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The feature existed for one reason: truck's mesh and boolean crates reach `vtkio → xz2 → lzma-sys`, a C library that cannot cross-compile to wasm32. So the web build dropped it, and with it the Model tab, solid tessellation and ACIS import — all of which quietly did nothing in the browser. cadkernel is pure Rust and has no C dependency, so none of that holds any more. The feature gated exactly two things by the end, `acis_export` and the save-path sync that calls it, and both are as portable as everything around them. Removing it means the web build makes primitives, runs booleans, draws ACIS solids read from a file, and writes them back out as exact geometry — the same as the desktop build. Verified against all three: native, `--no-default-features`, and an actual `wasm32-unknown-unknown` check rather than an assumption about one. The docs claimed otherwise in four places and are corrected. `tessellation.md` in particular was organised around whether an entity "goes through truck", which is no longer a question anything can be asked — the three paths are now a kernel B-rep mesh, a curve sampled through `entities::curve`, or geometry emitted directly, and the per-entity table is updated to match. `index.html` no longer passes `data-cargo-no-default-features`; there are no features left to turn off. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
98 lines
6.5 KiB
Markdown
98 lines
6.5 KiB
Markdown
# Entity tessellation paths
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How each acadrust `EntityType` becomes drawable geometry in OpenCADStudio.
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There are **three ways** an entity gets there, and they must not be conflated:
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1. **Kernel B-rep mesh** — the ACIS document is lifted into a cadkernel `Body`
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and each face triangulated in its own surface's parameter space. The only
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path that produces filled *mesh* triangles from analytic surfaces.
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2. **Curve-sampled** — the entity's geometry is read through
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`entities::curve::entity_curve`, which is where each type's curve is defined
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once, and tessellated to a chord tolerance. Output is a polyline; no surface
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is involved.
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3. **Direct** — points, segments or triangles emitted straight from the
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entity's own fields.
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The distinction between (2) and (3) is worth keeping because (2) is a single
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definition shared with everything else that needs an entity's geometry — snap
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candidates, EXTRUDE and REVOLVE profiles, hatch boundaries, clip outlines. A
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circle drawn on screen and a circle handed to the Model tab come from the same
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place and cannot disagree.
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Entry points: `src/scene/convert/tess.rs` (`tessellate_entity`, the per-entity
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dispatcher) → `src/scene/convert/tessellate.rs` (`tessellate`, the
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`RenderObject` router), `src/entities/curve.rs` (curve definitions and
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sampling) and `src/scene/convert/curve_tol.rs` (the per-frame chord tolerance).
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## Summary
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| Path | Entities |
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|---|---|
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| **Kernel B-rep mesh** (lift → per-face triangulation, with a direct per-surface fallback) | `Solid3D`, `Region`, `Body`, `Surface` |
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| **Curve-sampled** (`entity_curve` → chord-tolerance tessellation) | `Line`, `Arc`, `Circle`, `Ellipse`, `Spline`, `LwPolyline`, `Polyline`, `Polyline2D`, `Polyline3D` — *non-thick variants only* |
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| **Direct** (segments/triangles emitted straight) | everything else |
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> The Model/Design-tab primitives (BOX, SPHERE, CYLINDER, CONE, WEDGE, TORUS,
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> PYRAMID, EXTRUDE, REVOLVE) are true kernel B-reps too, cached on the Scene as
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> `Body` and meshed the same way — but they are created as `Solid3D`
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> placeholders carrying that body, not as their own `EntityType`. SWEEP and
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> LOFT produce a mesh only, with no B-rep behind it.
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ACIS solids dispatch through `solid3d_tess::tessellate_acis`, which lifts the
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document into the kernel first (`acis_kernel::tessellate_sat`) and falls back
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to a bespoke per-surface LOD sampler (`tessellate_sat_lods`) when the kernel
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cannot express a face — so their path is **kernel-with-direct-fallback**. The
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fallback is not silent: a mesh whose faces did not all lift is marked
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incomplete, because one missing wall looks exactly like a finished solid.
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Curved-surface tessellation density is radius-relative (`CURVE_REL_TOL`, a
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fraction of the surface radius) so a cylinder's facet count matches the
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circle/arc wire tessellation instead of exploding on large radii.
