animsmith_fbx/

lib.rs

//! [`load_source`] and [`load_source_bytes`] retain bounded importer-sensitive
//! source facts beside the normalized [`animsmith_core::Document`] produced
//! from the same exact FBX bytes. [`load`] and [`load_bytes`] remain the
//! document-only compatibility APIs and deliberately discard that immutable
//! sidecar. Parser and projection errors are normalized into [`LoadError`].
//!
//! The loader normalizes FBX scenes into animsmith's runtime-oriented
//! coordinate space before handing them to `animsmith-core`: right-handed
//! +Y-up axes, metres, transform-adjust conversion, helper nodes for
//! geometric transforms, and compensated scale inheritance. Depend on this
//! crate only when your pipeline accepts FBX input; it brings the bundled
//! `ufbx` C build that `animsmith-core` and `animsmith-gltf` intentionally
//! avoid.
//!
//! The source-facts boundary is deliberately narrower than raw FBX bytes.
//! Effective units, signed axes, FPS, take ranges, layer/property bindings,
//! and component-curve presence are parser-projected from ufbx. Advisory
//! `OriginalUnitScaleFactor`/`OriginalUpAxis` values are not substituted for
//! the effective settings. Because animation stacks pass through
//! `ufbx::bake_anim`, the sidecar never claims authored interpolation, keys,
//! or tangents from baked tracks. Resource rows retain bounded relative
//! declarations only; unsafe spellings are classified and redacted, and no
//! dependency is opened solely to build source facts.
//!
//! [`load_scale_source`] and [`load_scale_source_bytes`] retain a typed
//! [`FbxScaleCapabilityInventory`] from the same parse. It gives every current
//! Appendix D.4 domain an explicit status and records baked curves, normalized
//! transforms, derived binds, truncated/renormalized influences,
//! triangulation, welding, generated data, and unavailable raw-span proof.
//! [`capability_facts`] remains the conservative generic refusal projection.
//! [`rest_bind_capability_facts`] admits only the complete normalized subset
//! used by the CLI's narrow FBX rest/bind path: it stages a new GLB, proves
//! that emitted GLB, and never claims raw FBX preservation. Its source-aware
//! companion admits material shader metadata, enumerated scale-invariant
//! conversion-fidelity facts such as triangulation, exact welding, retained
//! effective skinning, and omitted face/edge payload, and only those BindPoses
//! whose converted rows reconcile with the cluster/node matrices consumed by
//! that bridge. [`require_clip_track_capability_for_source`] keeps the same raw
//! construct and animation/hierarchy checks while projecting away geometry,
//! deformation, material, camera/light, and bind domains that a clip-only
//! assembly input cannot contribute. The public inventory still records every
//! conversion and its inventory-only projection remains conservative.
//! Whole-document FBX scaling remains refused.
//!
//! # Quick start
//!
//! ```no_run
//! fn lint_fbx(
//!     path: &std::path::Path,
//! ) -> Result<Vec<animsmith_core::Finding>, Box<dyn std::error::Error>> {
//!     let doc = animsmith_fbx::load(path)?;
//!     let roles = animsmith_core::detect_profile(&doc.skeleton).unwrap_or_default();
//!     let config = animsmith_core::Config::default();
//!     let grids = animsmith_core::MetricGrids::new(&doc);
//!     let ctx = animsmith_core::CheckCtx::new(&grids, &roles, &config);
//!     let results = animsmith_core::evaluate_checks(
//!         &ctx,
//!         &animsmith_core::all_checks(),
//!         animsmith_core::CheckSelection::All,
//!     )?;
//!     Ok(results
//!         .into_iter()
//!         .flat_map(|check| check.findings().to_vec())
//!         .collect())
//! }
//! ```
//!
//! # Build and API status
//!
//! The library crate has no public feature flags and supports the workspace
//! MSRV, Rust 1.88. It includes the bundled `ufbx` C build. Its Rust API is
//! pre-1.0; see `animsmith-core`'s crate-level API status for the shared
//! stability boundary.
//!
//! See the GitHub [embedding guide] for crate selection and the [pipeline
//! scenario guide] for FBX intake and conversion workflows.
//!
//! [embedding guide]: https://github.com/mmannerm/animsmith/blob/main/docs/embedding.md
//! [pipeline scenario guide]: https://github.com/mmannerm/animsmith/blob/main/docs/pipeline-scenarios.md
//!
#![warn(missing_docs)]

mod capability;
mod source_facts;

pub use capability::{
    FbxBindMatrixProvenance, FbxCoordinateAxis, FbxCoordinateNormalization,
    FbxScaleCapabilityInventory, FbxScaleDomainInventory, FbxScaleDomainStatus, FbxScaleSource,
    FbxSourceIdentity, capability_facts, capability_facts_for_source,
    require_clip_track_capability_for_source, rest_bind_capability_facts,
    rest_bind_capability_facts_for_source,
};

use animsmith_core::model::{
    Bone, Clip, Document, Interpolation, MaterialAsset, MeshAsset, MeshInstance,
    NormalTextureAsset, Primitive, Property, SceneAsset, SceneAssets, Skeleton, SourceInfo,
    SourceInverseBindAccessor, SourceInverseBindAccessorStatus, SourceNodeAsset,
    SourceNodeLocalRest, SourceSkeletonAssets, SourceSkeletonCoverage, SourceSkinAsset,
    SourceSkinAttachment, TextureAsset, Track, TrackValues, Transform,
};
use animsmith_core::{
    DependencyClosureBuilderV1, DependencyResourceKeyV1, DependencyResourceRefusalReasonV1,
    DependencyResourceUnavailableReasonV1, InputIdentity, LoadedSource, RawSourceFactsBuilderV1,
    ResourceKeySyntaxV1, SourceFactsError, SourceResourceKindV1, SourceResourceLocatorV1,
    SourceResourceReferenceV1,
};
use capability::AssetConversionFacts;
use glam::{Mat4, Quat, Vec3};
use std::{
    collections::BTreeMap,
    fs::File,
    io::Read,
    path::{Path, PathBuf},
};

/// Independent ceiling for texture bytes retained in normalized assets.
///
/// Dependency identity has its own core-owned capture budgets. This cap
/// prevents multiple material aliases from multiplying retained image bytes.
const FBX_MAX_ASSET_TEXTURE_BYTES: usize = 256 * 1024 * 1024;

