Three.js WebGPU Client — Stage 2: Player

Supersedes: 20260425-threejs-webgpu-zone-client.md (split) Requires: 20260425-threejs-observer.md

Superseded by: 20260425-godot-player.md

Status: superseded
Deciders: V-Sekai, fire
Tags: V-Sekai, Threejs, WebGPU, WebTransport, Player, ZoneServer, libriscv, taskweft, WebXR, 20260425-threejs-player

The Context

Stage 1 (20260425-threejs-observer.md) delivers a read-only browser observer. Stage 2 adds entity control, GDScript behavior via libriscv WASM, RECTGTN planning via taskweft WASM, and VR presence via WebXR.

The Problem Statement

The observer cannot send entity input or run behavior scripts. An operator who wants to interact with entities (spawn jellyfish, trigger behavior changes, enter VR) needs the player layer.

Design

CH_PLAYER write path

function sendPlayer(wt: WebTransport, entityId: number, payload: Uint32Array): void {
  const buf = new ArrayBuffer(100);
  const view = new DataView(buf);
  view.setInt32(0, entityId, true);
  // ... fill position, velocity, payload fields
  wt.datagrams.writable.getWriter().write(new Uint8Array(buf));
}

GDScript behavior via libriscv WASM

The ELF is compiled once and stored in the CDN. vm_deterministic in WasmEquiv.lean proves the VM produces the same result on any host:

GDScript  → RISC-V ELF   (compile once; CDN asset)
libriscv  → WASM          (Emscripten; browser loads VM, feeds it the ELF)

The integration risk is the godot-sandbox guest ABI: the syscall shim mapping RISC-V ecall to Emscripten host calls. This must be verified before Stage 2 ships.

RECTGTN planning via taskweft WASM

standalone/tw_planner.hpp is header-only C++20 with no BEAM dependency. It compiles directly to WASM via Emscripten and runs the same species domain JSON-LD files that drive the native zone server. Emscripten build constraints (no dynamic linking, POSIX subset) must be verified.

VR presence via WebXR

renderer.xr.enabled = true;
document.body.appendChild(VRButton.createButton(renderer));

The Godot XR layer is not required. Three.js WebXR handles headset rendering.

The Downsides

libriscv WASM ABI shim and taskweft Emscripten build are unverified. Shipping Stage 2 before these are tested risks a broken browser VR experience.

The Road Not Taken

Godot native PCVR client handles high-fidelity VR and is the reference implementation. Stage 2 is the browser peer; it does not replace the native client.

Status

Status: Superseded by 20260425-godot-player.md. Not being built.

Decision Makers

iFire