possible jumping related bug

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D-FENS
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possible jumping related bug

Post by D-FENS » Tue Jul 18, 2017 2:39 am

Discovered what appears to be a client side bug when jumping between team islands on the Island Hopping map.

I used to be able to make the long jump over the lighthouse and land on flat ground when jumping from one corner team island to opposite corner team island. Now there's a few ppl experiencing the issue of landing on the side of the island, not quite making it all the way to flat land.

Every now and then this also affects the short jumps from one island to another, at least for myself.

I get the same results with fully updated Win7 running the 2.4.10 client and fully updated Linux Mint 18.2 running the 2.4.11 client, on a dual boot system, ie, no vm's are used.

Gnu-sense set tankspeed to 39 (default is 35 on that map or at least that's where it was when we tested) and we were both able to make the complete jump. Set at 35, neither of us could. Someone else had the 2.4.6 client and was able to make the jump with default tankspeed so this appears to only affect newer bz client versions.

The /handicap option or mode or setting appears to not be enabled on that server. Not sure if that could affect it or not but the server reports it is not being used if I type /handicap.

I've noticed this issue for roughly a yr now give or take and up till last week thought I was the only one experiencing the problem. I cannot recall what version I was running when first experienced it though.

Any help would be appreciated.

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Re: possible jumping related bug

Post by Bullet Catcher » Sat Jul 29, 2017 3:02 am

Frame rates affect jumping. Press the T key to display yours and tell us what it is for you on the map.

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Re: possible jumping related bug

Post by D-FENS » Thu Aug 03, 2017 12:49 pm

Roughly between 600 to 950 or so on the island map.

Noticed it drops to as low as 400 and as high as over 1000 on urban jungle.

Someone else had suggested limiting framerate but thought that would be considered cheating so never looked into it.

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Re: possible jumping related bug

Post by JeffM » Thu Aug 03, 2017 4:40 pm

frame rates that high can cause issues. You don't need over 120 fps. So yes, limit your frame rate to something reasonable. It's cheating when you limit it down to below like 30, because that lets you introduce fake lag.

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Re: possible jumping related bug

Post by D-FENS » Sat Aug 05, 2017 7:51 am

Tks all

set fps limit in options. Can not make the long jumps on the island map.

actual graphics quality is a bit lower but it's playable at least.

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Re: possible jumping related bug

Post by D-FENS » Sat Aug 05, 2017 6:33 pm

Thanks alot Jeff! This is how I recall bz responding years ago. Granted the graphics are not as smooth but the game feels like it did yrs ago and is much more responsive.

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Re: possible jumping related bug

Post by blast » Sat Aug 05, 2017 11:31 pm

I usually set the limit to around 100. You can use '/localset fpsLimit 100' for that.
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Re: possible jumping related bug

Post by Sky King » Fri Aug 18, 2017 3:37 am

JeffM wrote:
Thu Aug 03, 2017 4:40 pm
frame rates that high can cause issues. You don't need over 120 fps. So yes, limit your frame rate to something reasonable. It's cheating when you limit it down to below like 30, because that lets you introduce fake lag.
Hey, can someone help me understand from a technical standpoint how my GPU framerate could possibly affect the lag that others perceive or measure that I have? Are my client's positional reports to the server sync'ed to my GPU refresh cycles?
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Re: possible jumping related bug

Post by blast » Fri Aug 18, 2017 10:10 am

Because it's all part of the same game loop. Drawing, input handling, simulation, network code, and probably other stuff all take turns in the game loop. So lower FPS means that input, simulation, and network processing all get done fewer times per second.
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Re: possible jumping related bug

Post by JeffM » Fri Aug 18, 2017 5:39 pm

The frame rate is not just your GPU. The game tells the GPU to draw one frame every game loop cycle. So if the GPU takes too long, it makes the game loop wait till the drawing is done (the vast majority of time spend by the BZFlag process is waiting for drawing to happen). BZFlag is not a modern game, it does not let the GPU do things asynchronously. The entire game happens in one single thread.

So your frame rate is ALSO the rate that the game can process logic at. Part of that logic is sending and receiving network messages. So if the Frame rate is low, that's time that the system isn't spending sending data, aka time spent lagging.

Very low frame rates introduce lag. Very high frame rates make the simplistic math BZFlag uses for physics fail. The game loop compares how far everything has moved since the last loop (frame). At very high frame rates, these distances (deltas) are very small and start to run into floating point accuracy issues. For this reason high frame rates cause issues as well.

Optimally BZFlag would be rewritten with a more modern approach with separate Simulation (game logic and physics), Network, and Graphics threads, allowing each one to happen at it's own cycle rate.

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