/// Errors returned while loading an FBX scene into the core model.
///
/// These errors describe input or parser failures. They do not represent
/// animation check findings; once a [`Document`] loads, semantic problems
/// are reported by `animsmith-core` checks instead.
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum LoadError {
    /// The input path could not be represented as UTF-8 for `ufbx`.
    #[error("path is not valid UTF-8: {0}")]
    Path(String),
    /// `ufbx` rejected or could not parse the file.
    #[error("FBX parse error: {0}")]
    Fbx(String),
    /// `ufbx` loaded the scene but failed while baking an animation take.
    #[error("animation bake failed for take {take:?}: {message}")]
    Bake {
        /// Name of the animation take that failed to bake.
        take: String,
        /// Parser-provided bake failure detail.
        message: String,
    },
    /// The loader produced source facts that violate the core binding contract.
    #[error("invalid FBX source-facts projection: {0}")]
    SourceFacts(#[from] SourceFactsError),
}

fn vec3(v: ufbx::Vec3) -> Vec3 {
    Vec3::new(v.x as f32, v.y as f32, v.z as f32)
}

fn quat(q: ufbx::Quat) -> Quat {
    Quat::from_xyzw(q.x as f32, q.y as f32, q.z as f32, q.w as f32)
}

fn transform(t: &ufbx::Transform) -> Transform {
    Transform {
        translation: vec3(t.translation),
        rotation: quat(t.rotation),
        scale: vec3(t.scale),
    }
}

/// ufbx matrices are 3×4 (rotation/scale columns + translation).
fn mat4(m: &ufbx::Matrix) -> Mat4 {
    Mat4::from_cols_array(&[
        m.m00 as f32,
        m.m10 as f32,
        m.m20 as f32,
        0.0,
        m.m01 as f32,
        m.m11 as f32,
        m.m21 as f32,
        0.0,
        m.m02 as f32,
        m.m12 as f32,
        m.m22 as f32,
        0.0,
        m.m03 as f32,
        m.m13 as f32,
        m.m23 as f32,
        1.0,
    ])
}

/// Project one converted FBX cluster bind only when the complete derivation
/// is finite. `Mat4::inverse()` returns non-finite components for a singular
/// finite input, so checking the two inputs alone is not sufficient evidence.
fn project_cluster_bind(cluster: &ufbx::SkinCluster) -> Option<(Mat4, Mat4)> {
    cluster.bone_node.as_ref()?;
    let bind_to_world = mat4(&cluster.bind_to_world);
    let geometry_to_world = mat4(&cluster.geometry_to_world);
    if !bind_to_world.is_finite() || !geometry_to_world.is_finite() {
        return None;
    }
    let bone_inverse = bind_to_world.inverse();
    let instance_inverse = bone_inverse * geometry_to_world;
    (bone_inverse.is_finite() && instance_inverse.is_finite())
        .then_some((bone_inverse, instance_inverse))
}

/// Load an `.fbx` file into a core [`Document`]: skeleton, animation,
/// and scene assets (triangulated meshes, skins, factor-only
/// materials). Consumers that only judge animation ignore
/// [`Document::assets`].
///
/// # Errors
///
/// Returns [`LoadError::Path`] when the path cannot be passed to `ufbx`,
/// [`LoadError::Fbx`] when the FBX container cannot be parsed, and
/// [`LoadError::Bake`] when an animation stack cannot be baked into the
/// linear TRS tracks that animsmith's checks consume, and
/// [`LoadError::SourceFacts`] when the loader violates a core source-fact
/// binding invariant.
pub fn load(path: &Path) -> Result<Document, LoadError> {
    Ok(load_source(path)?.into_document())
}

/// Load an `.fbx` file and retain bounded importer-sensitive source facts.
///
/// The returned immutable owner binds the normalized document and source facts
/// to the exact primary bytes parsed by ufbx. Consuming it as a document
/// deliberately discards the sidecar.
///
/// # Errors
///
/// Returns [`LoadError::Path`] when the path cannot be passed to `ufbx`,
/// [`LoadError::Fbx`] when the FBX container cannot be parsed,
/// [`LoadError::Bake`] when an animation take cannot be baked, and
/// [`LoadError::SourceFacts`] when the loader violates a core source-fact
/// binding invariant.
pub fn load_source(path: &Path) -> Result<LoadedSource, LoadError> {
    Ok(load_scale_source(path)?.into_source())
}

/// Load an `.fbx` file and retain its conservative scale capability inventory.
///
/// The returned source also owns the shared importer-sensitive source facts;
/// the inventory remains the operation-specific scale view. Neither scale
/// operation is enabled for FBX by this API.
///
/// # Errors
///
/// Returns [`LoadError::Path`] when the path cannot be passed to `ufbx`,
/// [`LoadError::Fbx`] when the FBX container cannot be parsed, and
/// [`LoadError::Bake`] when an animation take cannot be baked, and
/// [`LoadError::SourceFacts`] when the loader violates a core source-fact
/// binding invariant.
pub fn load_scale_source(path: &Path) -> Result<FbxScaleSource, LoadError> {
    path.to_str()
        .ok_or_else(|| LoadError::Path(path.display().to_string()))?;
    let bytes = std::fs::read(path).map_err(|error| LoadError::Fbx(error.to_string()))?;
    let resource_root = path
        .parent()
        .filter(|parent| !parent.as_os_str().is_empty())
        .unwrap_or_else(|| Path::new("."));
    load_scale_source_bytes_with_resource_root(path, &bytes, resource_root)
}

/// Load an FBX byte slice into a core [`Document`].
///
/// `bytes` supplies the top-level container exactly as captured by the
/// caller. This legacy byte-only entry point does not permit external resource
/// I/O; use [`load_bytes_with_resource_root`] when a trusted root is available.
///
/// # Errors
///
/// Returns [`LoadError::Path`] when `path` cannot be passed to `ufbx`,
/// [`LoadError::Fbx`] when the FBX container cannot be parsed, and
/// [`LoadError::Bake`] when an animation stack cannot be baked into the
/// linear TRS tracks that animsmith's checks consume, and
/// [`LoadError::SourceFacts`] when the loader violates a core source-fact
/// binding invariant.
pub fn load_bytes(path: &Path, bytes: &[u8]) -> Result<Document, LoadError> {
    Ok(load_source_bytes(path, bytes)?.into_document())
}

/// Load captured FBX bytes with one explicit trusted resource root.
///
/// External declarations are resolved only below `resource_root`, after
/// lexical normalization and component-by-component symbolic-link refusal.
/// The exact bytes captured here are used both for dependency identity and
/// optional normalized texture assets.
///
/// # Errors
///
/// Returns the same parser and source-facts errors as [`load_bytes`]. Resource
/// failures are represented in the dependency closure rather than as a loader
/// error.
pub fn load_bytes_with_resource_root(
    path: &Path,
    bytes: &[u8],
    resource_root: &Path,
) -> Result<Document, LoadError> {
    Ok(load_source_bytes_with_resource_root(path, bytes, resource_root)?.into_document())
}

