| Microsoft DirectX 8.1 (C++) |
Before an effect can be played, it must be downloaded to the device. Downloading an effect means telling the driver to prepare the effect for playback. It is entirely up to the driver to determine how this is done. Generally, the driver places the parameters of the effect in hardware memory to minimize the subsequent transfer of data between the device and the system. The consequent reduction in latency is particularly important for conditions and for effects played in response to a trigger, such as a fire button. Ideally the device does not have to communicate with the system at all in order to respond to axis movements and button presses.
Downloading is done automatically when you create an effect, provided the device is not full and is acquired at the exclusive cooperative level. By default, it is also done when you start the effect or change its parameters.
If you specify the DIEP_NODOWNLOAD flag when changing parameters, you must subsequently use the IDirectInputEffect::Download method to download or update the effect.
When the device is unacquired—for example, when it has been acquired with the exclusive foreground cooperative level and the application moves to the background—effects are unloaded and must be downloaded again when the application regains the foreground. This is done automatically when you call the IDirectInputEffect::Start method, but you can choose to download all effects immediately on reacquiring the device. You always have to download effects associated with a trigger button, since the Start method is not normally called for such effects.
If your application gets the DIERR_DEVICEFULL error when downloading an effect, you must make room for the new effect by unloading an old one. You can remove an effect from the device by calling the IDirectInputEffect::Unload method. You can also remove all effects by resetting the device through a call to the IDirectInputDevice8::SendForceFeedbackCommand method.
When you create a force-feedback device, the hardware and driver are reset, so any existing effects are cleared.