93 lines
6.3 KiB
Markdown
93 lines
6.3 KiB
Markdown
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# Entity tessellation paths
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How each acadrust `EntityType` becomes drawable geometry in OpenCADStudio, and
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whether it passes through the [truck](https://github.com/ricosjp/truck) modeling
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kernel.
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There are **two distinct meanings of "through truck"** in the codebase, and they
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must not be conflated:
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1. **truck B-rep meshing** — the entity is rebuilt as a truck `Shell`/`Solid`
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and triangulated by `MeshableShape::triangulation()`. This is the only path
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that produces filled *mesh* triangles from a kernel.
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2. **truck curve topology** — the entity is expressed as a truck `Edge`/`Wire`/
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`Vertex` and sampled into line segments by truck's `ParameterDivision1D`. It
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touches truck *topology* but never triangulates a surface; the output is a
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polyline.
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Everything else is **direct**: points/segments/triangles are emitted straight
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from the entity's own data without any truck object.
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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 `TruckObject`
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router) and `src/scene/convert/truck_tess.rs` (curve sampling).
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## Summary
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| Path | Entities |
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|---|---|
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| **truck B-rep mesh** (Shell → `triangulation`, with a direct per-surface fallback) | `Solid3D`, `Region`, `Body`, `Surface` |
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| **truck curve topology** (Edge/Wire → `ParameterDivision1D` sampling) | `Line`, `Arc`, `Circle`, `Ellipse`, `Spline`, `LwPolyline`, `Polyline`, `Polyline2D`, `Polyline3D`, `Point` — *non-thick variants only* |
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| **direct** (no truck — segments/triangles emitted directly) | everything else |
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> The Model/Design-tab primitives (BOX, SPHERE, CYLINDER, CONE, WEDGE, TORUS,
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> PYRAMID, extrude/revolve/loft/sweep) are also true truck B-rep meshes
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> (`truck_tess::tessellate_solid`), but they are created as `Solid3D`
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> placeholders carrying a truck B-rep, not as their own `EntityType`.
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The only call site of `shell.triangulation()` for an imported entity is
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`acis_to_truck::tessellate_sat_truck`. The four ACIS solids dispatch through
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`solid3d_tess::tessellate_acis`, which tries that truck kernel first and falls
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back to a bespoke per-surface LOD sampler (`tessellate_sat_lods`) when truck
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cannot rebuild a face — so their path is **truck-with-direct-fallback**.
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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 | direct (truck curve topology) | non-thick: truck `Edge` (`builder::circle_arc`) sampled via `ParameterDivision1D`; thick: direct `Lines` |
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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 | truck-with-direct-fallback | 3D ACIS body → truck `Shell` → `triangulation`; fallback per-surface sampler |
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| Circle | wire | direct (truck curve topology) | non-thick: truck `Wire` of two half-circle edges; 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 | direct (truck curve topology) | truck `Wire`/`Edge` over a `BSplineCurve`, `ParameterDivision1D` sampled |
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| Face3D | both | direct | edge `Lines` + direct fan-triangulated `fill_tris`; no truck 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 | direct (truck curve topology) | non-thick: truck `Edge` (`builder::line`); thick: direct `Lines` |
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| LwPolyline | wire | direct (truck curve topology) | `plinegen` true: truck `Contour` with bulge 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 (truck topology) | truck `Vertex` → 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 | direct (truck curve topology) | heavy 3D polyline; truck `Contour` + bulge arcs |
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| Polyline2D | wire | direct (truck curve topology) | 2D polyline with bulge; truck `Contour` |
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| Polyline3D | wire | direct (truck curve topology) | linear-edge truck `Contour`, no bulge/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 | truck-with-direct-fallback | 2D planar ACIS body; same truck 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 | truck-with-direct-fallback | 3DSOLID: parse SAT/SAB → truck `Shell` → `triangulation`; fallback sampler |
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| Spline | wire | direct (truck curve topology) | NURBS/BSpline truck `Edge`, `ParameterDivision1D` sampled |
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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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