How can I deal with depressed Windows logo key when using `SendInput`?

Question

My application synthesises keystrokes in other apps by using SendInput. This almost works, except that due to circumstances I cannot change, the left Windows key will always be physically depressed when sending the input. This means that if, for example, the keystroke being sent is the 'd' key, then Windows sees the keystroke as its Win+D shortcut and displays the Desktop, and the 'd' keystroke never makes it to its intended target.

The documentation mentions this problem but is frustratingly vague about how to fix it (emphasis mine):

This function does not reset the keyboard's current state. Any keys that are already pressed when the function is called might interfere with the events that this function generates. To avoid this problem, check the keyboard's state with the GetAsyncKeyState function and correct as necessary.

How should I "correct as necessary"?

I've tried using SetKeyboardState to turn off the keyboard state of the VK_LWIN key, after first attaching my thread to the thread of the window that I am sending the keystrokes to (with AttachThreadInput), but this doesn't seem to affect the behaviour at all.

I've also tried inserting a KEYEVENTF_KEYUP event at the start of the input I am sending with SendInput, but this causes the Start Menu to pop up and grab focus, which is obviously not acceptable.

What is the correct method of dealing with a depressed Windows logo key when calling SendInput?

EDIT:

As per @Brian's answer I can prevent the win key from interfering with my code by installing a low-level keyhook which traps win-key keydown events.

This, however, has the undesired effect that the Windows key is now disabled entirely. I can sort of envisage some solution to this where I keep a note of the state of all the keys within my keyhook, and simulate presses of the windows key when other keys are pressed, depending on whether or not they are the ones I'm simulating, but that sounds like a hack to me. Alternatively, I could use my keyhook to emulate important windows keyboard shortcuts.

But the documentation implies it should all work in a much more straightforward way. Brian's solution is to prevent the win key from getting to the pressed down state in the first place. But the documentation states that you should be able to check if it's pressed down later on, and correct it if it is.

Is it actually possible to do this?

Answer 1

I basically solved this exact problem yesterday :) My code is in C#, but it mostly consists of win32 API calls via p/invoke, so it should translate directly to C++.

The solution is to use a Low-Level Keyboard Hook to intercept the initial Windows key KeyDown event (and tell the OS that you handled it so that it won't be passed to other Applications and/or the OS). Then, depending on OS, simulate the Windows key KeyUp event before your input. It sounds like you're half-way there, you just need to intercept the initial KeyDown.

My solution is targeted at Windows Vista and Windows 7, so if you're in XP or below, it's possible that you don't need to send the KeyUp. That's what I'll be testing soon, it may work in both; however, Vista and 7 intercept the windows key more aggressively than XP, hence my suspicions.

Answer 2

There is not a more "straightforward way" for a program to do this without modifying the registry. The ideal solution is to track the keypresses in a table (std::map, Dictionary, etc). The intent of this on MS's part is to prevent viruses/malware from taking control of the keyboard and preventing the user from using important keyboard combos such as WinKey-L and Ctrl-Alt-Delete.

You can, however, remap the keyboard scan codes in the registry if keyboard hooking is not for you. This isn't ideal, since it's hard to reverse (especially if you make a mistake, or your program crashes, or the user uninstalls the application but the registry hack is not reverted). But it does work. Here are some references:

http://www.howtogeek.com/howto/windows-vista/map-any-key-to-any-key-on-windows-xp-vista/

http://www.howtogeek.com/howto/windows-vista/disable-caps-lock-key-in-windows-vista/

http://www.usnetizen.com/fix_capslock.php

Answer 3

"Correcting" the state of a modifier key by inserting a KEYEVENTF_KEYUP event may have side-effects, but they can be avoided by inserting additional events.

The Start menu is triggered when the Win key is pressed and released, except when there is an intervening key event or if it was pressed in combination with another modifier. So instead of inserting just Win-up, insert Ctrl-down, Win-up, Ctrl-up.

Aside from the Start menu, releasing modifier keys might have other side-effects:

• Releasing Alt can activate the active window's menu (even if it doesn't appear to have one).
• Releasing Alt or Shift can activate the Alt+Shift language hotkey.
• Releasing Ctrl or Shift can activate the Ctrl+Shift language hotkey.
• Releasing any modifier key can activate the Office hotkey (in Windows 1903 and later, pressing and releasing Ctrl+Alt+Shift+Win opens the Office app).

Inserting a key-down and key-up (or possibly just a key-up without a prior key-down) with almost any other virtual keycode first will generally prevent any of these hotkeys from activating. One can use an undefined or reserved keycode such as 0xE8, although there is still a risk that another program makes use of it.