HTC Drivers {#htc-drivers} #

[TOC]

This file is meant to explain the design complexities of our "HTC Config" headset handling code (aux/htc, d/vp2). It assumes a level of familiarity with how Lighthouse HMDs function.

aux/vive #

Beginning with the original HTC Vive, this implements shareable routines for Lighthouse HMDs, extending to headsets such as the Valve Index, Bigscreen Beyond, HTC Vive Pro 1, etc.

At it's core is the Lighthouse JSON Config (known officially as The JSON File), parsed by vive_config.c. This contains most of the information describing how the headset operates, including display and IMU calibration, photodiode positions for tracking, and much more.

aux/htc #

Some more modern HTC headsets which have Lighthouse support (Vive Pro 2, Vive Cosmos + Vive Cosmos External Tracking Faceplate) have a second JSON configuration file containing data separate from the Lighthouse config, colloquially known as the "HTC Config". aux/htc implements shareable routines relating to this configuration file.

This originates from headsets like the Vive Cosmos which by default do not have any Lighthouse support, and so do not contain a Lighthouse configuration file, necessitating something custom. However, even in later Lighthouse headsets, like the Vive Pro 2, this side-channel configuration file is still present and contains vital information for making the headset functional.

At the core of aux/htc's utility is an implementation of HTC's many custom display distortion algorithms, most of which are much more complex than the one used on standard lighthouse devices.

d/vp2 #

This driver implements the Vive Pro 2 specific protocol, which is used to set brightness, read the HTC Config, change microphone noise cancelling, display mode, and more. The HTC config present in the Vive Pro 2 also contains extra information not present in other HTC configs, so d/vp2 has a structure which extends the HTC Config with data only present on Vive Pro 2. It uses aux/htc to parse out the shared data.

Importantly, it does not contain any code relevant to tracking, and does not implement the xrt_device interface, this driver is intended to be initialized by other drivers, to provide Vive Pro 2 specific functionality that isn't covered by the Lighthouse protocol.

d/vive #

This is a driver which directly interfaces with true Lighthouse headsets to drive the headset and implement the xrt_device interface. It uses aux/vive to parse the Lighthouse configuration.

As of now, it does not have integrations for Vive Pro 2 or other HTC Config headsets.

d/survive #

This driver uses the libsurvive library to implement the xrt_device interface. When a Vive Pro 2 is detected, this driver imports d/vp2 and aux/htc to provide any functionality required, such as replacing the display distortion algorithm with the one provided by aux/htc.

d/steamvr_lh #

d/steamvr_lh implements a runner for the OpenVR driver interface, using it to implement the xrt_device interface, acting as a bridge between OpenVR drivers and Monado.

Similar to d/survive, when a Vive Pro 2 is detected, any functionality not available through normal means is implemented using d/vp2 and aux/htc.