oxideav-mesh3d 0.0.5

Pure-Rust 3D scene + mesh typed model — Decoder/Encoder traits for STL/OBJ/glTF/FBX/USD format crates
Documentation

oxideav-mesh3d

CI crates.io docs.rs License: MIT

Pure-Rust 3D scene + mesh typed model.

The shared data model that every OxideAV 3D-format crate (oxideav-stl, oxideav-obj, oxideav-gltf, oxideav-usdz, oxideav-fbx) decodes into and encodes from. The type model is aligned with glTF 2.0 (Khronos KHR-public spec) as the spec-stable common denominator: right-handed coordinates, Y-up, -Z forward, metres, metallic-roughness PBR, xyzw quaternions. Files coming from Z-up formats (STL/OBJ Wavefront) set [Scene3D::up_axis] to Axis::PosZ — the model stores the orientation, no implicit re-projection happens.

This crate carries no format parsers of its own; sibling crates plug their decoders/encoders into [Mesh3DRegistry] (or use oxideav-meta::populate_mesh3d_registry). Cross-format roundtrip coverage lives in the workspace umbrella's oxideav-tests.

Type model

  • Scene3D — top-level container holding arenas of nodes, meshes, materials, textures, skeletons, skins, animations, cameras, lights, audio sources/emitters, plus up_axis / front_axis / unit metadata and a free-form extras round-trip side-channel. Scene3D::append splices another scene's every arena onto the end of this one's, rewriting all internal ids (node↔mesh↔material↔texture, skin↔skeleton↔joint-node, animation-target nodes, audio emitter↔source) so the relocated resources still reference each other — the primitive behind multi-file import / instancing — returning an AppendOffsets recording where each source arena landed. Material::map_texture_ids remaps every texture slot (core + all extensions) in one call.
  • Node + Transform { Matrix, Trs } with matrix↔TRS decompose, plus a per-instance morph-weight override (Node::weights, glTF node.weights) — two nodes sharing one mesh can hold different static blend states; Scene3D::effective_morph_weights resolves the static (node > mesh) half of the weight-precedence chain and validate enforces the count/mesh-presence rules.
  • Mesh / Primitive / Topology (Triangles, TriangleStrip, TriangleFan, Lines, LineStrip, LineLoop, Points) / Indices (U16 or U32). Multi-channel UVs, vertex colours, optional skinning joints + weights, and MorphTarget delta buffers.
  • Material — full glTF 2.0 metallic-roughness PBR slots plus AlphaMode and double_sided, refined by a typed MaterialExt surface for the KHR material extensions: emissive strength, index of refraction, dispersion, Specular (strength + F0-colour factors and textures), the unlit flag, and seven layered refinements — Clearcoat, Sheen, Transmission, DiffuseTransmission, Volume, Iridescence, Anisotropy. Each field is Option/flag- shaped so an absent extension stays distinguishable from its spec default; effective_ior() / effective_emissive_strength() / effective_dispersion() / Volume::effective_attenuation_distance() substitute the default on demand, and dielectric_f0() / dielectric_f0_rgb() / rgb_iors() evaluate the spec-documented IOR/specular/dispersion combination formulas. This surface covers every input of USD's UsdPreviewSurface (specular workflow, clearcoat + clearcoat roughness, IOR, opacity threshold via AlphaMode::Mask) so format importers keep extras for genuinely exotic parameters only. Material::texture_refs() enumerates every occupied texture slot (core + all extensions) for resource walkers, and is what Scene3D::validate checks texture ids through.
  • Texture references (TextureRef) — texture id + UV set + an optional typed TextureTransform (KHR_texture_transform: offset / rotation / scale plus the texCoord override), None keeping "no transform declared" distinguishable from an explicit identity. The transform carries its semantics typed: to_matrix (row-major T·R·S), apply / apply_channel (the whole-channel bake an exporter targeting a transform-free format needs), is_identity / is_finite; TextureRef::effective_uv_set resolves the override chain. Material::map_texture_refs rewrites whole references across every slot in one walk (uv-set retargeting, transform attach/clear); map_texture_ids stays the id-only remap. Scene3D::validate enforces transform finiteness and the UV-set coverage rule — every texture slot of every material a primitive can draw with (base + variant mappings) must sample a UV channel that primitive carries, checked through the effective (override-aware) set.
  • Material variants (KHR_materials_variants) — Scene3D::material_variants name roster + per-primitive VariantMapping overrides. append unifies rosters by name, merge_primitives_by_material treats mappings as draw state, and validate enforces live ids plus the at-most-once variant rule.
  • Texture / ImageData { Embedded, Source(Arc<dyn AssetSource>), External } / Sampler. The sampler keeps glTF's undefined-filter state representable (Option-shaped mag/min filters — the spec gives them no default — with effective_* accessors substituting the documented Linear / trilinear fallback), decomposes mip behaviour (MinFilter::mipmap_mode → MipmapMode, uses_mipmaps, base_filter), and evaluates the wrap modes' reference semantics (WrapMode::wrap, Sampler::wrap_uv; wraps default to the normative Repeat). AssetSource lets format crates pass a lazy reader through the model without materialising bytes, with optional raw_storage() pass-through for archive-to-archive copy.
  • Skeleton + Skin; Animation / channels / samplers / Interpolation; Camera; Light; Audio* types (AudioSource, AudioEmitter, SpatialAudio, AuralMode, DistanceModel).
  • Mesh3DDecoder / Mesh3DEncoder traits + Mesh3DRegistry (case-insensitive extension / format-id lookup).

