Trouble understanding OpenVR driver API

Question

My end goal is to make a VRidge lightweight clone to understand the OpenVR API, but I'm struggling to understand how to get my code to display something. As a starting point, instead of my phone, I want to create a window as the HMD (SFML, SDL, you name it...) and having SteamVR rendering the VR view in it.

I understand that an object implementing IServerTrackedDeviceProvider is the handler of my driver's devices, ITrackedDeviceServerDriver is the interface of the device itself, and I suspect that my "HMD" device will have to implement IVRDisplayComponent.

Aside from setting some properties and having callbacks to activate and deactivate my device, I have no clue where to get an actual frame to display on the screen. What am I missing ?

Answer 1

You are almost right.

A class inheriting vr::IServerTrackedDeviceProvider(I'll call it the device parent later on) is responsible for registering and maintaining the lifetime of your devices(creating them, registering them, etc.)

Classes inheriting vr::ITrackedDeviceServerDriver after they have been registered by a device parent are considered a tracked device, device type is set by the device parent on register, also in case of the HMD device GetComponent() method needs to return display components if requested, for other devices it can just return NULL

GetComponent() receives a c string with a component name and version, for example "IVRDisplayComponent_002" stored in vr::IVRDisplayComponent_Version, and if the device has a component with a matching name version pair you need to return a pointer to it, if no match is found return NULL

Also about components, in the driver example that Valve provides its done in a very lazy and bad way, DO NOT INHERIT COMPONENTS TO YOUR DEVICE CLASSES

Segment your components into separate objects that you initialize in your device and return them in GetComponent() accordingly

Now, the only thing left for your devices to be properly identified and used by SteamVR is registering them, but there is a catch, you need to specify the device type when you register it by passing one of the values from vr::ETrackedDeviceClass enum(these should be pretty self explanatory when you look at the enum)

This is not all there is to openvr driver of course, for it all to work and for SteamVR to even acknowledge your driver's existence you need to implement an HmdDriverFactory() function, its similarly to GetComponent() except you compare the input c string to a provider name version pair and in case of a device parent its vr::IServerTrackedDeviceProvider_Version, if you get a match return a pointer to the instance of your device parent or any other provider you implemented

A few notes:

• HMD needs at least one display component
• HMD device is very sensitive to how you submit poses to it(dont ask why, it just is)
• Be prepared for the lack of documentation, the best docs that you're gonna get are code comments in openvr_driver.h, ValveSoftware/openvr issue tracker and other people working with openvr drivers (even though there are only few...)

This is not the best explanation of how openvr drivers work, so you're always welcomed to ask for more details in the comments