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Understanding DirectInput

This topic covers the underlying structure of Microsoft DirectInput and its relationship to the Microsoft Windows message system.

For practical information about how to implement the elements of DirectInput introduced here, see Using DirectInput.

DirectInput Objects

An input-only DirectInput implementation consists of the DirectInput object, which supports IDirectInput8 Interface, a Component Object Model (COM) interface, and a DirectInputDevice object for each input device that provides data. Each DirectInputDevice object in turn has device objects, which are individual controls or switches, such as keys, buttons, or axes. Device objects are also called device object instances.

Each DirectInputDevice object represents one input device, such as a mouse, keyboard, or joystick. In the DirectInput API, the word joystick means any type of input device other than a mouse or keyboard. A piece of hardware that is really a combination of different types of input devices, such as a keyboard with a touchpad, can be represented by two or more DirectInputDevice objects. A force-feedback device is represented by a single joystick object that handles both input and output.

DirectInputDevice objects instantiate the IDirectInputDevice8 Interface. The application ascertains the number and type of device objects available by using the IDirectInputDevice8::EnumObjects method. Individual device objects are not encapsulated as code objects, but are described in DIDEVICEOBJECTINSTANCE structures.

All DirectInput interfaces are available in ANSI and Unicode versions. If "UNICODE" is defined during compilation, the Unicode versions are used.

Interaction with Windows

Because DirectInput works directly with the device drivers, it either suppresses or ignores Windows mouse and keyboard messages. It also ignores mouse and keyboard settings made by the user in Control Panel. It does, however, use the calibrations set for a joystick or other game controller.

DirectInput does not recognize keyboard character repeat settings. When using buffered data, DirectInput interprets each press and release as a single event with no repetition. When using immediate data, DirectInput is concerned only with the present physical state of the keys, not with keyboard events as interpreted by Windows.

DirectInput does not perform any character conversion or translation. For example, the SHIFT key is treated like any other key, not as a modifier of another keypress. Keys return the same identifiers regardless of the user's system language settings.

Under Windows 2000, acquiring the keyboard in exclusive mode prevents any applications that are subsequently launched from receiving keyboard data.

Because DirectInput works directly with the mouse driver, it bypasses the subsystem of Windows that interprets mouse data for windowed applications. Applications that rely on the Windows cursor for navigation should continue to use the standard Windows mouse messages and Microsoft Win32 functions.

When using the system mouse in exclusive mode, DirectInput suppresses mouse messages, and therefore Windows is unable to show the standard cursor.

DirectInput ignores Control Panel settings such as acceleration and swapped buttons. However, DirectInput recognizes settings in the driver itself. For example, if the user has a three-button mouse and uses the driver-utility software to make the middle button a double-click shortcut, DirectInput reports a click of the middle button as two clicks of the primary button.

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