/// Load captured FBX bytes and retain bounded importer-sensitive source facts.
///
/// `path` is diagnostics and parser context only. Source identity is computed
/// exclusively from `bytes`; no host path enters the dependency closure. This
/// entry point deliberately performs no external resource I/O.
///
/// # Errors
///
/// Returns [`LoadError::Path`] when `path` cannot be passed to `ufbx`,
/// [`LoadError::Fbx`] when the FBX container cannot be parsed,
/// [`LoadError::Bake`] when an animation take cannot be baked, and
/// [`LoadError::SourceFacts`] when the loader violates a core source-fact
/// binding invariant.
pub fn load_source_bytes(path: &Path, bytes: &[u8]) -> Result<LoadedSource, LoadError> {
    Ok(load_scale_source_bytes_inner(path, bytes, None)?.into_source())
}

/// Load captured FBX bytes and retain source facts plus a rooted dependency
/// closure.
///
/// `resource_root` is the sole filesystem authority for external FBX
/// resources. It is not serialized or included in diagnostics, reports, or
/// dependency identity.
///
/// # Errors
///
/// Returns the same parser and source-facts errors as [`load_source_bytes`].
pub fn load_source_bytes_with_resource_root(
    path: &Path,
    bytes: &[u8],
    resource_root: &Path,
) -> Result<LoadedSource, LoadError> {
    Ok(load_scale_source_bytes_inner(path, bytes, Some(resource_root))?.into_source())
}

/// Load captured FBX bytes and retain the capability inventory from the same parse.
///
/// `path` supplies source provenance and parser context; `bytes` is the exact
/// captured top-level FBX container. This legacy byte-only entry point does
/// not permit external resource I/O; use
/// [`load_scale_source_bytes_with_resource_root`] for rooted capture.
///
/// # Errors
///
/// Returns [`LoadError::Path`] when `path` cannot be passed to `ufbx`,
/// [`LoadError::Fbx`] when the FBX container cannot be parsed, and
/// [`LoadError::Bake`] when an animation take cannot be baked, and
/// [`LoadError::SourceFacts`] when the loader violates a core source-fact
/// binding invariant.
pub fn load_scale_source_bytes(path: &Path, bytes: &[u8]) -> Result<FbxScaleSource, LoadError> {
    load_scale_source_bytes_inner(path, bytes, None)
}

/// Load captured FBX bytes with a trusted external-resource root and retain
/// its scale capability inventory.
///
/// The loader captures an accepted external file at most once by normalized
/// logical key. It never follows a symbolic link or treats ufbx's resolved
/// absolute-path field as a path.
///
/// # Errors
///
/// Returns the same parser and source-facts errors as
/// [`load_scale_source_bytes`].
pub fn load_scale_source_bytes_with_resource_root(
    path: &Path,
    bytes: &[u8],
    resource_root: &Path,
) -> Result<FbxScaleSource, LoadError> {
    load_scale_source_bytes_inner(path, bytes, Some(resource_root))
}

fn load_scale_source_bytes_inner(
    path: &Path,
    bytes: &[u8],
    resource_root: Option<&Path>,
) -> Result<FbxScaleSource, LoadError> {
    let filename = path
        .to_str()
        .ok_or_else(|| LoadError::Path(path.display().to_string()))?;
    let opts = ufbx::LoadOpts {
        target_axes: ufbx::CoordinateAxes::right_handed_y_up(),
        target_unit_meters: 1.0,
        space_conversion: ufbx::SpaceConversion::AdjustTransforms,
        geometry_transform_handling: ufbx::GeometryTransformHandling::HelperNodes,
        // FBX scale-compensation inheritance (Maya-style; ubiquitous in
        // Mixamo rigs, every bone carrying scale 0.01) cannot be
        // represented by plain TRS hierarchies like glTF's — ufbx
        // compensates the transforms (with helper nodes as fallback)
        // so standard composition is correct.
        inherit_mode_handling: ufbx::InheritModeHandling::Compensate,
        generate_missing_normals: true,
        // All external capture is rooted, bounded, and accounted for below.
        // Letting ufbx open resources would create an untracked second reader.
        load_external_files: false,
        ignore_missing_external_files: false,
        filename: filename.into(),
        ..Default::default()
    };
    let scene = ufbx::load_memory(bytes, opts).map_err(|e| LoadError::Fbx(format!("{e:?}")))?;

    // Every node becomes a bone (the ufbx root included — it carries
    // the axis/unit adjustment). scene.nodes is ordered parents-first,
    // matching the skeleton invariant; typed_id indexes scene.nodes
    // directly.
    let mut bones: Vec<Bone> = Vec::with_capacity(scene.nodes.len());
    for node in &scene.nodes {
        let name = if node.element.name.is_empty() {
            if node.is_root {
                "<fbx-root>".to_string()
            } else {
                format!("node{}", node.element.typed_id)
            }
        } else {
            node.element.name.to_string()
        };
        bones.push(Bone {
            name,
            parent: node.parent.as_ref().map(|p| p.element.typed_id as usize),
            rest: transform(&node.local_transform),
            inverse_bind: None,
        });
    }
    for cluster in &scene.skin_clusters {
        if let (Some(bone_node), Some((bone_inverse, _))) =
            (&cluster.bone_node, project_cluster_bind(cluster))
        {
            let id = bone_node.element.typed_id as usize;
            if id < bones.len() {
                // Joint-centric bind inverse in the converted scene
                // space; the mesh-dependent part lives per mesh in
                // `MeshAsset::skin_ibms`.
                bones[id].inverse_bind = Some(bone_inverse);
            }
        }
    }

    let mut clips = Vec::new();
    for (index, stack) in scene.anim_stacks.iter().enumerate() {
        let take = if stack.element.name.is_empty() {
            format!("take{index}")
        } else {
            stack.element.name.to_string()
        };
        let baked = ufbx::bake_anim(
            &scene,
            &stack.anim,
            ufbx::BakeOpts {
                trim_start_time: true,
                ..Default::default()
            },
        )
        .map_err(|e| LoadError::Bake {
            take: take.clone(),
            message: format!("{e:?}"),
        })?;

