Josip Almasi, 10/17/2021 04:47 PM
h2. External resources
Demo site: https://www.vrspace.org/
Github project page: https://github.com/jalmasi/vrspace
OpenSource.com article (motivation): https://opensource.com/article/20/12/virtual-reality-server
VR Days video (features, technologies): https://vimeo.com/475142708
Youtube channel: https://www.youtube.com/channel/UCLdSg22i9MZ3u7ityj_PBxw
Facebook page: https://fb.com/vrspace.org
Client API jsdoc: https://www.vrspace.org/docs/jsdoc/index.html
Server javadoc: https://www.vrspace.org/docs/javadoc/index.html?overview-summary.html
Multi-user interaction, shared objects: https://playground.babylonjs.com/#ZBK155
Multi-user world: https://playground.babylonjs.com/#Y6ILJ5
Avatar selection, portals: https://playground.babylonjs.com/#HDV7LA
VR Avatar template world: https://www.babylonjs-playground.com/#VXA0R3
h1. Frequently Asked Questions
h2. Is this open source, free to use and share?
Yes, it's all free and open. Server and client code is published under Apache 2 license, all 3D models published by their respective authors under Creative Commons Attribution license.
h2. Is there any documentation?
This is good place to start, this page links to all available resources.
h2. How many users can share a “world/space” simultaneously?
By default, number of users per space is not limited. There is a server parameter to limit that (org.vrspace.server.maxSessions) that can be specified either in config file or command line. Users that hit the limit remain in the queue for configurable timeout (org.vrspace.server.sessionStartTimeout, zero by default) until someone leaves. An error is raised on timeout.
h2. How can I implement custom authentication and/or authorization?
Typically you will authenticate users on your web server, before they enter the world.
If that's not enough, you can implement your own "ClientFactory":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/core/ClientFactory.java and configure it in "application.properties":https://github.com/jalmasi/vrspace/blob/master/server/src/main/resources/application.properties file.
This allows you to do your own database queries, REST calls or whatever else you may need to identify your users.
h2. How is that different from a game server?
It's not all that different, though the emphasis is different: vrspace.org is not focused on games specifically. It's more about multi-user 3D web, in particular WebXR, open standards and open source.
So while game servers usually don't bother with video/audio streaming, vrspace.org provides it out of the box, using WebRTC. On the other hand, there's nothing like game level in vrspace.org.
h2. How does inverse kinematics and motion tracking work in vrspace.org characters?
Everything is encapsulated Avatar class, but relies on observed glTF avatar structure. Heuristics used to analyze the character structure is explained in depth in "this paper":https://redmine.vrspace.org/attachments/download/17/vrspace-characters.doc.
h1. Setting up development environment
Here's all you need to start development on Windows.
Linux distributions include all these tools as native packages, so no additional downloads should be required.
h2. Basic setup
h3. Git bash
IDEs can work with github directly, but whatever you ask, you'll get a command line answer.
Command line git is simply a must have. Bash also includes a lot of goodies like ssh.
Java 8 will work, java 11 recommended. JDK is required to build the server.
Get it either from Oracle or elsewhere, e.g. Zulu OpenJDK: https://www.azul.com/downloads/zulu-community/?package=jdk
Mind that IDE will complain if you installed unsupported version of Node; should that happen, remove Node, and install latest one supported.
Get it from https://nodejs.org/
Apache Maven is used to build the server from command prompt.
Get it from https://maven.apache.org/download.cgi
Eclipse for Java developers (not enterprise), with Spring and Web plugins:
Download eclipse here: https://www.eclipse.org/
And then go to Help -> Eclipse Marketplace
Search and install Spring Tools 4 and Wild Web Developer plugins.
You'll also need to download and install https://projectlombok.org/
Once done, restart the eclipse.
h2. Import and start the project
In Eclipse, you can use either default or new workspace for the project.
Assuming you have cloned the project from the github,
Go to File -> Open Projects From the Filesystem
Then choose vrspace directory.
This will import vrspace folders and project subfolders, click Finish.
In vrspace project folder, in src/main/java, there's org.vrspace.server.ServerApplication.java.
Open it, then right click on the code.
From the menu, choose either Run as or Debug as -> Spring Boot App.
Open http://localhost:8080/babylon/connect.html with two browsers, and navigate around.
That's all, you're all set!
h3. git bash
git clone https://github.com/jalmasi/vrspace.git
mvn clean install
java -jar server/target/server-0.2.2.jar
h2. Advanced setup
HTTPS is required for pretty much everything - WebXR, camera, mic access.
By default, the server runs on 8080 port with plain HTTP. To enable HTTPS, edit application.properties (found in src/main/resources), and change following properties:
# default port 8080
Apache reverse proxy setup, linux, windows, TBD
h3. Docker and OpenVidu
OpenVidu voice/video chat server runs as docker image. This is only required for development of voice chat functions.
