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those signatures don't look compatible

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what are you doing?

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how does hook_callback looks like?

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my guess is that you don't need &mut self

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that seems to be the difference between your function and what the callback expects

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https://learn.microsoft.com/en-us/windows/win32/api/winuser/nc-winuser-hookproc

HOOKPROC (winuser.h) - Win32 apps

An application-defined or library-defined callback function used with the SetWindowsHookEx function. The system calls this function after the SendMessage function is called. The hook procedure can examine the message; it cannot modify it.

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is this the function?

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you have to match that function signature exactly

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that is what the system expects

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adding or removing arguments is not something you're allowed to do

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I'm not on windows to check it out well

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my guess is that if you want to keep state between calls, you need a static/thread local variable

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I don't see any other way you could make this work

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why can't you define a static var?

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you can have a struct with some data that is static that you access from all the functions

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struct MyStuff {
    x: i32,
    y: i32,
}

static mut CTX: MyStuff = MyStuff { x: 0, y: 0 };

fn main() {
    unsafe { CTX.x = 5; }
}

disclaimer: ^ not 100% safe if multiple threads are involved

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it's not pretty, but windows doesn't give you another option in this case

#help