Creating a DirectInput Device

To get input data from a device, you first have to create an object to represent that device.

The IDirectInput8::CreateDevice method is used to obtain a pointer to the IDirectInputDevice8 interface. Methods of this interface are then used to manipulate the device and obtain data.

The following code example, where lpdi is a pointer to the IDirectInput8 interface, creates a keyboard device:

LPDIRECTINPUTDEVICE8  lpdiKeyboard; 

lpdi->CreateDevice(GUID_SysKeyboard, &lpdiKeyboard, NULL); 

The first parameter in IDirectInput8::CreateDevice is an instance globally unique identifier (GUID) that identifies the instance of the device for which the interface is to be created. Microsoft?DirectInput?has two predefined GUIDs, GUID_SysMouse and GUID_SysKeyboard, which represent the system mouse and keyboard. You can pass one of these identifiers into the IDirectInput8::CreateDevice method. The global variable GUID_Joystick should not be used as a parameter for IDirectInput8::CreateDevice because it is a product GUID, not an instance GUID.

DirectInput provides four other predefined GUIDs primarily for testing.

•     GUID_SysKeyboardEm

•     GUID_SysKeyboardEm2

•     GUID_SysMouseEm

•     GUID_SysMouseEm2.

Passing one of these GUIDs to IDirectInput8::CreateDevice grants access to the system keyboard or mouse through an emulation layer, at either level 1 or level 2. These GUIDs always represent the system mouse or keyboard. They are aliases for GUID_SysKeyboard and GUID_SysMouse, so they are not enumerated by IDirectInput8::EnumDevices or IDirectInput8::EnumDevicesBySemantics unless the DIEDFL_INCLUDEALIASES flag is passed.

For devices other than the system mouse or keyboard, use the instance GUID for the device returned by IDirectInput8::EnumDevices or IDirectInput8::EnumDevicesBySemantics. The instance GUID for a device is always the same. You can allow the user to select a device from a list of those enumerated, then save the GUID to a configuration file and use it again in later sessions.