IVRIOBuffer
The IVRIOBuffer interface supports creating, reading from, and writing to a fixed-element-size cross-process, globally-named ring-buffer with extremely low synchronization overhead between multiple readers and a single writer. This interface is useful whenever there is very high-frequency of high-bandwidth data stream where it is acceptable for readers to fall behind and even miss elements in the stream, as this allows the writer to use a ring-buffer instead of an ever-growing buffer, and the writer can avoid writing if there are no readers.
An example of a high-frequency IVRIOBuffer stream is vr::ImuSample_t data arriving at 1000Hz from an HMD or at 250-500Hz from a tracked controller. In SteamVR, lighthouse-based HMDs and lighthouse-based tracked controllers expose a >= 512-element ring-buffer of IMU vr::ImuSample_t data under the name "/devices/lighthouse/<serial-number>/imu" with an element size of sizeof(vr::ImuSample_t). A driver or an application can read the IMU data as follows:
/* initialization */
vr::IOBufferHandle_t ulIMUStream;
vr::VR_Init(); // not necessary from an openvr driver
vr::VRIOBuffer()->Open( "/devices/lighthouse/LHR-D85D0087/imu", vr::IOBufferMode_Read, sizeof(vr::ImuSample_t), 0, &ulIMUStream );
/* whenever you want to process IMU data */
vr::ImuSample_t imuSamples[ 10 ];
uint32_t unRead;
while ( vr::VRIOBuffer()->Read( ulIMUStream, imuSamples, sizeof(imuSamples), &unRead ) == vr::IOBuffer_Success && unRead > 0 )
{
for ( uint32_t i = 0; i < unRead/sizeof(vr::ImuSample_t); i++ )
{
// process up to 10 samples at a time, you don't need to drain the available
// samples if you don't want to
}
}
/* when you’re done */
vr::VRIOBuffer()->Close( ulIMUStream );A driver or other application that wants to create its own IVRIOBuffer stream of data must specify the vr::IOBufferMode_Create | vr::IOBufferMode_Write flags to IVRIOBuffer::Open and provide the number of elements for the created ring-buffer:
/* initialization */
vr::IOBufferHandle_t ulMyStream;
vr::VRIOBuffer()->Open( "/my/custom/path", (vr::EIOBufferMode)(vr::IOBufferMode_Create|vr::IOBufferMode_Write), sizeof(MyDataStructure), 512, &ulMyStream );
/* write data whenever you like */
MyDataStructure myStruct;
vr::VRIOBuffer()->Write( ulMyStream, &myStruct, sizeof(MyDataStructure) );
/* when you're done */
vr::VRIOBuffer()->Close( ulMyStream );An example of an appropriate high-bandwidth IVRIOBuffer stream might be a stream of raw camera image data which requires 5MP per frame. A writer might create a 3-element fixed-size ring-buffer which multiple consumers could read from:
vr::IOBufferHandle_t ulCameraFrames;
vr::VRIOBuffer()->Open( "/path/to/my/camera/frames", (vr::EIOBufferMode)(vr::IOBufferMode_Create|vr::IOBufferMode_Write), 5*1024*1024*3, 3, &ulCameraFrames );