# W-074 Status

status: in_progress  
task: 编译并复用 Blender Decimate 实现

`web_engine_decimate.cpp` now wraps Blender's native BMesh decimate entry points
(`BM_mesh_decimate_collapse`, `BM_mesh_decimate_unsubdivide` and
`BM_mesh_decimate_dissolve`) behind the local `web_engine_decimate_apply`
two-pass C ABI. The wrapper accepts triangle buffers, returns required output
capacities on the first call, and leaves the input mesh untouched.

`web_engine_apply_command` now accepts `decimateMesh` with a versioned
`SimplifyProfile`, validates the source revision, calls the native wrapper, and
replaces the evaluated SceneIR mesh topology. The command allocates output from
the input upper bounds and evaluates Decimate once; it does not run the
modifier twice merely to query exact capacities. Normals are recomputed from
the result, BMFace material indices are retained, and UV/float-color corners
are transferred by the W-076 policy layer. Collapse now accepts boundary and
non-manifold triangle meshes through the same BMesh bridge. The blend reader
reconstructs corner vertices from `.corner_edge` and `.edge_verts` only after
validating every face cycle, so it never treats edge indices as vertex indices.
`npm run test:topology-collapse` independently opens and collapses an open quad,
an open n-gon and a three-face shared-edge mesh; malformed cycles remain
`summary-only`.

The WebEngine CMake target exports the ABI symbol and links a small archive-file
group containing Blender BMesh, CustomData-capable BKernel objects, DNA/BLO,
local zlib/zstd and allocator support; this avoids pulling the desktop
editor/image dependency graph into the WASM module.

The local artifact is installed in both `web/app/public/vendor/blender/` and
`web/app/src/vendor/blender/`, with the manifest SHA-256 updated. The native
smoke covers all three modes, Collapse topology reduction, revision sequencing,
SceneDelta and normal/UV/material attribute lengths. The browser regression
suite covers the same local WASM command path, including native command,
preview and isolated LOD workers. Modifier-stack transactions and full
skin/seam/sharp preservation remain W-075/W-076.