Improve Filament Studio source builds

[devshahofficial]

Summary

This draft improves the experimental Studio + Filament source-build path in two ways:

• prevents Filament's Abseil lookup from discovering unrelated package-manager CMake configs after MuJoCo has already fetched Abseil
• documents a minimal isolated Studio build/run flow, including macOS runtime expectations and troubleshooting for conflicting CMake package prefixes

Motivation

While validating mujoco_studio with MUJOCO_USE_FILAMENT=ON, configure can fail on machines with ambient package-manager CMake configs, for example an Anaconda-provided abslConfig.cmake. Filament's FILAMENT_USE_EXTERNAL_ABSL path calls find_package(absl), which can collide with the Abseil targets already created by MuJoCo's fetched dependency.

This keeps the Filament fetch isolated from unrelated Abseil package configs, while preserving any pre-existing CMAKE_DISABLE_FIND_PACKAGE_absl value after Filament is configured.

Validation

• git diff --check
• fresh CMake configure of Studio + Filament without manually passing -DCMAKE_DISABLE_FIND_PACKAGE_absl=TRUE
• cmake --build build-studio-filament-eval --target mujoco_studio --parallel $(sysctl -n hw.logicalcpu)
• local runtime smoke test:
  • ./mujoco_studio --gfx=opengl --model_file=/tmp/mujoco_go2_demo/unitree_go2/scene_filament_open_assets_showcase.xml
  • runtime log: FEngine resolved backend: OpenGL
  • platform log: Apple M3 Pro, OpenGL reported through Apple's Metal-backed OpenGL layer

Screenshot from the local smoke test:

Related context

Tagging a few people from the surrounding Filament/Studio discussion for visibility:

• @yuvaltassa noted in issue Renderer API #2487 that Studio is close to ready from src/experimental/studio/: Renderer API #2487 (comment). This PR is a small source-build/doc cleanup around that path.
• @BlGene and @wpumacay have related downstream wheel/runtime requirements from the AllenAI/MolmoSpaces work: Renderer API #2487 (comment), Renderer API #2487 (comment), and https://github.com/allenai/mujoco/tree/molmospaces.
• @julien-blanchon has related prior work around Filament builds, wheel asset staging, and runtime asset lookup: Renderer API #2487 (comment) and https://github.com/julien-blanchon/mujoco/tree/exp-filament-build.

Notes

The Go2 / Filament sample-asset scene used for the runtime smoke test is local-only and not included in this PR.

[devshahofficial]

Keeping this PR focused on the Studio source-build path. I opened a separate stacked draft for the packaging/runtime follow-up pieces: generated Filament assets in install/wheels, default runtime asset lookup, and a small renderer identity query surfaced through Python.

Follow-up draft: #3254

That follow-up is still draft because full wheel artifact verification is pending, but I smoke-tested Studio with a Go2 scene on macOS and verified the MJR-compat build exports mjr_getRenderer() returning filament.

[devshahofficial]

Rebased this onto current main and folded in one source-build fix I hit locally: Filament can include base ImGui without forcing the SDL backend, while Studio creates dear_imgui_SDL2 after SDL2 is available. Local git diff --check, Filament configure, and Studio+Filament configure pass. CI is queued now.

[devshahofficial]

Rebased this onto current main and pushed the refreshed branch.

Local validation on the rebased commit:

• git diff --check
• Filament configure with examples/sim/tests off:
  cmake -S . -B /tmp/mujoco-pr3252-filament -DCMAKE_BUILD_TYPE=Release -DUSE_STATIC_LIBCXX=OFF -DBUILD_SHARED_LIB=OFF -DMUJOCO_USE_FILAMENT=ON -DMUJOCO_BUILD_EXAMPLES=OFF -DMUJOCO_BUILD_SIMULATE=OFF -DMUJOCO_BUILD_TESTS=OFF -DMUJOCO_TEST_PYTHON_UTIL=OFF -DMUJOCO_WITH_USD=OFF -DFILAMENT_SKIP_SAMPLES=ON -DFILAMENT_SHORTEN_MSVC_COMPILATION=OFF
• Studio+Filament configure:
  cmake -S . -B /tmp/mujoco-pr3252-studio -DCMAKE_BUILD_TYPE=Release -DUSE_STATIC_LIBCXX=OFF -DBUILD_SHARED_LIB=OFF -DMUJOCO_USE_FILAMENT=ON -DMUJOCO_BUILD_EXAMPLES=OFF -DMUJOCO_BUILD_SIMULATE=OFF -DMUJOCO_BUILD_TESTS=OFF -DMUJOCO_TEST_PYTHON_UTIL=OFF -DMUJOCO_WITH_USD=OFF -DMUJOCO_BUILD_STUDIO=ON -DFILAMENT_SKIP_SAMPLES=ON -DFILAMENT_SHORTEN_MSVC_COMPILATION=OFF -DCMAKE_CXX_FLAGS=-Wno-error=deprecated-declarations

Both configure paths now pass locally, including the Abseil/Filament path and the delayed dear_imgui_SDL2 setup after SDL2 is available. Fresh CI is running now. @haroonq or @yuvaltassa, could one of you take a look when you have bandwidth?

[BlGene]

Hi @devshahofficial,

Of the remaining PRs, is this also the order they should be merged in?

1. Improve Filament Studio source builds #3252
2. Package Filament runtime assets #3337
3. Add packaged asset resource provider #3339
4. Add renderer info query API #3340

[devshahofficial]

@BlGene yeah, that order is the cleanest one imo:

1. Improve Filament Studio source builds #3252
2. Package Filament runtime assets #3337
3. Add packaged asset resource provider #3339
4. Add renderer info query API #3340

Small caveat: #3340 had drifted into conflict, so I rebased it and pushed the fix today. I would still land the Filament stack in that order unless @mmossg / @haroonq prefer a different split.

[devshahofficial]

@BlGene quick extra context for the Ai2 / Filament use case:

• Improve Filament Studio source builds #3252 gets the Filament Studio source-build path cleaned up.
• Package Filament runtime assets #3337 packages the Filament runtime assets.
• Add packaged asset resource provider #3339 adds the mujoco: packaged asset provider.
• Add renderer info query API #3340 adds the renderer info query API, so Python can tell classic vs Filament.

Current state: #3252/#3337/#3339 are green + mergeable. #3340 is rebased, still approved, mergeable again, and just waiting on the last CI jobs.

So yeah, this stack is basically aimed at the exact pain points you listed in #2487. I do not want to overpromise release timing or wheel policy since maintainers own that part, but the code path for packaged assets + renderer query is now lined up.