Geometry reductions

The crate ships a large pure-Rust geometry toolkit on Primitive (lifted to Mesh / Scene3D where additive). All reductions are pure (no mutation), robust (out-of-range / degenerate / NaN inputs are skipped or fall back rather than panic), and topology-aware (strips/fans feed through triangle_indices):

  • Connectivity — triangle_indices, to_triangle_list, weld_vertices, triangle_adjacency, degenerate_triangles, boundary_edges, boundary_loops, edge_manifold_report / is_closed_manifold, topology_summary (V/E/F, Euler characteristic, component count, orientable genus), orient_consistent (flood-fill the face-dual graph to repair mixed-winding facet soup into per-component coherent winding, returning the re-oriented faces + an OrientationReport), fill_holes (cap every boundary loop with a Newell-projected ear-clip patch wound consistent with the surrounding surface, making a torn surface watertight again).
  • Attributes — compute_normals (area-weighted), compute_tangents (MikkTSpace-style basis), apply_morph_weights, and the static-fold lifts Primitive::morphed / Mesh::morphed (blend the weight vector in, consume the target roster — the flatten a morph-free target format needs).
  • Measures — surface_area, surface_centroid, signed_volume / volume, volume_centroid (centre of mass), inertia_tensor (unit density). Each has Mesh / Scene3D rollups and transform-folding world_* variants (world_surface_area, world_surface_centroid, world_signed_volume, world_volume_centroid, world_inertia_tensor).
  • Curvature — Primitive::curvature returns a CurvatureReport carrying per-vertex discrete Gaussian curvature (Gauss-Bonnet angle defect 2π − Σθ / π − Σθ on boundary, normalised by the mixed Voronoi area), mean curvature (½‖Δp‖ from the cotangent Laplace-Beltrami operator), and the per-vertex mixed area itself — parallel to the welded vertex pool (also returned). The discrete Gauss-Bonnet identity Σ defect = 2π·χ holds to machine precision on closed meshes (total_angle_defect exposes it as a cheap topological check), and the mixed areas sum to the surface area exactly. The signal feeds feature-preserving decimation, adaptive remeshing, and decoded-mesh quality metrics.
  • Scene graph — world_node_transforms, world_node_bounds, bounding_box. Navigation + flattening: Scene3D::parents (first-parent spanning-forest map), ancestors (root→parent chain), descendants (DFS subtree incl. self), is_ancestor_of, and Node::local_matrix. Scene3D::bake_transforms collapses the hierarchy into a flat root list — every reachable node carries its full world matrix as Transform::Matrix with cleared children, node indices preserved, draws identically — exactly what a hierarchy-free target (STL/OBJ) needs. All navigation shares the first-arrival DFS semantics of world_node_transforms.
  • Ray queries — Ray / RayHit, ray::intersect_triangle (Möller-Trumbore) / intersect_aabb (slab), Primitive:: intersect_ray / any_ray_intersection, an object-median per- primitive Bvh, a scene-level InstanceBvh, and a world-space Scene3D::intersect_ray returning SceneRayHit.
  • Geometry transform — Primitive::transformed(m) / Mesh::transformed(m) bake an affine 4×4 into the vertex data: positions move by the full affine, normals by the inverse-transpose of the linear part (so they stay perpendicular to the surface under non-uniform scale), tangent directions by the linear part with handedness w flipped on a mirroring (negative-determinant) transform; a singular linear part leaves normals untouched but still moves points. Primitive::reverse_winding flips triangle orientation (swap two corners, negate normals, invert tangent w) for importing clockwise / left-handed sources. The vertex-data complement to Scene3D::bake_transforms — together they let an exporter flatten into a transform-free, hierarchy-free target.
  • Consolidation — Primitive::merge concatenates two primitives into one indexed Triangles primitive, re-basing the second's indices onto the end of the first's vertex pool and reconciling optional attributes by union with spec-neutral fill (an attribute present on either input survives; the side that lacked it gets a default row — [0,0,1] normal, white colour, origin UV, …). UV/colour set counts take the max; morph deltas are dropped. Mesh::merge_primitives_by_material partitions a mesh's primitives by their material reference (with the unmaterialled None group kept separate) and fuses each group, collapsing an N-primitive mesh to at most one draw call per distinct material — the standard batching / pre-compression pass for an OBJ-g-split or per-accessor glTF import.
