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Asked: 2026-06-13T23:03:32+00:00

I’ve done some research (with single input device altrough) in this field and discovered

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I’ve done some research (with single input device altrough) in this field and discovered that in most situations messages are sent by pair, first WM_INPUT and then WM_KEYDOWN. So it’s merely possible to link them together for filtering, i.e. WM_INPUT flags that it’s corresponding WM_KEYDOWN shoudn’t be sent to reciever (in my case first i discard all WM_KEYDOWN and then decide whenever i need to send them back to their recipients). I just assume that all next WM_KEYDOWN are belong to last WM_INPUT.

My question exactly: can i seriously rely on that principle? Won’t those messages mix up if i use multiple input devices?

There are some serious questions about its reliability already:
1. How do i distinguish repeating input from multiple devices (answer is obvious – i can’t).
2. Would WM_INPUT-WM_KEYDOWN pairs mix up in case of input from multiple devices? i.e. form an cortege like WM_INPUT, WM_INPUT, WM_KEYDOWN, WM_KEYDOWN?

Also maybe it is possible to just discard all WM_KEYDOWN and generate all keyboard events by myself? Altrough it would be technically quite difficult, because there may be multiple WM_KEYDOWNs from one WM_INPUT (key repeatence work that way, multiple WM_KEYDOWN, one WM_KEYUP).

Just in case, here’s what i need to achieve:
I need to filter all messages by time between them. All user input gets filtered by time interval between keypresses. If two messages were sent with interval <50ms i discard first message and second awaits while its TTL exceeds and if so, it sent to its recipient.
Difficulty is that there can be multiple input devices and those timings will mess up with each other.

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1 Answer

  1. Editorial Team

    I figured out that keyboard hook (WH_KEYBOARD) actually occurs before WM_KEYDOWN message, can’t check if simultanious input from several devices will mess up order of WM_INPUTS and KeyboardHook events (like sequence of events: Dev0_WM_INPUT Dev1_WM_INPUT Dev0_KBDHook Dev1_KBDHook – altrough that sequence of event will be handle, what i fear is if Dev1_KBDhook will appear before Dev0_KBDhook or worse).

    With WM_KEYDOWN such mess was possible, still don’t know if it will be same with keyboad hook.

    Anyway it is possible solution. On WM_INPUT i create Message itself and partly fill, on next KeyboardHookEvent i just fill remaining part.

    Generally WM_INPUTs and KeyboardHook events occur by pairs, but as i mentioned before, i don’t exactly know if it can mess up, but if even so, if it will maintain order of KeyboardHookEvents and WM_INPUTS (like Dev0_INPUT, Dev1_INPUT and then Dev0_KBDEvent, Dev1_KBDEvent) it will give no trouble to parse those sequences. For example one stack:
    WM_INPUT pushes new message struct, KBDEvent pops and fill remaining parts.

    Not generally good solution, but i guess it is good enough to use if no other exists, solves the problem, atleas partially.

    If i’ll manage to test its behavious upon simultanious input from multiple devices, i will post info here. Altrough i really doubt there will be any mess that can’t handled. Unless windows chooses time to send corresponding keyboard event by random…

    Forgot to mention, yes it’s partially possible to discard all input and generate manually. I just PostMessage manually forged message (i get lparam from KeyboardHookEvent). But it will give some problems. Like hotkeys won’t work and also anything that uses GetAsyncKeyState. In my case it is acceptable altrough.

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