Add TrCommandBufferManager for renderer-side WebGPU command encoding

[Copilot]

Implements a thread-safe manager that accepts TrCommandBufferBase instances from the content process, dispatches them by type to GPUDeviceBase, and stores encoded WebGPU command buffers for flexible host renderpass submission.

Implementation

Core Components (src/renderer/command_buffer_manager.{hpp,cpp} - 551 lines)

• TrCommandBufferManager class with mutex-protected storage
• EncodedPass structure storing command buffers + XR routing metadata (sessionId/stereoId/viewIndex)
• Type-based dispatch using CommandTypes helpers (framebuffer/resource/generic paths)
• Encoding stubs with TODO markers referencing WebGPU spec sections

Unit Tests (tests/command_buffer_manager.cpp - 109 lines)

• API surface validation, command classification, thread safety

Documentation (643 lines)

• WebGPU implementation gap analysis with priority ranking
• Usage examples (basic, XR multi-view, frame lifecycle)
• Architecture overview and integration notes

Usage

auto manager = std::make_unique<TrCommandBufferManager>(device);

// Thread-safe command addition
manager->addCommandBuffer(std::move(cmd));

// Host render loop
const auto& passes = manager->getEncodedPasses();
for (const auto& pass : passes) {
  if (pass.isXRPass) {
    submitToXRView(pass.renderingInfo.viewIndex, pass.commandBuffer.get());
  } else {
    submitToMainPass(pass.commandBuffer.get());
  }
}
manager->clearEncodedPasses();

Current State

API complete - all public methods implemented with error handling
Encoding deferred - stubs return nullptr with detailed TODO comments and WebGPU spec references
JSAR's WebGPU layer incomplete - missing copy operations, bind groups, texture APIs documented in docs/webgpu-implementation-status.md

Each encoding path (encodeFramebufferCommand, encodeResourceCommand, encodeGenericCommand) contains:

• Implementation steps
• WebGPU spec section links
• FIXME markers for missing dependencies
• GLES-to-WebGPU translation notes

Integration Notes

• XR routing: Use pass.renderingInfo to determine target view
• Resource lifecycle: Call clearEncodedPasses() after GPU submission completes
• GLES translation: State management mapping needed (bind groups from texture bindings, uniforms aggregation)
• Missing GPUDeviceBase APIs documented with priorities in status doc

Original prompt

Implement a renderer-side class TrCommandBufferManager that accepts TrCommandBufferBase instances, dispatches them by type to the project’s GPUDeviceBase API to encode them into "passes" (platform / WebGPU encoded command buffers or byte blobs), and exposes the encoded passes for later host renderpass submission.

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Background / Motivation

The runtime receives serialized command buffers (TrCommandBufferBase). The renderer needs a component that converts those command buffers into encoded WebGPU commandbuffer which can be submitted later under different host render passes (such as host opaque pass, transparent pass or offscreen pass). The repository already contains TrCommandBufferBase and helpers (e.g., CommandTypes::IsFramebufferDependentCommand).

Important: the current JSAR WebGPU implementation is incomplete and not production-ready. To implement correct encoding behavior you must consult the WebGPU specification and align the implementation with the spec. In JSAR:

• The general WebGPU interface definitions live under src/common/commandbuffers/gpu
• The GLES concrete implementation lives under src/renderer/gles/gpu_*

This task requires reading the WebGPU spec and supplementing/implementing the missing parts of JSAR’s WebGPU implementation in src/common/commandbuffers/gpu and, where necessary, adding renderer-side glue to src/renderer/ so that TrCommandBufferManager can use webgpu::GPUDeviceBase to perform encoding.

Why encoding to WebGPU commandbuffer?

Because WebGPU commandbuffer is free to be submitted multiple times, and can be recorded ahead of time. This allows the host to schedule rendering more flexibly, and also allows reusing encoded commands across frames if the scene is static.

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Scope / Acceptance Criteria

• Add related source files to src/renderer/:
• TrCommandBufferManager must:
  • Be constructible with webgpu::GPUDeviceBase*
  • Provide:
    • void addCommandBuffer(std::unique_ptr<commandbuffers::TrCommandBufferBase> cmd)
      • Inspects cmd->type, dispatches encoding (framebuffer/resource/generic) and enqueues an EncodedPass
      • Thread-safe
    • a method that returns encoded passes which can be submitted later by the host.
    • a method to clear stored encoded passes
  • Use commandbuffers::CommandTypes helpers to decide dispatch branches
  • Contain clear TODO / FIXME notes where GPUDeviceBase real API calls must be plugged in
• Thread-safety: modifying encoded storage must be guarded (e.g., std::mutex)
• WebGPU completeness: PR must include concrete changes to JSAR’s WebGPU layer where required (in src/common/commandbuffers/gpu) so TrCommandBufferManager can meaningfully call into webgpu::GPUDeviceBase. Add well-documented TODOs if some parts are intentionally deferred, and reference specific WebGPU spec sections used to design the implementation.

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Integration notes / TODOs

• Read the WebGPU specification and ensure the encoding semantics implemented match the spec (command encoding, render passes, resource creation lifetimes, synchronization rules, etc.). Document which spec sections were consulted in PR description or code comments.
• Replace forward declarations with the real GPUDeviceBase include once known (e.g., #include "webgpu/GPUDeviceBase.hpp").
• Replace pseudocode device_->Encode* calls with real API calls that align with the WebGPU semantics implemented in JSAR.
• Consider changing EncodedPass::rawEncodedCommands to store platform-specific objects (e.g., GPUCommandBuffer handles). If GPU handles are non-copyable, use shared_ptr/unique_ptr semantics and update getEncodedPasses() accordingly.
• Ensure GPU resource lifecycle management matches the rest of the project (release on clearEncodedPasses() or after host signals completion).
• For XR: ensure pass routing uses pass->renderingInfo (sessionId/stereoId/viewIndex) so host can place the pass into correct host renderpass.
• Where JSAR’s src/common/commandbuffers/gpu lacks functionality, add minimal, spec-aligned implementations (and unit-tests if feasible) rather than leaving only renderer-side placeholders.

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Example snippet (usage)

Just to illustrate how TrCommandBufferManager works, please design the API by yourself. Here is a pseudocode example:

// create manager (device is your webgpu::GPUDeviceBase*):
auto manager = std::make_unique<renderer::TrCommandBufferManager>(device);

// feed command
manager->addCommandBuffer(std::move(cmd));

// later in host render loop:
auto passes = manager->getRenderPasses();
for (auto& pass : passes) {
  // host submits pass (platform-specific)
  host->submitEncodedPass(*pass);
}
manager->clearEncodedPasses();

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