  • Polygon triangulation — Primitive::from_polygons(positions, faces) builds an indexed Triangles primitive from a shared vertex pool plus a list of n-gon faces (each an index list), triangulating every >3-corner face with the same Newell-projected ear-clip fill_holes uses — so concave and non-planar faces are handled correctly (a naïve fan would self-overlap). The bridge from the polygon-face formats (OBJ f, FBX/USD face lists). Vertex indices are preserved (no welding/reorder) so the caller can attach its own attribute buffers afterward; each n-gon yields n−2 triangles inheriting the face's winding; out-of-range / degenerate faces are skipped.
  • Parametric solids — extrude::Profile2D with ear-clip triangulate and watertight extrude.
  • Refinement — subdivide_loop (one step of Loop subdivision): welds, splits every triangle 1 → 4, places interior edge vertices with the 3/8·(A+B) + 1/8·(C+D) mask / boundary edge vertices at the midpoint, and relaxes original vertices (interior Warren β, boundary cubic-B-spline mask). Positions carry the Loop masks; all other attributes (normals/tangents/UVs/colours/joints/weights/morph deltas) are linearly interpolated. Boundaries stay watertight; iterate for a smooth limit surface from a coarse STL/OBJ/CSG cage.
  • Fairing — smooth_laplacian(lambda, opts) relaxes every vertex a fraction λ of the way toward its one-ring centroid (the uniform umbrella Laplacian vᵢ' = vᵢ + λ·(centroid(N(i)) − vᵢ)), a Jacobi sweep so the result is order-independent; smooth_taubin(lambda, mu, opts) alternates a positive shrink pass with a negative inflate pass (μ < −λ < 0) for the same noise removal without the volume shrinkage of the plain Laplacian. Both weld first, preserve the connectivity exactly (only positions move; all other attributes pass through), pin boundary vertices by default (SmoothOptions::preserve_boundary), and skip any vertex whose smoothed position would be non-finite.
  • GPU vertex-buffer optimisation — three storage-only reorderings that leave the rendered result exactly invariant (they permute order, never geometry) and double as the recommended pre-processing for index/vertex stream compression. simulate_cache / cache_stats simulate a FIFO post-transform vertex cache and report ACMR (misses / triangles) + ATVR (misses / vertices) so every reorder is measurable. optimize_vertex_cache greedily reorders triangles to maximise post-transform vertex reuse (cache-recency + low-valence scoring, near-linear, pool untouched). optimize_vertex_fetch relabels the vertex pool into index-stream first-appearance order so the pre-transform attribute fetch sweeps the buffer front-to-back (lossless: unreferenced vertices kept). optimize_vertex_spatial(bits) sorts the pool along a Morton (Z-order) curve for non-indexed / seam-heavy meshes where there is no reused index order to follow. Recommended pipeline: optimize_vertex_cache().optimize_vertex_fetch().
  • Decimation — two reducers, both duals of subdivide_loop:
    • simplify_cluster(grid) lays a cube grid (grid cells along the longest bounding-box axis, equal cell edge on every axis), collapses every vertex sharing a cell to one per-cell averaged representative, and re-emits the de-duplicated connectivity over the occupied cells — dropping triangles that no longer span three distinct cells and pruning orphan cells. All attributes are averaged per cell (normals / tangent xyz re-normalised, tangent w by cell-majority handedness, weights re-normalised to sum 1, joints carried verbatim). Unconditionally robust (no legality tests) but position-quantising.
    • simplify_quadric(target_triangles) is the error-optimal counterpart: each vertex accumulates the sum of the fundamental error quadrics (Kp = p·pᵀ) of its incident triangle planes, and a greedy min-heap collapses the edge whose merged residual v̄ᵀ Q̄ v̄ is smallest, re-positioning the survivor at the error-minimising point (solved from the 3×3 quadric sub-block, endpoint/midpoint fallback when singular). A fold-over guard rejects collapses that would flip or sliver a triangle; a boundary lock + per-seam constraint quadric keep open silhouettes; non-manifold and link-condition-violating edges are left intact. Position is metric-driven; other attributes blend the endpoints at the optimal split (same conventions as subdivide_loop). ~O(E log E); far truer to the original shape at a given triangle budget than clustering. simplify_quadric_error(max_error) is the error-bounded companion — it stops when the cheapest remaining collapse would exceed a squared-distance budget instead of a triangle count, so the surface never deviates past the budget at any step (0.0 does only coplanar collapses). Both yield a coarser indexed Triangles proxy for level-of-detail or a cheap collision hull; robust against degenerate / non-finite / non-triangle input; neither mutates self. simplify_quadric / simplify_quadric_error additionally lift to Mesh roll-ups that reduce every primitive independently to the same per-primitive budget.

