Microsoft DirectX 9.0

Device Properties

Properties of Microsoft?DirectInput?devices include the size of the data buffer, the range and granularity of values returned from an axis, whether axis data is relative or absolute, and the dead zone and saturation values for a joystick axis. Specialized devices can have other properties as well. For a list of properties defined by DirectInput, see IDirectInputDevice8::GetProperty.

With one exception—the gain property of a force-feedback device—properties can be changed only when the device is in an unacquired state.

Before calling the IDirectInputDevice8::SetProperty or the IDirectInputDevice8::GetProperty method you must set up a property structure that consists of a DIPROPHEADER structure and one or more elements for data. There is potentially a great variety of properties for input devices, and IDirectInputDevice8::SetProperty must be able to work with all sorts of structures defining those properties. The purpose of the DIPROPHEADER structure is to define the size of the property structure and how the data is to be interpreted.

DirectInput includes the following predefined property structures:

For IDirectInputDevice8::SetProperty, the data members of the property structure are the values that you want to set. For IDirectInputDevice8::GetProperty, the current value is returned in these members.

Before the call to IDirectInputDevice8::GetProperty or IDirectInputDevice8::SetProperty, the DIPROPHEADER structure must be initialized with the following:

When getting or setting properties for a whole device, the object identifier dwObj is 0, and the dwHow member is DIPH_DEVICE. If you want to get or set properties for a device object (for example, a particular axis), the combination of dwObj and dwHow values identifies the object. For details, see DIPROPHEADER.

After setting up the property structure, pass the address of its header into IDirectInputDevice8::GetProperty or IDirectInputDevice8::SetProperty, along with an identifier for the property that you want to obtain or change.

The following values are used to identify the property passed to IDirectInputDevice8::SetProperty and IDirectInputDevice8::GetProperty.

For more information about the last three properties, see also Interpreting Joystick Axis Data.

The following code example sets the buffer size for a device to hold up to 10 data items:

HRESULT      hr; 
dipdw.diph.dwSize = sizeof(DIPROPDWORD); 
dipdw.diph.dwHeaderSize = sizeof(DIPROPHEADER); 
dipdw.diph.dwObj = 0; 
dipdw.diph.dwHow = DIPH_DEVICE; 
dipdw.dwData = 10; 
hr = lpdiDevice->SetProperty(DIPROP_BUFFERSIZE, &dipdw.diph); 

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