Is Slowdown just a framerate drop?

Discussion in 'Console Technology' started by Goodtwin, Oct 15, 2014.

  1. Goodtwin

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    In some games, you can see the game turn into a slide show, but the gameplay seems to still be running at full speed. Then there are other games where the gameplay actually starts to play in slow motion. My question is this, is game slow down really just a severe drop in framerate, or is slow down something different?
     
  2. TomRL

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    I've noticed that in some games, when I look toward an empty area, it's really smooth, but when I move the camera across a city, there is some sort of slowdown. And this is when I know for certain it's a solid 30. So yeah, I ask this question too.
     
  3. Infinisearch

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  4. Shifty Geezer

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    You can think of the game as made of two parts - the underlying virtual world where things happen, and the image showing those results on screen. These are usual decoupled these days. Now both need to complete one cycle within 1/30 of a second for smooth 30 fps visuals. If the world simulation completes in time but the drawing takes longer, you get a constant game speed but a slower framerate (slideshow). If the world simulation itself slows down, it either slows the game down (very old school) or progresses in larger time steps resulting in juddery motion no matter what speed your framerate is. Consider a car game where it takes 1/5th of a second to calculate the Awesome Physics, and draws the results with PS1 level graphics. It can draw the game at 2000 fps on a PC, but the changes in the world are only updated 5 times a second, resulting in a slideshow.

    A well written game will have both these decoupled and use a world simulation timestep that's either constant or can accommodate changes in simulation speed, such as updating the physics at less than framerate and interpolating positions based on elapsed time. There's very little cause for actual game slowdown like we used to have on the 8 bit machines. I'm curious what games you've seen this on.
     
  5. Goodtwin

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    Hyrule Warriors, and from what I have read, its common with the Warrior games in general, across all platforms. The game never looks like a slide show, but the action when blasting lots of enemies can cause the game to slow to a crawl. Its very different from the typical framerate dips I have experienced in other games. Its not just Hyrule Warriors though, I have played plent of games over the last 20 years that have slowdown. Heck, Street Fighter 2 was notorious for it back on the SNES. Pretty much all the 3D Zelda games experience it at times when consecutively hitting tons of enemies with a spin attack.
     
  6. TomRL

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    I think this may have happened in MGS3 if anyone has played it. In the latter half, during Grozny Grad, there were a lot of enemies around and if something exploded the game would slow down, but it didn't seen to be dropping frames. It kind of looked like slow motion.
     
  7. HTupolev

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    People sometimes prefer slowing down the simulation over variable time deltas.
     
  8. Nesh

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    ZOE2 comes to mind (PS2 version)
     
  9. orangpelupa

    orangpelupa Elite Bug Hunter
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    yups, PS2 games have those. some of their games slow down some other frame drops. Personally i prefer slow down than frame drops.

    it feels make the scene more "epic". But the epicness got blown away when the slow-down goes too bad and the audio become garbled.
     
  10. Goodtwin

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    I agree with certain games. I was just curious as to what really causes the slowdown, because it really did feel like it was different than just severe framerate drops. So basically, most games are have the rendering part of their game running slower than their physics engine, but it seems that some games hit severe bottlenecks in their physics engine at times, and that's what causes the slowdown. You could have a 30fps game stick to the 30fps refresh, but with the gameplay slowing down. Thanks for the input fellas, I had always been curious about slow down in games.
     
  11. Shifty Geezer

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    Looking at Hyrule Warriors, that definitely looks the case. With so many enemies, there'll be 'physics' spikes in the calculations where each frame of physics takes longer than a frame of display, so it has to take two frames to draw the updates. Once past the longer processing parts, it snaps back to normal.
     
  12. AlBran

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    Ninja Gaiden 2 Ch. 10 <3

    ...pre-patch. :cry:

    --

    IIRC, same thing happened in Painkiller with low framerates.

    Injustice does it as well, but I've only noticed it on PC with the shadows set to maximum, tanking the framerate (kind of a pointless setting considering the shadows don't look any better in practise).

    ---

    There's com_fixedtic in Doom 3 to mess around with too.
     
  13. Goodtwin

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    I guess my other question is, would this physics/game logic slowdown show up as a reduced framerate in a DF framerate test? I am assuming it would still show the 30fps, but the game just runs slower until it catches up.
     
  14. Shifty Geezer

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    Yes. DF would see duplicate frames and count them as FPS. DF doesn't differentiate between the causes of lower framerates, whether rendering or game physics, and it doesn't make a difference really. Although I'm certain if they came across a physics slowdown in any game they tackle, they'll report it, because it's extremely rare these days. TBH I'm not surprised it's Nintendo showing the problem in this day and age - it's suitably retro an approach for them. ;) Any and every game dev is well informed about decoupled physics and rendering, and delta times for smooth updates. The major middlewares handle a lot of this pretty transparently too.

    Edit - is the slowdown smooth on Wii U, or does it notably drop frames? Rendering could still be decoupled an tweened for delta time. That'd show as 60fps, and rightly so, even though the game physics drops to 30 fps.
     
  15. Goodtwin

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    Hyrule Warriors runs at 30fps, not 60fps. Yes, the slowdown is smooth, it doesn't look like a slideshow at all when it happens, but the game runs in slow motion. Keep in mind that Tecmo Koei developed Hyrule Warriors, not Nintendo. I cant say for certain that the framerate isn't dropping, because when running in slow motion, your not able to pan the camera fast enough to give the slide show look. When the character animations are running so slow, a slow framerate might not look like a slide show, since the character animations and panning of the camera have been slowed down to a crawl.
     
  16. function

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    What if it's that normally the game is running too fast?
     
  17. Goodtwin

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    Apparently this is the route that Tecmo goes with their Warriors game engine. So when the physics simulation load spikes, it just simulates less time per frame until it catches back up, which on screen looks like its playing in slow motion, and it essentially is. For that 2-3 seconds, there was far less time simulated in the games virtual world. Its been a bit diffiucult for a novice techie like myself to really make senses of all this time time step info, and how it applies to games. From what I can decipher, it sees that the majority of games physics engine run far quicker than the games rendering speed, so you could have the game simuilation updating 240 times per second, while your rendering framerate is only 60fps.
     
  18. Shifty Geezer

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    I doubt most games run the physics higher than 60 fps a second. Only racers advertise that. At 60 fps, physics is completely smooth for a 60 fps output. The important point is physics will be at 60 fps (or whatever. Lower for some content) even when the framerate fluctuates all over the shop. That means object movements are consistent and the rendering is just catching slices of action as often as the renderer can.

    Is that a dev quote?
     
  19. Goodtwin

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    That's what I was reading as well, that most of the time, the physic engine runs at a lower framerate than the rendering framerate, but that's not always the case, such as Shin'ens Art of Balance, it renders at 60fps, but the physics engine is running at 240fps. So they are running the physics loop three times for every drawn frame. This give very accurate physics, but doesn't come free. This is a simple puzzle game, so they have the CPU resources available to run this many steps per frame, but to do this in a 3d world such as a plat former or shooter could quickly become a CPU resource hog. So the majority of games will run physics updates far less often than the rendering updates. They can also break things down so that certain aspects are updating more frequently, and then perhaps objects that are far out of reach, are updated far less often.
     
  20. Shifty Geezer

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    Have had an interesting experience with Diablo3 on PS3. A couple of times when it's got busy, it's suddenly accelerated when things calmed down. The slowdown wasn't particularly noticeable (framerate drop was). The curious thing is the snap-back regards time. This is offline. I don't recall that in any other game. Usually you'd just have the physics return to normal time.
     
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