Rigging & animation evaluation

The runtime half of the Skeleton/Skin/Animation type model — glTF 2.0 §3.7.3 (skins), §3.6 + Appendix C (animation), §3.7.4 (instantiation), all pure and rest-scene-preserving:

  • Joint matrices — Scene3D::joint_matrices(node) builds the skinning palette globalTransform(joint) · inverseBindMatrix per joint of the skin bound to a node; the skinned-mesh node's own transform is ignored (§3.7.3.2), so deformed vertices land directly in scene world space. Empty IBM list ⇒ identity per joint; extra trailing IBMs conforming (§3.7.3.1 count ≥ joints), fewer malformed. joint_matrices_with(node, worlds) runs against caller-supplied (shared or posed) world matrices.
  • Linear-blend skinning — Primitive::skinned(palette) / Mesh::skinned(palette): per-vertex M = Σ wᵢ·palette[jᵢ]; positions by the blended affine, normals by its per-vertex inverse-transpose (renormalised, singular ⇒ untouched), tangents by its linear part with handedness flipped on mirroring blends. Invalid influences contribute nothing; all-zero-weight vertices keep rest pose; weights used as stored. normalize_joint_weights() (both levels) is the explicit repair — clamp negatives/NaN to 0, renormalise rows to sum 1, keep all-zero rows — making skinning invariant to uniform weight scaling. validate() reports out-of-range joints (per node→skin→skeleton binding), negative/non-finite weights, and IBM shortfalls.
  • Pose evaluation — Animation::sample_pose(t, n) evaluates every channel per Appendix C (clamp / Step / Linear-SLERP / cubic Hermite) into a sparse Pose (per-node T/R/S + morph-weight overrides), renormalising rotations per the C.5 note. Pose::local_transform merges overrides component-wise into rest TRS; Scene3D::posed_node_transforms(&pose) walks posed world matrices with the world_node_transforms contract. Animation::duration().
  • Skin root — Scene3D::skin_root(skin): the explicit Skin::root_node when stored, else the lowest common ancestor of the joint set over the first-parent spanning forest (§3.7.3.2's documented fallback); pairs with descendants for one-subtree rig culling.
  • Instantiation — Scene3D::world_mesh(node) bakes the §3.7.4 pipeline (static morph weights folded in — the node's override, else the mesh's defaults — then skin-or-transform) into one static world-space mesh; world_mesh_at(anim, t, node) is the animated frame (the full animation > node > mesh weight precedence); Scene3D::posed(anim, t) bakes a whole frame into a scene copy for exporter flattening, writing sampled morph weights onto each driven node so shared meshes keep divergent blend states. Broken palettes yield None, never a silent rigid fallback.

Sketch

use oxideav_mesh3d::{Mesh, Primitive, Topology};

let mut prim = Primitive::new(Topology::Triangles);
prim.positions = vec![[0.0, 0.0, 0.0], [1.0, 0.0, 0.0], [0.0, 1.0, 0.0]];
prim.normals = Some(prim.compute_normals());
let mesh = Mesh::new(Some("tri".to_owned())).with_primitive(prim);

Standalone build

oxideav-core is gated behind the default-on registry cargo feature. Drop the framework dependency entirely with:

oxideav-mesh3d = { version = "0.0", default-features = false }

The typed model and trait definitions stay available — only the embedded-frame ImageData / AudioData variants and the Mesh3DRegistry glue are feature-gated, and Error / Result resolve to a crate-local enum instead of oxideav_core::Error.

License

MIT — see LICENSE.