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ColorVisuals meshes export without a glTF material, so three.js renders them fully opaque. Convert semi-transparent meshes to texture visuals with a PBR BLEND material on a copy; opaque meshes keep the legacy path. Fixes viser-project#525.
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Fixes #525.
Motivation
SceneApi.add_mesh_trimesh()silently drops transparency: a trimesh mesh with RGBA vertex/face colors (alpha < 255) renders fully opaque in the viewer. Maintainer diagnosis on the issue (root cause: trimesh's GLB exporter emits nomaterialsentry forColorVisuals, so the three.js loader falls back to an opaque standard material; upstream mikedh/trimesh#2436 still open) plus a multi-step manual workaround. This PR applies that workaround automatically, inside viser, so the repro from #525 just works.Changes
src/viser/_scene_api.py: new_trimesh_with_transparency()helper, wired into bothadd_mesh_trimesh()andadd_batched_meshes_trimesh()(same export path, same bug). When semi-transparent colors are present it exports a copy converted to texture visuals with a PBRBLENDmaterial; the caller's mesh is never mutated. Fully opaque meshes return as-is, keeping the export byte-identical. Graceful fallbacks (legacy opaque path) when the trimesh version lacks the PBR API or Pillow is missing for texture baking (with a warning pointing at Pillow).tests/test_trimesh_compatibility.py: 3 regression tests — wire-level test asserting the queued GLB payload carriesalphaMode: BLENDplus caller non-mutation; opaque mesh keeps the material-free export; unit test for the vertex-color path and opaque identity.Verification
materialsin export); post-fix the texture PNG carries the exact alpha (76) and material isBLEND.tests/test_trimesh_compatibility.py+tests/test_strict_copy_on_add.py: 6 passed;test_docs_coverage.py+test_scene_tree.py: 10 passed.ruff check,ruff format --check,pyright: all clean (0 errors).