        let mut tracks = Vec::new();
        let mut duration = 0.0f64;
        for node in &baked.nodes {
            let bone = node.typed_id as usize;
            if !node.translation_keys.is_empty() {
                let times: Vec<f32> = node
                    .translation_keys
                    .iter()
                    .map(|k| k.time as f32)
                    .collect();
                let values: Vec<Vec3> = node
                    .translation_keys
                    .iter()
                    .map(|k| vec3(k.value))
                    .collect();
                duration = duration.max(times.last().copied().unwrap_or(0.0) as f64);
                tracks.push(Track {
                    bone,
                    property: Property::Translation,
                    interpolation: Interpolation::Linear,
                    times,
                    values: TrackValues::Vec3s(values),
                });
            }
            if !node.rotation_keys.is_empty() {
                let times: Vec<f32> = node.rotation_keys.iter().map(|k| k.time as f32).collect();
                let values: Vec<Quat> = node.rotation_keys.iter().map(|k| quat(k.value)).collect();
                duration = duration.max(times.last().copied().unwrap_or(0.0) as f64);
                tracks.push(Track {
                    bone,
                    property: Property::Rotation,
                    interpolation: Interpolation::Linear,
                    times,
                    values: TrackValues::Quats(values),
                });
            }
            if !node.scale_keys.is_empty() {
                let times: Vec<f32> = node.scale_keys.iter().map(|k| k.time as f32).collect();
                let values: Vec<Vec3> = node.scale_keys.iter().map(|k| vec3(k.value)).collect();
                duration = duration.max(times.last().copied().unwrap_or(0.0) as f64);
                tracks.push(Track {
                    bone,
                    property: Property::Scale,
                    interpolation: Interpolation::Linear,
                    times,
                    values: TrackValues::Vec3s(values),
                });
            }
        }
        clips.push(Clip {
            name: take,
            duration_s: duration,
            tracks,
        });
    }

    let construct_counts = source_facts::construct_counts(&scene);
    let raw_facts = source_facts::project(&scene, construct_counts, bytes);
    let (dependency_closure, resource_capture) =
        capture_dependency_closure(&scene, &raw_facts, resource_root)?;
    let (assets, conversion) = extract_assets(&scene, &resource_capture);
    let (inventory, rest_bind_mesh_payload_counts) =
        capability::inventory(&scene, &conversion, construct_counts);

    let document = Document {
        skeleton: Skeleton { bones },
        clips,
        assets,
        source: SourceInfo {
            path: Some(path.display().to_string()),
            format: Some("fbx".into()),
        },
    };
    let source = raw_facts.finish_with_dependency_closure(document, dependency_closure)?;

    Ok(FbxScaleSource {
        source,
        inventory,
        rest_bind_construct_counts: construct_counts.rest_bind,
        rest_bind_scale_invariant_payload_mesh_count: rest_bind_mesh_payload_counts
            .scale_invariant_mesh_count,
    })
}

/// The per-key capture result retained for later aliases without another open.
#[derive(Debug, Clone, Copy)]
enum ExternalCaptureOutcome {
    Captured,
    Refused(DependencyResourceRefusalReasonV1),
    Unavailable(DependencyResourceUnavailableReasonV1),
}

/// Exact external bytes captured once, indexed by normalized logical key.
#[derive(Debug, Default)]
struct FbxResourceCapture {
    outcomes: BTreeMap<DependencyResourceKeyV1, ExternalCaptureOutcome>,
    bytes_by_key: BTreeMap<DependencyResourceKeyV1, Vec<u8>>,
    texture_keys: BTreeMap<u64, DependencyResourceKeyV1>,
}

impl FbxResourceCapture {
    fn record_resource_key(
        &mut self,
        kind: SourceResourceKindV1,
        source_index: u64,
        key: &DependencyResourceKeyV1,
        outcome: ExternalCaptureOutcome,
    ) {
        if kind == SourceResourceKindV1::Texture
            && matches!(outcome, ExternalCaptureOutcome::Captured)
        {
            self.texture_keys.insert(source_index, key.clone());
        }
    }

    fn texture_bytes(&self, source_index: u64) -> Option<&[u8]> {
        self.texture_keys
            .get(&source_index)
            .and_then(|key| self.bytes_by_key.get(key))
            .map(Vec::as_slice)
    }
}

/// The outcome of one rooted file read without retaining host error text.
#[derive(Debug)]
enum RootedCaptureError {
    Refused(DependencyResourceRefusalReasonV1),
    Unavailable(DependencyResourceUnavailableReasonV1),
}

/// Capture the exact dependency closure after the raw resource prefix exists.
fn capture_dependency_closure(
    scene: &ufbx::Scene,
    facts: &RawSourceFactsBuilderV1,
    resource_root: Option<&Path>,
) -> Result<(animsmith_core::DependencyClosureV1, FbxResourceCapture), SourceFactsError> {
    let mut closure = DependencyClosureBuilderV1::new(
        facts.primary_identity().clone(),
        facts.resource_coverage(),
        facts.resource_rows().len(),
    );
    if !scene.audio_clips.is_empty() {
        // Audio clips are an additional resource-bearing domain without a raw
        // reference row. `texture_files`, in contrast, is ufbx's deduplicated
        // view derived from the already-enumerated `textures` list: every file
        // texture carries its `file_index`, and the texture row binds the same
        // logical locator. Do not make that represented alias view unmodeled.
        closure.mark_unmodeled_resource_domain();
    }

    let mut capture = FbxResourceCapture::default();
    for resource in facts.resource_rows() {
        if !capture_reference(resource, resource_root, &mut closure, &mut capture)? {
            break;
        }
    }
    Ok((closure.finish()?, capture))
}

