| Microsoft DirectX 8.1 (C++) |
Hardware drivers can support special effects that do not fit into the categories defined by Microsoft® DirectInput®. The type-specific parameters for these effects may be either hard-coded or modifiable by the application.
If type-specific parameters are modifiable, the application developer must obtain a header file declaring the data structure required by the effect.
The hardware vendor must provide a GUID identifying the device-specific effect and might provide a custom structure for the type-specific parameters of the effect. Your application then must initialize a DIEFFECT structure and a type-specific structure, as with any other effect. You then call the IDirectInputDevice8::CreateEffect method, passing the device-specific GUID and a pointer to the DIEFFECT structure.
When you obtain information about a device-specific effect in a DIEFFECTINFO structure, the low byte of the dwEffType member (DIEFT_GETTYPE(dwEfftype)) indicates into which of the predefined DirectInput effect categories (constant force, ramp force, periodic, or condition) the effect falls. If it does not fall into any of the predefined categories, the value is DIEFT_HARDWARE.
If a device-specific effect falls into one of the predefined categories, the lpvTypeSpecificParams member of the DIEFFECT structure must point to the corresponding DICONSTANTFORCE, DIRAMPFORCE, DIPERIODIC, or DICONDITION structure, and the cbTypeSpecificParams member must be equal to the size of that structure.
If (DIEFT_GETTYPE(dwEfftype) == DIEFT_HARDWARE), the values of the lpvTypeSpecificParams and cbTypeSpecificParams members depend on whether the effect requires custom type-specific parameters. If it does, these values must refer to the appropriate structure defined in the manufacturer's header file and declared and initialized by your application. If the effect does not require custom parameters—that is, if the dwStaticParams member of the DIEFFECTINFO structure for the hardware effect does not have the DIEP_TYPESPECIFICPARAMS flag—lpvTypeSpecificParams must be NULL and cbTypeSpecificParams must be 0.
DirectInput passes the GUID and the DIEFFECT structure to the device driver for verification. If the GUID is unknown, the device returns DIERR_DEVICENOTREG. If the GUID is known but the type-specific data is incorrect for that effect, the device returns DIERR_INVALIDPARAM.