Local execution (development):
docker run -p 4443:4443 --rm -e OPENVIDU_SECRET=YOUR_SECRET -e DOMAIN_OR_PUBLIC_IP=YOUR_IP openvidu/openvidu-server-kms:2.17.0
Running on server:
Then either modify openvidu.publicurl and openvidu.secret in application.properties, or run server.jar with -Dopenvidu.publicurl=YOUR_URL and -Dopenvidu.secret=YOUR_SECRET
h1. Software Architecture
h2. Client-Server Communication
General approach to communication is rather obscure Half-Object pattern: server-side and client-side object have same properties, but different implementations.
Whenever an object's property changes in (any) client's address space, it's transmitted to the server, that broadcasts it to all clients currently 'watching' the object.
Whenever a client wants to perform any change to any object in the space, it has to go through the VRSpace server.
Clients may or may not communicate directly, but this is out of the scope of VRSpace server.
h2. Server Responsibilities
Sole responsibility of VRSpace server is management of 3D space: persisting space objects, tracking their properties, processing and distributing events from/to objects.
Whenever we talk about objects, that includes clients, i.e. users - a client is a special case of an object.
The server does not even handle the authentication - it is assumed to be responsibility of web app serving the space.
3D geometry is also not in server's scope, it's just another property of an object (mesh).
h2. Server design
Key concepts here are Active Objects, Actor model, and Live distributed object.
"VRObject":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/obj/VRObject.java is a basic shared object, with some basic properties like position and rotation, and of course, mesh. It essentially a "Live distributed object":https://en.wikipedia.org/wiki/Live_distributed_object.
"Client":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/obj/Client.java extends VRObject, and adds capabilities to communicate over web sockets, and listen to changes to other objects. Typically, a client represents a remote user, but it can also represent a robot connected over a web socket, or be a base class for a server-side robot.
A Client can be thought of as "Active Object":https://en.wikipedia.org/wiki/Active_object or an "Actor":https://en.wikipedia.org/wiki/Actor_model,
Server relies on Spring Boot and embedded Tomcat to handle all I/O and threads.
Each "Client":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/obj/Client.java has it's own "Scene":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/core/Scene.java that tracks all shared objects - including other clients - visible by the client. The scene is initially populated once the client logs in to the server, and starts the session. Scene is refreshed periodically, after a movement, or explicitly.
Scene maintains the event model, by adding the Client as listener to all other active objects (usually other users) in the scene.
Client simply notifies it's own listeners on any changes to any of it's own properties. As a listener, it propagates any observed change on any other object over the network, to the user.
Client has just a couple of persistent properties, like position, rotation and name. The name must be unique.
All other properties are transient.
"ClientFactory":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/core/ClientFactory.java allows for customization of Client class and instances.
h3. Events and messages
Typically events exchanged are changes to properties of active objects, e.g. user moves around, changing own position and rotation. However, an object may emit any event, and the event gets propagated to all listeners.
This is to simplify client development: simply emit any custom event you want.
All distributed events are encapsulated in "VREvent":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/dto/VREvent.java class.
However, there are other types of messages that are not distributed to other clients: commands and their return values, and errors.
Client will typically execute at least one command during the session - "Session":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/dto/Session.java start. It will not receive any messages before that.
Should any server-side exception occur during the session, errors are sent to the client as simple JSON maps.
"WorldManager":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/core/WorldManager.java manages clients and event distribution between them.
A server can host many worlds, i.e. shared spaces. A world contains users and other objects that are shared only within the world. It can be thought of as a chatroom, but mind the difference: being in the same world does not mean that users can see and talk to each other.
Client can enter another world by issuing "Enter":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/dto/Enter.java command.
h3. Ownership and privacy
A class can be annotated as Owned, and all of instances automatically become owned as they are created. An owned object does not receive events from anyone by owner(s). A Client is owned, and nobody but himself can change his name.
On the other hand, a generic VRObject is public, and receives events from anyone. Like a door, anybody can open and close it. But even public objects can have some properties annotated as Owned, that can't be change by anyone but owner.
Fields of a class can be annotated as Private, and their contents will never be published.
"Dispatcher":https://github.com/jalmasi/vrspace/blob/master/server/src/main/java/org/vrspace/server/core/Dispatcher.java takes care of it before property changes are applied, and before they are published to listeners.
h3. Package structure
Package "org.vrspace.server":https://github.com/jalmasi/vrspace/tree/master/server/src/main/java/org/vrspace/server contains only main application class. Under it,
- config package contains server configuration classes that are executed only on server statup
- core is the core of the server
- dto is misnomer that stands Data Transfer Objects, though this package contains all objects that are not shared nor persisted
- obj contains persistent objects, most importantly Client and VRObject
- types are custom types used elsewhere, be it interfaces or annotations
- web is a primitive admin interface, disabled by default