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## Full table
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| Entity | Output | Path | Notes |
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|---|---|---|---|
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| Arc | wire | curve-sampled | non-thick: sampled from the arc's own curve; thick: direct `Lines` plus the swept wall |
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| AttributeDefinition | wire | direct | routes through the Text/MText LFF glyph stroke pipeline |
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| AttributeEntity | wire | direct | same as AttributeDefinition; values supplied per Insert |
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| Block | none | n/a | block-definition sentinel; not tessellated (referenced via Insert) |
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| BlockEnd | none | n/a | block-definition end marker; no output |
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| Body | mesh | kernel-with-direct-fallback | 3D ACIS body lifted into a kernel `Body`; fallback per-surface sampler |
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| Circle | wire | curve-sampled | non-thick: sampled from the circle's own curve; thick: direct `Lines` |
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| Dimension | wire | direct | baked-block path recurses on `D###` sub-entities; synthesis path emits lines/arrows/LFF text |
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| Ellipse | wire | curve-sampled | sampled from the ellipse's own curve |
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| Face3D | both | direct | edge `Lines` + direct fan-triangulated `fill_tris`; no B-rep |
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| Hatch | both | direct | boundary outline not emitted to the wire set (#131 OOM); fill rasterized on GPU |
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| Insert | wire | direct | expands block children and tessellates each via its own path; XCLIP filter applied |
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| Leader | wire | direct | leader path + arrowhead + landing, direct `Lines` |
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| Line | wire | curve-sampled | non-thick: its two ends; thick: direct `Lines` plus the swept wall |
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| LwPolyline | wire | curve-sampled | `plinegen` true: sampled from its own curve, bulges kept as arcs; else direct `SegmentedLines` |
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| Mesh | both | direct | SubD mesh: edge `Lines` + direct fan-triangulated `fill_tris` |
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| MLine | wire | direct | spine + offset lines + caps, direct `Lines` |
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| MText | wire | direct | wrap-aware multi-line LFF glyph layout; inline formatting codes |
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| MultiLeader | wire | direct | leader + landing + LFF text + frame + fill |
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| Ole2Frame | wire | direct | bounding rectangle + diagonal cross |
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| Point | wire | direct | a position → dot or cross marker sized by PDSIZE |
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| PolyfaceMesh | both | direct | face list: closed-polyline edges + direct fan-triangulated `fill_tris` |
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| PolygonMesh | both | direct | M×N grid wireframe + direct fan-triangulated `fill_tris` |
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| Polyline | wire | curve-sampled | heavy 3D polyline; sampled from its own curve, bulges kept as arcs |
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| Polyline2D | wire | curve-sampled | 2D polyline with bulge; sampled from its own curve |
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| Polyline3D | wire | curve-sampled | straight edges, no bulge or thickness |
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| RasterImage | wire | direct | boundary rectangle / clipping polygon |
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| Ray | wire | direct | two-point `[base, base + dir×1e6]`, no sampling |
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| Region | mesh | kernel-with-direct-fallback | 2D planar ACIS body; same kernel path as Solid3D |
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| Seqend | none | n/a | vertex-sequence terminator sentinel; no output |
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| Shape | wire | direct | small diamond marker at the insertion point |
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| Solid | wire | direct | 2D SOLID: four quad edges as direct `Lines` |
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| Solid3D | mesh | kernel-with-direct-fallback | 3DSOLID: parse SAT/SAB → lift into a kernel `Body`; fallback sampler |
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| Spline | wire | curve-sampled | NURBS sampled through the kernel's space curve, refined where it bends |
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| Table | both | direct | cell fills (`fill_tris`) + LFF cell text + grid lines |
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| Text | wire | direct | LFF-font stroked glyph polylines |
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| Tolerance | wire | direct | feature-control frame grid + per-cell LFF symbols |
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| Underlay | wire | direct | boundary rectangle of the PDF/DWF reference |
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| Unknown | none | n/a | unrecognized-entity sentinel; no output |
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| Viewport | wire | direct | content-viewport frame rectangle (sheet viewport skipped) |
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| Wipeout | wire | direct | boundary rectangle / clipping polygon |
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| XLine | wire | direct | three-point infinite line, no sampling |
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