When issuing ALT + Tab in on client, tab gets stuck indefinitely unless interrupted with ALT or Tab key again

[ghnand]

I have tested this with several hosts (windows 10) and clients (Windows 10, Mac OSX, Linux), as well as different physical keyboards, however the issue persists across all variations.

How reproducible: enable scroll lock. Launch ultravnc viewer and connect to client Press ALT + Tab and release both. As you would when switching between windows normally.

The client behaves as if tab is held down and cycles through the window.

[Neustradamus]

@RudiDeVos: Can you look?

[charlescanato]

I've found this same problem - in my case this is the client running on Win7 and connecting to Kubuntu 22.04 running krfb.

Still, the same problem, only that it begins to happen right when you release the TAB key. Of course, when you release the ALT key, nothing changes and the current window keeps "tabbing".

[wharlox]

This has got to be the most frustrating problem I can think of; client is x11vnc and win10 using uvnc from 1.3.x through 1.4.09 (probably even older versions; I'll have to check now).

I can guarntee this is an ultravnc problem as tightvnc was unable to replicate the issue. It is not a keyboard-driver issue either as I am able to reproduce it using the On Screen Keyboard with windows:

• click alt so it holds it in active position
• tap on Tab a few times
• watch Tab be spammed a million times uncontrolably like if Tab is being held down

Will edit/post if i see results with older versions of this.

[wharlox]

Seems this is part of the implementation, to not send a tab-up signal - hopefully some easy logic can be added to prevent the tab from sending indefinitly

https://github.com/ultravnc/UltraVNC/blob/ee9954b90ab6b52a2332b349d55f6a98af3f7424/vncviewer/LowLevelHook.cpp#L318-L339

[RudiDeVos]

We end key down and key up seperate. If mouse is over viewer with down and the up is pressed outsite the viewer the key stay down on the remote PC. Some auto reset could do the trick..if it doesn't break other cases, on the list to verify.

Was this with scrollock on ?

[wharlox]

• uvnc is in windowed or full-screen mode; mouse exclusively within the vnc window
  • scrolllock is disabled; alt-tab occurs exclusively on the host (in this case, windows)
  • scrolllock enabled; alt-tab occurs exclusively on the remote host; tab can get immediately stuck and does not release until spamming tab a few times. releasing alt and alt-tab stops, but tab still spams; holding tab resumes alt-tab inside host

maybe an added option to test out a new flow for the alt-tab; i'd be willing to test that

[Neustradamus]

@RudiDeVos: Have you seen the latest @wharlox comment?