Buffered and Immediate Data
DirectInput supplies two types of data: buffered and immediate. Buffered data is a record of events that are stored until an application retrieves them. Immediate data is a snapshot of the current state of a device.
You might use immediate data in an application that is concerned only with the current state of a device - for example, a flight combat simulation that responds to the current position of the joystick and the state of one or more buttons. Buffered data might be the better choice where events are more important than states - for example, in an application that responds to movement of the mouse and button clicks. You can also use both types of data, as you might, for example, if you wanted to get immediate data for joystick axes but buffered data for the buttons.
For devices that do not generate interrupts, such as analog joysticks, DirectInput does not obtain any data until you call the IDirectInputDevice8::Poll method. For more information, see Polling and Event Notification.
For examples of retrieving buffered data, see IDirectInputDevice8::GetDeviceData.