reason they did it was to synchronize physics with video. On "trick jump" maps in games like Quake 2 and 3, people had to change their maxfps to perform different jumps because they all required a different physics rate. That got annoying.

Why 60 and not 80 FPS? Not certain, but most people consider that the "minimum playable rate", and others claim that's all your eyes can discern (not me). It's a good intermediary value (minimally playable but still no power being wasted).

I see now, that makes sence, thx. Still, D3 is a bit low at 60. Source is fine at 100 though.

 

[RobFDB]

One of the reasons is fairness. Like xtknight said in Quake 2 and Quake 3 hardcore players use to butcher the games graphics to get the best performance they could. More FPS means you could make harder/longer jumps and so gave an unfair advantage to some people.

 

[kylebisme]

Originally posted by: monster64

I see now, that makes sence, thx. Still, D3 is a bit low at 60. Source is fine at 100 though.[/quote]
I can't say I have looked at Sorce's code, but I'd wadger that to mantian it's ablity to render at a high framerate it runs many parts of the engine at a 30hz or 20hz tick rate like many other games do including those on older Id engines. There are avantages to both methods, so which one is used comes down to a matter of personal preference.