fn capture_reference(
    resource: &SourceResourceReferenceV1,
    resource_root: Option<&Path>,
    closure: &mut DependencyClosureBuilderV1,
    capture: &mut FbxResourceCapture,
) -> Result<bool, SourceFactsError> {
    let order = resource.source_order_index();
    let kind = resource.kind();
    let source_index = resource.source_index();
    match resource.locator() {
        SourceResourceLocatorV1::Embedded | SourceResourceLocatorV1::DataUri => {
            if !closure.begin_reference(0, 0) {
                return Ok(false);
            }
            closure.push_primary(order, kind, source_index)?;
        }
        SourceResourceLocatorV1::Relative(locator) => {
            if !closure.begin_reference(
                locator.as_str().len(),
                DependencyResourceKeyV1::source_component_count(locator),
            ) {
                return Ok(false);
            }
            let key = match DependencyResourceKeyV1::from_relative(
                locator,
                ResourceKeySyntaxV1::ParserRelativePath,
            ) {
                Ok(key) => key,
                Err(animsmith_core::DependencyClosureError::ResourceKeyTooLong { .. }) => {
                    closure.push_refused(
                        order,
                        kind,
                        source_index,
                        DependencyResourceRefusalReasonV1::Oversized,
                    )?;
                    return Ok(true);
                }
                Err(_) => {
                    closure.push_refused(
                        order,
                        kind,
                        source_index,
                        DependencyResourceRefusalReasonV1::Malformed,
                    )?;
                    return Ok(true);
                }
            };
            match closure.prepare_external_key(&key)? {
                None => return Ok(false),
                Some(false) => {
                    let outcome =
                        capture.outcomes.get(&key).copied().ok_or(
                            animsmith_core::DependencyClosureError::ExternalIdentityMissing,
                        )?;
                    match outcome {
                        ExternalCaptureOutcome::Captured => {
                            closure.push_external_alias(order, kind, source_index, key.clone())?;
                        }
                        ExternalCaptureOutcome::Refused(reason) => {
                            closure.push_refused(order, kind, source_index, reason)?;
                        }
                        ExternalCaptureOutcome::Unavailable(reason) => {
                            closure.push_unavailable(
                                order,
                                kind,
                                source_index,
                                Some(key.clone()),
                                reason,
                            )?;
                        }
                    }
                    capture.record_resource_key(kind, source_index, &key, outcome);
                }
                Some(true) => {
                    let outcome = match resource_root {
                        None => ExternalCaptureOutcome::Unavailable(
                            DependencyResourceUnavailableReasonV1::ResourceRootUnavailable,
                        ),
                        Some(root) => {
                            let byte_limit = closure
                                .max_resource_bytes()
                                .min(closure.remaining_external_bytes());
                            // A zero remaining budget still reads at most one
                            // byte. That bounded N+1 witness lets core retain
                            // the current unavailable row and terminally stop
                            // the prefix without a synthetic identity.
                            let read = match checked_rooted_resource_path(root, &key) {
                                Ok(path) => {
                                    // Record exactly at the actual open boundary, after all
                                    // root/component symlink refusals. A refused path is not
                                    // an open attempt.
                                    closure.record_external_open_attempt(&key)?;
                                    read_file_bounded_path(path, byte_limit)
                                }
                                Err(error) => Err(error),
                            };
                            match read {
                                Ok(bytes) => {
                                    let identity = InputIdentity::from_bytes(&bytes);
                                    if !closure.push_captured_external(
                                        order,
                                        kind,
                                        source_index,
                                        key.clone(),
                                        identity,
                                    )? {
                                        return Ok(false);
                                    }
                                    capture.bytes_by_key.insert(key.clone(), bytes);
                                    ExternalCaptureOutcome::Captured
                                }
                                Err(RootedCaptureError::Refused(reason)) => {
                                    closure.push_refused(order, kind, source_index, reason)?;
                                    ExternalCaptureOutcome::Refused(reason)
                                }
                                Err(RootedCaptureError::Unavailable(reason)) => {
                                    closure.push_unavailable(
                                        order,
                                        kind,
                                        source_index,
                                        Some(key.clone()),
                                        reason,
                                    )?;
                                    ExternalCaptureOutcome::Unavailable(reason)
                                }
                            }
                        }
                    };
                    if resource_root.is_none() {
                        closure.push_unavailable(
                            order,
                            kind,
                            source_index,
                            Some(key.clone()),
                            DependencyResourceUnavailableReasonV1::ResourceRootUnavailable,
                        )?;
                    }
                    capture.outcomes.insert(key.clone(), outcome);
                    capture.record_resource_key(kind, source_index, &key, outcome);
                }
            }
        }
        locator => {
            if !closure.begin_reference(0, 0) {
                return Ok(false);
            }
            let reason = match locator {
                SourceResourceLocatorV1::Absolute => DependencyResourceRefusalReasonV1::Absolute,
                SourceResourceLocatorV1::Escaping => DependencyResourceRefusalReasonV1::Escaping,
                SourceResourceLocatorV1::Remote => DependencyResourceRefusalReasonV1::Remote,
                SourceResourceLocatorV1::Malformed => DependencyResourceRefusalReasonV1::Malformed,
                // Redacted oversized strings consume no normalization work;
                // their typed row remains visible instead of stopping capture.
                SourceResourceLocatorV1::Oversized => DependencyResourceRefusalReasonV1::Oversized,
                SourceResourceLocatorV1::Missing => {
                    closure.push_unavailable(
                        order,
                        kind,
                        source_index,
                        None,
                        DependencyResourceUnavailableReasonV1::Missing,
                    )?;
                    return Ok(true);
                }
                SourceResourceLocatorV1::Embedded
                | SourceResourceLocatorV1::DataUri
                | SourceResourceLocatorV1::Relative(_) => unreachable!(),
            };
            closure.push_refused(order, kind, source_index, reason)?;
        }
    }
    Ok(true)
}

/// Validate a safe logical key below one trusted root without following symlinks.
///
/// This protects the intended root at lookup time. Like ordinary portable
/// filesystem APIs, it assumes the root tree is not concurrently replaced
/// between component inspection and open.
fn checked_rooted_resource_path(
    root: &Path,
    key: &DependencyResourceKeyV1,
) -> Result<PathBuf, RootedCaptureError> {
    let root_metadata = std::fs::symlink_metadata(root).map_err(root_metadata_error)?;
    if root_metadata.file_type().is_symlink() {
        return Err(RootedCaptureError::Refused(
            DependencyResourceRefusalReasonV1::Symlink,
        ));
    }
    if !root_metadata.is_dir() {
        return Err(RootedCaptureError::Unavailable(
            DependencyResourceUnavailableReasonV1::Unreadable,
        ));
    }

    let mut path = PathBuf::from(root);
    let component_count = key.as_str().split('/').count();
    for (index, component) in key.as_str().split('/').enumerate() {
        path.push(component);
        let metadata = std::fs::symlink_metadata(&path).map_err(resource_metadata_error)?;
        if metadata.file_type().is_symlink() {
            return Err(RootedCaptureError::Refused(
                DependencyResourceRefusalReasonV1::Symlink,
            ));
        }
        if index + 1 < component_count && !metadata.is_dir() {
            return Err(RootedCaptureError::Unavailable(
                DependencyResourceUnavailableReasonV1::Unreadable,
            ));
        }
        if index + 1 == component_count && !metadata.is_file() {
            // Devices, FIFOs, sockets, and directories are not dependency
            // files. Refuse before File::open() so they cannot block or cause
            // format-loader side effects.
            return Err(RootedCaptureError::Unavailable(
                DependencyResourceUnavailableReasonV1::Unreadable,
            ));
        }
    }
    Ok(path)
}

fn root_metadata_error(error: std::io::Error) -> RootedCaptureError {
    let reason = if error.kind() == std::io::ErrorKind::NotFound {
        DependencyResourceUnavailableReasonV1::ResourceRootUnavailable
    } else {
        DependencyResourceUnavailableReasonV1::Unreadable
    };
    RootedCaptureError::Unavailable(reason)
}

fn resource_metadata_error(error: std::io::Error) -> RootedCaptureError {
    let reason = if error.kind() == std::io::ErrorKind::NotFound {
        DependencyResourceUnavailableReasonV1::Missing
    } else {
        DependencyResourceUnavailableReasonV1::Unreadable
    };
    RootedCaptureError::Unavailable(reason)
}

fn read_file_bounded_path(path: PathBuf, byte_limit: u64) -> Result<Vec<u8>, RootedCaptureError> {
    let mut file = File::open(path).map_err(resource_metadata_error)?;
    let limit = usize::try_from(byte_limit).map_err(|_| {
        RootedCaptureError::Unavailable(
            DependencyResourceUnavailableReasonV1::ResourceBudgetExceeded,
        )
    })?;
    let mut bytes = Vec::new();
    bytes.try_reserve(limit.min(8 * 1024)).map_err(|_| {
        RootedCaptureError::Unavailable(DependencyResourceUnavailableReasonV1::Unreadable)
    })?;
    file.by_ref()
        .take(byte_limit.saturating_add(1))
        .read_to_end(&mut bytes)
        .map_err(|_| {
            RootedCaptureError::Unavailable(DependencyResourceUnavailableReasonV1::Unreadable)
        })?;
    Ok(bytes)
}

