Periodic Effects

Periodic effects are waveform effects. DirectInput defines the following forms:

·Square

·Sine

·Cosine

·Triangle

·SawtoothUp The waveform drops vertically after it reaches maximum positive force. See the example at Basic Concepts of Force Feedback.

·SawtoothDown The waveform rises vertically after it reaches maximum negative force.

An envelope can be applied to periodic effects. See the example at Basic Concepts of Force Feedback.

The phase of a periodic effect is the point along the waveform where the effect begins. Phase is measured in hundredths of a degree, from 0 to 35,999. The following table indicates where selected phase values (in degrees) lie along the various waveforms. Max is the top (+) or bottom (-) of the wave and Mid is the midpoint, where no force is applied in either direction.

A driver may round off a phase value to the nearest supported value. For example, for a sine effect some drivers support only values of 0 and 9,000 (to create a cosine); for other effects, only values of 0 and 18,000 are supported.

To create a periodic force, pass one of the following values in the rguid parameter of the IDirectInputDevice2::CreateEffect method:

·GUID_Square

·GUID_Sine

·GUID_Triangle

·GUID_SawtoothUp

·GUID_SawtoothDown

You can also pass any other GUID obtained by the IDirectInputDevice2::EnumEffects method, provided the low byte of the dwEffType member of the DIEFFECTINFO structure (DIEFT_GETTYPE(dwEfftype)) is equal to DIEFT_PERIODIC. In this way you can use hardware-specific forces designed by the manufacturer. For example, a hardware device might support a periodic effect that rotates the stick in a small circle.

The type-specific structure for periodic effects is DIPERIODIC. For more information on the dwPhase member of this structure, see the overview of Periodic Effects.