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IDProjectCategoryView StatusDate SubmittedLast Update
0002295Zandronum[All Projects] Bugpublic2015-06-08 21:002018-05-09 09:51
Assigned ToLeonard 
PlatformOSOS Version
Product Version2.0 
Target Version3.1Fixed in Version3.1 
Summary0002295: Wall-jitter misprediction issue with high ping
Quote from Torr Samaho
Quote from unknownna
But I noticed a client-side misprediction that is not present in ZDaemon. You jitter when bumping into every wall in Zandronum.

It seems that the client is sometimes mispredicting how much the player is sliding against a wall, but only if the player changes his movement.
Steps To Reproduce1. zandronum -host
2. Connect a client to the server with an emulated ping of 603.
3. Join the game.
4. Move into walls at a slight angle with +forward and then release +forward.
Attached Files

- Relationships
related to 0000106feedbackLeonard Client mispredicts its z position in swimmable water online 
has duplicate 0002638closed Player prediction: desync when sliding on walls. 

-  Notes
User avatar (0018273)
Leonard (developer)
2017-09-11 17:32

Pull request.

With the test wad: simply typing "+forward;wait;-forward" in console with 200 ping is enough to get the desync every time.

The problem comes from the fact that the player prediction doesn't actually set the player's ticcmd but only passes it as an argument.
This is problematic because the physics code later use that ticcmd to determine velocity:
In p_mobj.cpp, line 2559:

    if (mo->velx > -STOPSPEED && mo->velx < STOPSPEED
        && mo->vely > -STOPSPEED && mo->vely < STOPSPEED
        && (!player || (player->mo != mo)
            || !(player->cmd.ucmd.forwardmove | player->cmd.ucmd.sidemove)))
User avatar (0018302)
Torr Samaho (administrator)
2017-09-17 16:10

Good finding! I just have a technical question, please see my comment on bitbucket.
User avatar (0019228)
StrikerMan780 (reporter)
2018-05-08 20:24

I used gamer proxy with a ping of 603, and tried bumping and sliding against the walls. I didn't seem to get any jitter/misprediction from doing so.

Issue Community Support
This issue is already marked as resolved.
If you feel that is not the case, please reopen it and explain why.
Supporters: unknownna Combinebobnt Daedalus
Opponents: No one explicitly opposes this issue yet.

- Issue History
Date Modified Username Field Change
2015-06-08 21:00 unknownna New Issue
2015-06-08 21:00 unknownna Status new => confirmed
2015-06-08 21:03 unknownna Summary Wall-jitter issue with high ping => Wall-jitter misprediction issue with high ping
2017-09-11 17:06 Dusk Relationship added has duplicate 0002638
2017-09-11 17:06 Dusk Relationship added related to 0000106
2017-09-11 17:07 Dusk Status confirmed => needs review
2017-09-11 17:32 Leonard Note Added: 0018273
2017-09-11 18:48 Dusk Target Version => 3.1
2017-09-17 16:10 Torr Samaho Note Added: 0018302
2017-09-17 16:10 Torr Samaho Status needs review => feedback
2017-10-04 16:16 Leonard Status feedback => needs testing
2017-10-23 15:05 Leonard Status needs testing => assigned
2017-10-23 15:05 Leonard Assigned To => Leonard
2017-10-23 15:06 Leonard Status assigned => needs testing
2018-05-08 20:24 StrikerMan780 Note Added: 0019228
2018-05-09 09:51 Leonard Status needs testing => resolved
2018-05-09 09:51 Leonard Resolution open => fixed
2018-05-09 09:51 Leonard Fixed in Version => 3.1

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