#[derive(Debug)]
struct AssetTextureMaterializer {
    remaining: usize,
}

impl Default for AssetTextureMaterializer {
    fn default() -> Self {
        Self {
            remaining: FBX_MAX_ASSET_TEXTURE_BYTES,
        }
    }
}

impl AssetTextureMaterializer {
    fn materialize(&mut self, bytes: &[u8], mime: &'static str) -> Option<TextureAsset> {
        if bytes.len() > self.remaining {
            return None;
        }
        let mut retained = Vec::new();
        retained.try_reserve_exact(bytes.len()).ok()?;
        retained.extend_from_slice(bytes);
        self.remaining -= bytes.len();
        Some(TextureAsset {
            bytes: retained,
            mime: mime.into(),
        })
    }
}

#[cfg(test)]
mod asset_materializer_tests {
    use super::{AssetTextureMaterializer, FBX_MAX_ASSET_TEXTURE_BYTES};
    use std::io::Write;

    #[test]
    fn aliases_cannot_multiply_retained_texture_bytes_past_the_cap() {
        let bytes = [7u8; 4];
        let mut materializer = AssetTextureMaterializer { remaining: 8 };

        assert!(materializer.materialize(&bytes, "image/png").is_some());
        assert!(materializer.materialize(&bytes, "image/png").is_some());
        assert!(materializer.materialize(&bytes, "image/png").is_none());
        assert_eq!(materializer.remaining, 0);
        assert_eq!(
            AssetTextureMaterializer::default().remaining,
            FBX_MAX_ASSET_TEXTURE_BYTES
        );
    }

    #[test]
    fn bounded_reader_returns_the_cap_plus_one_budget_witness() {
        let mut file = tempfile::NamedTempFile::new().expect("temporary resource file");
        file.write_all(&[1, 2, 3]).expect("write resource bytes");
        file.flush().expect("flush resource bytes");

        let bytes = super::read_file_bounded_path(file.path().to_path_buf(), 2)
            .expect("bounded read succeeds");
        assert_eq!(bytes, [1, 2, 3]);
    }
}

/// Materialize one embedded or previously captured texture without re-opening
/// any path. Only PNG/JPEG pass through (glTF's mandated formats).
fn texture_asset(
    texture: &ufbx::Texture,
    capture: &FbxResourceCapture,
    materializer: &mut AssetTextureMaterializer,
) -> Option<TextureAsset> {
    let bytes: &[u8] = if !texture.content.is_empty() {
        texture.content.as_ref()
    } else {
        capture.texture_bytes(u64::from(texture.element.typed_id))?
    };
    let mime = match bytes.get(..3) {
        Some([0x89, b'P', b'N']) => "image/png",
        Some([0xFF, 0xD8, _]) => "image/jpeg",
        _ => return None,
    };
    materializer.materialize(bytes, mime)
}

fn base_color_texture(
    material: &ufbx::Material,
    capture: &FbxResourceCapture,
    materializer: &mut AssetTextureMaterializer,
) -> Option<TextureAsset> {
    let texture = material.pbr.base_color.texture.as_ref().or(material
        .fbx
        .diffuse_color
        .texture
        .as_ref())?;
    texture_asset(texture, capture, materializer)
}

fn normal_texture(
    material: &ufbx::Material,
    capture: &FbxResourceCapture,
    materializer: &mut AssetTextureMaterializer,
) -> Option<NormalTextureAsset> {
    let texture = material.pbr.normal_map.texture.as_ref().or(material
        .fbx
        .normal_map
        .texture
        .as_ref())?;
    texture_asset(texture, capture, materializer).map(|texture| NormalTextureAsset {
        texture,
        // ufbx exposes the linked image but no glTF-compatible normal X/Y
        // scalar for ordinary FBX materials. Preserve the image and use the
        // glTF default rather than guessing from unrelated bump fields.
        scale: 1.0,
    })
}

#[derive(Debug, Clone, Copy, PartialEq)]
enum ProjectedInfluence {
    Absent,
    Retained(u16, f32),
    Rejected,
}

fn project_skin_influence(
    source_weight: f64,
    cluster_index: Option<usize>,
    cluster_count: usize,
    cluster_has_bone: bool,
) -> ProjectedInfluence {
    let weight = source_weight as f32;
    if !source_weight.is_finite()
        || source_weight < 0.0
        || !weight.is_finite()
        || (source_weight > 0.0 && weight == 0.0)
    {
        return ProjectedInfluence::Rejected;
    }
    if weight == 0.0 {
        return ProjectedInfluence::Absent;
    }
    let Some(cluster_index) = cluster_index else {
        return ProjectedInfluence::Rejected;
    };
    if cluster_index >= cluster_count || !cluster_has_bone {
        return ProjectedInfluence::Rejected;
    }
    match u16::try_from(cluster_index) {
        Ok(index) => ProjectedInfluence::Retained(index, weight),
        Err(_) => ProjectedInfluence::Rejected,
    }
}

/// Project every normalized ufbx node and skin deformer in stable typed-list
/// order. These are source-side identities after the documented coordinate,
/// helper-node, and inherit-mode normalization; they are not raw FBX object
/// transforms.
fn extract_source_skeleton(scene: &ufbx::Scene) -> SourceSkeletonAssets {
    let nodes = scene
        .nodes
        .iter()
        .map(|node| {
            let mut source = SourceNodeAsset::new(
                node.element.typed_id as usize,
                SourceNodeLocalRest::Trs {
                    translation: vec3(node.local_transform.translation),
                    rotation: quat(node.local_transform.rotation),
                    scale: vec3(node.local_transform.scale),
                },
            );
            source.name = (!node.element.name.is_empty()).then(|| node.element.name.to_string());
            source.parent_source_node_index = node
                .parent
                .as_ref()
                .map(|parent| parent.element.typed_id as usize);
            source.scene_root_indices = if node.is_root { vec![0] } else { Vec::new() };
            source.bone = Some(node.element.typed_id as usize);
            source
        })
        .collect();

