![]() This means that calling the SendInput function while input is blocked will change the asynchronous keyboard input-state table. Note, the BlockInput function will not interfere with the asynchronous keyboard input-state table. To block keyboard and mouse input events from reaching applications, use BlockInput. When the default window procedure receives the WM_ACTIVATE message, it sets the keyboard focus to the active window. The low-order word of the wParam parameter is zero if the window is being deactivated and nonzero if it is being activated. When one window is deactivated and another activated, the system sends the WM_ACTIVATE message. It can determine whether a top-level window it created is active by using the GetActiveWindow function. A thread can activate a top-level window by using the SetActiveWindow function. The user can activate a top-level window by clicking it, selecting it using the ALT+TAB or ALT+ESC key combination, or selecting it from the Task List. ![]() To help the user identify the active window, the system places it at the top of the Z order and highlights its title bar (if it has one) and border. The window with the keyboard focus is either the active window, or a child window of the active window. The active window is the top-level window the user is currently working with. The concept of keyboard focus is related to that of the active window. When the keyboard focus changes from one window to another, the system sends a WM_KILLFOCUS message to the window that has lost the focus, and then sends a WM_SETFOCUS message to the window that has gained the focus. A thread can give the keyboard focus to one of its windows by calling the SetFocus function. The window that has the keyboard focus receives (from the message queue of the thread that created it) all keyboard messages until the focus changes to a different window.Ī thread can call the GetFocus function to determine which of its windows (if any) currently has the keyboard focus. The system shares the keyboard among all windows on the display by shifting the keyboard focus, at the user's direction, from one window to another. The keyboard focus is a temporary property of a window. ![]() The system posts keyboard messages to the message queue of the foreground thread that created the window with the keyboard focus. The following figure illustrates the keyboard input model. Eventually, the thread's message loop removes the message and passes it to the appropriate window procedure for processing. The system removes the message from the system message queue and posts it to the message queue of the appropriate thread. After translating a scan code, the keyboard layout creates a message that includes the scan code, the virtual-key code, and other information about the keystroke, and then places the message in the system message queue. The keyboard device driver interprets a scan code and translates (maps) it to a virtual-key code, a device-independent value defined by the system that identifies the purpose of a key. A keyboard generates two scan codes when the user types a key-one when the user presses the key and another when the user releases the key. The keyboard device driver receives scan codes from the keyboard, which are sent to the keyboard layout where they are translated into messages and posted to the appropriate windows in your application.Īssigned to each key on a keyboard is a unique value called a scan code, a device-dependent identifier for the key on the keyboard. The system provides language-independent keyboard support by using the language-specific keyboard layout currently selected by the user or the application. The system provides device-independent keyboard support for applications by installing a keyboard device driver appropriate for the current keyboard. An application receives keyboard input in the form of messages posted to its windows. Applications should accept user input from the keyboard as well as from the mouse.
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