LockCursorToPrimaryMonitor.ahk

/*
	; Holding down left Control key to lock, release to unlock.
	~LControl::
		LockCursorToPrimaryMonitor(true)
		KeyWait, LControl
		LockCursorToPrimaryMonitor(false)
	return
*/

LockCursorToPrimaryMonitor(lock = true) {
	; Get mouse position on screen
	VarSetCapacity( pt, 8, 0 )
	DllCall("GetCursorPos", "Ptr", &pt)
	x := NumGet(pt, 0, "Int")
	
	; If the cursor already on the second monitor, then leave it there.
	if (x > A_ScreenWidth) {
		return
	}

	; ClipCursor -- https://msdn.microsoft.com/en-us/library/windows/desktop/ms648383(v=vs.85).aspx
	if (lock) {
		VarSetCapacity(rect, 16, 0)
		NumPut(A_ScreenWidth, rect, 8)
		NumPut(A_ScreenHeight, rect, 12)
		DllCall("ClipCursor", "ptr", &rect)
	} else {
		DllCall("ClipCursor", "ptr", 0)
	}
}