    // A missing cluster bone removes a declared joint slot from the current
    // format-neutral shape: SourceSkinAsset has no optional/invalid joint-row
    // representation. Do not filter that slot and still claim complete source
    // coverage. The capability inventory retains the exact incomplete-cluster
    // count while the generic sidecar fails closed as globally unavailable.
    if scene.skin_clusters.iter().any(|cluster| {
        cluster.bone_node.as_ref().is_none_or(|bone| {
            usize::try_from(bone.element.typed_id)
                .ok()
                .is_none_or(|index| index >= scene.nodes.len())
        })
    }) {
        return SourceSkeletonAssets::default();
    }

    let mut attachments = vec![Vec::new(); scene.skin_deformers.len()];
    for node in &scene.nodes {
        let Some(mesh) = &node.mesh else { continue };
        for skin in &mesh.skin_deformers {
            let Some(for_skin) = attachments.get_mut(skin.element.typed_id as usize) else {
                return SourceSkeletonAssets::default();
            };
            for_skin.push(SourceSkinAttachment {
                source_node_index: node.element.typed_id as usize,
                source_mesh_index: Some(mesh.element.typed_id as usize),
            });
        }
    }

    let skins = scene
        .skin_deformers
        .iter()
        .map(|skin| {
            let source_skin_index = skin.element.typed_id as usize;
            let projected_matrices = skin
                .clusters
                .iter()
                .map(|cluster| project_cluster_bind(cluster).map(|(_, bind)| bind))
                .collect::<Option<Vec<_>>>();
            let (status, matrices) = match (skin.clusters.is_empty(), projected_matrices) {
                (true, _) => (SourceInverseBindAccessorStatus::Absent, Vec::new()),
                (false, Some(matrices)) => (SourceInverseBindAccessorStatus::Available, matrices),
                // Unreadable is declaration-wide because the generic shape
                // cannot retain a hole without shifting later joint slots.
                (false, None) => (SourceInverseBindAccessorStatus::Unreadable, Vec::new()),
            };
            SourceSkinAsset {
                source_skin_index,
                name: (!skin.element.name.is_empty()).then(|| skin.element.name.to_string()),
                // FBX skin deformers do not carry a glTF-style explicit
                // skeleton-root declaration. Do not infer one.
                skeleton_root_source_node_index: None,
                joint_source_node_indices: skin
                    .clusters
                    .iter()
                    .filter_map(|cluster| {
                        cluster
                            .bone_node
                            .as_ref()
                            .map(|node| node.element.typed_id as usize)
                    })
                    .collect(),
                inverse_bind_accessor: SourceInverseBindAccessor {
                    status,
                    declared_count: (!skin.clusters.is_empty()).then_some(skin.clusters.len()),
                    matrices,
                },
                attachments: attachments
                    .get_mut(source_skin_index)
                    .map(std::mem::take)
                    .unwrap_or_default(),
            }
        })
        .collect();

    SourceSkeletonAssets {
        coverage: SourceSkeletonCoverage::Complete,
        nodes,
        skins,
    }
}

/// Extract triangulated geometry, skins, and factor-only materials with
/// optional base-color and normal textures. Corner attributes come straight
/// from ufbx's indexed accessors; skin weights keep the top four influences
/// per source vertex and are renormalized.
fn extract_assets(
    scene: &ufbx::Scene,
    capture: &FbxResourceCapture,
) -> (SceneAssets, AssetConversionFacts) {
    let mut assets = SceneAssets::default();
    let mut conversion = AssetConversionFacts::default();
    let mut materializer = AssetTextureMaterializer::default();
    let mut material_index: std::collections::BTreeMap<u32, usize> =
        std::collections::BTreeMap::new();
    let mut normalized_mesh_index_by_source = std::collections::BTreeMap::<u32, usize>::new();

    for (source_node_index, node) in scene.nodes.iter().enumerate() {
        let Some(mesh) = &node.mesh else { continue };
        let node_id = node.element.typed_id as usize;

        // Materials referenced by this mesh, deduped globally by id.
        let local_materials: Vec<usize> = mesh
            .materials
            .iter()
            .map(|m| {
                *material_index
                    .entry(m.element.element_id)
                    .or_insert_with(|| {
                        let base = if m.pbr.base_color.has_value {
                            m.pbr.base_color.value_vec4
                        } else {
                            m.fbx.diffuse_color.value_vec4
                        };
                        let texture = base_color_texture(m, capture, &mut materializer);
                        let normal_texture = normal_texture(m, capture, &mut materializer);
                        assets.materials.push(MaterialAsset {
                            name: m.element.name.to_string(),
                            // Exporter convention: a texture replaces
                            // the factor (they multiply in glTF).
                            base_color: if texture.is_some() {
                                [1.0, 1.0, 1.0, 1.0]
                            } else {
                                [base.x as f32, base.y as f32, base.z as f32, base.w as f32]
                            },
                            metallic: if m.pbr.metalness.has_value {
                                m.pbr.metalness.value_vec4.x as f32
                            } else {
                                0.0
                            },
                            roughness: if m.pbr.roughness.has_value {
                                m.pbr.roughness.value_vec4.x as f32
                            } else {
                                1.0
                            },
                            base_color_texture: texture,
                            normal_texture,
                            metallic_roughness_texture: None,
                            occlusion_texture: None,
                        });
                        assets.materials.len() - 1
                    })
            })
            .collect();

