Update VR README

Author: skim0119

VR/README.md

@@ -7,7 +7,18 @@ Deployment model:
   - Headgear client opens HTTPS URL in Quest Browser.
   - Object-publisher client connects to WSS URL from Python CLI.
 
-## Quick start
+## Join the VR environment
+
+Before joining, use the top-right panel:
+- Choose `Character` (`Demo-spline`, `Two CR`, ...).
+- Click `Join Field`.
+    - You can join as a spectator by clicking `Join as Spectator`.
+    - You can joint arm camera view by clicking `Join Arm Camera`.
+- Click `Enter VR` to enter the VR environment.
+    - This will start the VR session.
+- If you are using a headgear, you can click `Enter VR` on the bottom to enter the immersion mode.
+
+## Quick Setup
 
 Use `npx` or `bunx`, depending on your preference.
 
@@ -20,4 +31,65 @@ Serve the WebXR client over HTTPS:
 npx serve client -l 8443 --ssl-cert certs/dev-cert.pem --ssl-key certs/dev-key.pem
 # or
 bunx serve client -l 8443 --ssl-cert certs/dev-cert.pem --ssl-key certs/dev-key.pem
-```
+```
+### Start runtime server
+
+> This requires a python environment with all packages installed.
+
+```bash
+./VR/scripts/start_server.sh
+```
+
+### Open on Quest Browser (replace `YOUR_SERVER_IP` to your IP or domain name):
+
+> Note: You can also open the client URL in your browser.
+> I have not tested, but some VR immerse emulator plugin exists.
+
+```text
+https://YOUR_SERVER_IP:8443/
+```
+
+The client now auto-derives websocket endpoint from page host:
+- `https://HOST:8443` -> `wss://HOST:8765`
+- `http://HOST:...` -> `ws://HOST:8765`
+
+> You can still override with `?ws=...` or custom port via `?ws_port=...`.
+
+## Character modes:
+
+- `Demo-spline`: current spline demo behavior.
+- `Two CR`: always 2 arms, base is fixed near body center, and base movement controls are disabled. Controller targets are sent to the server, and the server runs `PyElastica` to compute the rod posture.
+
+## Python mesh publisher (remote LAN machine)
+
+Another machine on the same LAN (for example a Macbook) can publish mesh/scenery files into the shared VR scene by connecting to the Linux host WSS URL.
+
+> TODO
+
+1. Install python-packages on the publisher machine.
+2. Run:
+
+
+## System diagram
+
+```mermaid
+flowchart LR
+    subgraph L["Linux Desktop (Server Host)"]
+      C["HTTPS static client :8443"]
+      W["Virtual Field runtime :8765 (WSS)"]
+      E["Simulation backend (PyElastica in physics-driven modes)"]
+    end
+
+    Q["Quest / web browsers"]
+    P["Python publisher clients"]
+
+    Q -->|"Open client page (see Quick Setup; may be / or /client/)"| C
+    Q -->|"hello; then xr_input"| W
+    W -->|"scene_state (periodic broadcast); hello_ack + asset_manifest on join"| Q
+
+    P -->|"hello(role=publisher); mesh / overlay / etc."| W
+    W -->|"mesh_ack, overlay_ack, etc."| P
+
+    W -->|"teleop / step"| E
+    E -->|"arm state, meshes, overlays"| W
+```