        // Per-vertex skin influences (top 4, renormalized), cluster
        // order defines the joint list.
        let skin = mesh.skin_deformers.first();
        let skin_joints: Vec<usize> = skin
            .map(|s| {
                s.clusters
                    .iter()
                    .map(|c| {
                        c.bone_node
                            .as_ref()
                            .map(|b| b.element.typed_id as usize)
                            .unwrap_or(0)
                    })
                    .collect()
            })
            .unwrap_or_default();
        // glTF inverse bind per joint: bind-world⁻¹ × geometry-to-world,
        // both already in ufbx's converted (metres, Y-up) space —
        // `geometry_to_bone` is raw source units and NOT suitable.
        let skin_ibms: Vec<glam::Mat4> = skin
            .and_then(|s| {
                s.clusters
                    .iter()
                    .map(|cluster| project_cluster_bind(cluster).map(|(_, bind)| bind))
                    .collect::<Option<Vec<_>>>()
            })
            .unwrap_or_default();
        if let Some(&normalized_mesh_index) =
            normalized_mesh_index_by_source.get(&mesh.element.typed_id)
        {
            assets.instances.push(MeshInstance {
                source_node_index,
                node: node_id,
                mesh: normalized_mesh_index,
                skin_joints,
                skin_ibms,
            });
            continue;
        }
        let vertex_influences: Vec<Option<([u16; 4], [f32; 4])>> = skin
            .map(|s| {
                (0..mesh.num_vertices)
                    .map(|v| {
                        let mut pairs: Vec<(u16, f32)> = Vec::new();
                        if let Some(sv) = s.vertices.get(v) {
                            let begin = sv.weight_begin as usize;
                            let end = begin.saturating_add(sv.num_weights as usize);
                            for sw in s.weights.get(begin..end).unwrap_or_default() {
                                let source_weight = sw.weight;
                                let cluster_index = usize::try_from(sw.cluster_index).ok();
                                let cluster_has_bone = cluster_index
                                    .and_then(|index| s.clusters.get(index))
                                    .is_some_and(|cluster| cluster.bone_node.is_some());
                                match project_skin_influence(
                                    source_weight,
                                    cluster_index,
                                    s.clusters.len(),
                                    cluster_has_bone,
                                ) {
                                    ProjectedInfluence::Absent => {}
                                    ProjectedInfluence::Retained(index, weight) => {
                                        pairs.push((index, weight));
                                    }
                                    ProjectedInfluence::Rejected => {
                                        conversion.rejected_influence_count += 1;
                                    }
                                }
                            }
                        }
                        pairs.sort_by(|a, b| b.1.total_cmp(&a.1));
                        if pairs.len() > 4 {
                            conversion.truncated_influence_vertex_count += 1;
                            conversion.discarded_influence_count += pairs.len() - 4;
                        }
                        pairs.truncate(4);
                        let total: f32 = pairs.iter().map(|p| p.1).sum();
                        if pairs.is_empty() || !total.is_finite() || total <= 0.0 {
                            return None;
                        }
                        let mut joints = [0u16; 4];
                        let mut weights = [0f32; 4];
                        let mut renormalized = false;
                        for (slot, (j, w)) in pairs.into_iter().enumerate() {
                            joints[slot] = j;
                            let normalized = if total > 0.0 { w / total } else { 0.0 };
                            renormalized |= normalized.to_bits() != w.to_bits();
                            weights[slot] = normalized;
                        }
                        if renormalized {
                            conversion.renormalized_influence_vertex_count += 1;
                        }
                        Some((joints, weights))
                    })
                    .collect()
            })
            .unwrap_or_default();

        // One primitive per material slot (unindexed corners).
        let slots = local_materials.len().max(1);
        let mut primitives: Vec<Primitive> = (0..slots)
            .map(|slot| Primitive {
                material: local_materials.get(slot).copied(),
                ..Primitive::default()
            })
            .collect();

        let mut tri_indices = vec![0u32; mesh.max_face_triangles * 3];
        for (face_index, &face) in mesh.faces.iter().enumerate() {
            let slot = mesh
                .face_material
                .get(face_index)
                .map(|&m| m as usize)
                .filter(|&m| m < slots)
                .unwrap_or(0);
            let prim = &mut primitives[slot];
            let tris = mesh.triangulate_face(&mut tri_indices, face) as usize;
            for &corner in &tri_indices[..tris * 3] {
                let corner = corner as usize;
                let p = mesh.vertex_position[corner];
                prim.positions
                    .push(Vec3::new(p.x as f32, p.y as f32, p.z as f32));
                if mesh.vertex_normal.exists {
                    let n = mesh.vertex_normal[corner];
                    prim.normals
                        .push(Vec3::new(n.x as f32, n.y as f32, n.z as f32));
                }
                if mesh.vertex_uv.exists {
                    let uv = mesh.vertex_uv[corner];
                    // glTF's texcoord origin is top-left; FBX's is
                    // bottom-left.
                    prim.uvs.push([uv.x as f32, 1.0 - uv.y as f32]);
                }
                if !vertex_influences.is_empty() {
                    let vertex = mesh.vertex_indices[corner] as usize;
                    let (joints, weights) = vertex_influences
                        .get(vertex)
                        .copied()
                        .flatten()
                        .unwrap_or_else(|| {
                            conversion.missing_skin_influence_corner_count += 1;
                            ([0; 4], [0.0; 4])
                        });
                    prim.joints.push(joints);
                    prim.weights.push(weights);
                }
            }
        }
        primitives.retain(|p| !p.positions.is_empty());
        for prim in &mut primitives {
            conversion.pre_weld_vertex_count += prim.positions.len();
            prim.weld();
            conversion.post_weld_vertex_count += prim.positions.len();
        }
        if primitives.is_empty() {
            continue;
        }
        let normalized_mesh_index = assets.meshes.len();
        let source_mesh_index = mesh.element.typed_id as usize;
        normalized_mesh_index_by_source.insert(mesh.element.typed_id, normalized_mesh_index);
        assets.meshes.push(MeshAsset {
            name: mesh.element.name.to_string(),
            // Retain the stable ufbx mesh identity even when an earlier
            // source definition emitted no normalized primitive. The compact
            // normalized vector index is owned independently by MeshInstance.
            source_mesh_index,
            primitives,
        });
        assets.instances.push(MeshInstance {
            source_node_index,
            node: node_id,
            mesh: normalized_mesh_index,
            skin_joints,
            skin_ibms,
        });
    }
    assets.scenes.push(SceneAsset {
        source_scene_index: 0,
        name: None,
        roots: scene
            .nodes
            .iter()
            .filter(|node| node.is_root)
            .map(|node| node.element.typed_id as usize)
            .collect(),
    });
    assets.default_scene = Some(0);
    assets.source_skeleton = extract_source_skeleton(scene);
    (assets, conversion)
}

#[cfg(test)]
mod tests {
    use super::{ProjectedInfluence, project_skin_influence};

    #[test]
    fn influence_projection_checks_sign_range_and_u16_cluster_narrowing() {
        assert_eq!(
            project_skin_influence(0.0, Some(0), 1, true),
            ProjectedInfluence::Absent
        );
        assert_eq!(
            project_skin_influence(-0.25, Some(0), 1, true),
            ProjectedInfluence::Rejected
        );
        assert_eq!(
            project_skin_influence(1.0, Some(1), 1, true),
            ProjectedInfluence::Rejected,
            "a source cluster index outside the declaration must not survive"
        );
        assert_eq!(
            project_skin_influence(
                1.0,
                Some(usize::from(u16::MAX) + 1),
                usize::from(u16::MAX) + 2,
                true,
            ),
            ProjectedInfluence::Rejected,
            "u32/usize cluster identity must not wrap while narrowing to u16"
        );
        assert_eq!(
            project_skin_influence(0.5, Some(7), 8, true),
            ProjectedInfluence::Retained(7, 0.5)
        );
    }
}