brepkit-operations 3.2.12

//! Face tessellation dispatcher with UV computation.

use brepkit_topology::Topology;
use brepkit_topology::edge::EdgeCurve;
use brepkit_topology::face::{FaceId, FaceSurface};

use super::AnalyticKind;
use super::TriangleMeshUV;
use super::edge_sampling::{plane_axes, segments_for_chord_deviation_a};
use super::nurbs::{
    compute_angular_range, compute_axial_range, compute_sphere_v_range, compute_torus_v_range,
    compute_v_param_range, sphere_analytic_kind, tessellate_nurbs,
};
use super::planar::{tessellate_analytic, tessellate_analytic_with_boundary, tessellate_planar};

/// Diagonal shrink factors for spheres: both u and v are curved
/// simultaneously, so the worst-case chord spans a grid cell's diagonal,
/// whose angular step is `sqrt(2)` times the per-direction step. Sag grows
/// with the square of the step, so the deflection budget must be halved;
/// the angular cap is linear in the step, so it shrinks by `1/sqrt(2)`.
const SPHERE_DIAG_DEFL: f64 = 0.5;
const SPHERE_DIAG_ANG: f64 = std::f64::consts::FRAC_1_SQRT_2;

/// Legacy single shrink factor, kept verbatim for the curvature-floored
/// (mesh-boolean) path so its calibrated tessellations stay bit-identical.
const SPHERE_DIAG_LEGACY: f64 = 0.7;

/// Tessellate a face and return mesh with per-vertex UV coordinates.
///
/// UV coordinates are the parametric (u, v) values of the surface at each
/// vertex. For planar faces, UVs are computed by projecting onto the face
/// plane axes.
///
/// # Errors
///
/// Returns an error if the face geometry cannot be tessellated.
pub fn tessellate_with_uvs(
    topo: &Topology,
    face: FaceId,
    deflection: f64,
) -> Result<TriangleMeshUV, crate::OperationsError> {
    tessellate_with_uvs_a(
        topo,
        face,
        deflection,
        brepkit_math::chord::DEFAULT_ANGULAR_TOL,
    )
}

/// Tessellate a face (with UVs) using explicit linear and angular tolerances.
///
/// # Errors
///
/// Returns an error if the face geometry cannot be tessellated.
pub fn tessellate_with_uvs_a(
    topo: &Topology,
    face: FaceId,
    deflection: f64,
    angular_tol: f64,
) -> Result<TriangleMeshUV, crate::OperationsError> {
    tessellate_with_uvs_floor(topo, face, deflection, angular_tol, false)
}

/// Like [`tessellate_with_uvs_a`] with an explicit curvature-floor selector.
///
/// `curvature_floor` keeps the legacy dense sampling on doubly-curved
/// surfaces; the mesh-boolean path passes `true` (its co-refinement
/// robustness and fallback volume accuracy depend on the density), display
/// and export callers pass `false` (the chord formula already bounds sag).
pub(super) fn tessellate_with_uvs_floor(
    topo: &Topology,
    face: FaceId,
    deflection: f64,
    angular_tol: f64,
    curvature_floor: bool,
) -> Result<TriangleMeshUV, crate::OperationsError> {
    let face_data = topo.face(face)?;
    let is_reversed = face_data.is_reversed();

    let mut result = match face_data.surface() {
        FaceSurface::Plane { normal, .. } => {
            let mesh = tessellate_planar(topo, face_data, *normal, deflection, angular_tol)?;
            let (u_axis, v_axis) = plane_axes(*normal);
            let origin = if mesh.positions.is_empty() {
                brepkit_math::vec::Point3::new(0.0, 0.0, 0.0)
            } else {
                mesh.positions[0]
            };
            let uvs = mesh
                .positions
                .iter()
                .map(|p| {
                    let d: brepkit_math::vec::Vec3 = *p - origin;
                    [d.dot(u_axis), d.dot(v_axis)]
                })
                .collect();
            Ok::<_, crate::OperationsError>(TriangleMeshUV { mesh, uvs })
        }
        FaceSurface::Nurbs(surface) => Ok(tessellate_nurbs(surface, deflection, angular_tol)),
        FaceSurface::Cylinder(cyl) => {
            // Check if the boundary is non-standard (e.g., boolean result
            // with arbitrary polyline boundary instead of circles + seams).
            let has_non_standard_boundary = {
                let wire = topo.wire(face_data.outer_wire())?;
                let mut has_nurbs = false;
                let mut all_line = true;
                for oe in wire.edges() {
                    if let Ok(e) = topo.edge(oe.edge()) {
                        match e.curve() {
                            EdgeCurve::NurbsCurve(_) => has_nurbs = true,
                            EdgeCurve::Line => {}
                            _ => all_line = false,
                        }
                    }
                }
                has_nurbs || (all_line && wire.edges().len() > 4)
            };

            if has_non_standard_boundary {
                tessellate_analytic_with_boundary(topo, face_data, cyl, deflection, angular_tol)
            } else {
                let v_range = compute_axial_range(topo, face_data, cyl.origin(), cyl.axis());
                let u_range = compute_angular_range(topo, face_data, |p| cyl.project_point(p));
                let nu = segments_for_chord_deviation_a(
                    cyl.radius(),
                    u_range.1 - u_range.0,
                    deflection,
                    angular_tol,
                    false,
                );
                let nv = 1;
                let cyl = cyl.clone();
                Ok(tessellate_analytic(
                    |u, v| cyl.evaluate(u, v),
                    |u, v| cyl.normal(u, v),
                    u_range,
                    v_range,
                    nu,
                    nv,
                    AnalyticKind::General,
                ))
            }
        }
        FaceSurface::Cone(cone) => {
            // Boolean results can bound a cone by a winding chain of marched
            // NURBS pieces; the plain analytic sweep below ignores the
            // boundary and skins the full parametric band, so classify
            // meshes lose the wall lobes. Try the locally sampled cycle-rim
            // band first; it declines anything that is not a two-rim band.
            let has_nurbs_boundary = {
                let wire = topo.wire(face_data.outer_wire())?;
                wire.edges().iter().any(|oe| {
                    topo.edge(oe.edge())
                        .is_ok_and(|e| matches!(e.curve(), EdgeCurve::NurbsCurve(_)))
                })
            };
            if has_nurbs_boundary
                && let Some(band) = super::nonplanar::tessellate_band_face_local(
                    topo,
                    face_data,
                    deflection,
                    angular_tol,
                )?
            {
                Ok(band)
            } else {
                let v_range = compute_v_param_range(topo, face_data, |p| cone.project_point(p).1);
                let u_range = compute_angular_range(topo, face_data, |p| cone.project_point(p));
                let max_radius = cone.radius_at(v_range.1.abs().max(v_range.0.abs()));
                let nu = segments_for_chord_deviation_a(
                    max_radius.max(0.01),
                    u_range.1 - u_range.0,
                    deflection,
                    angular_tol,
                    false,
                );
                let nv = 1;
                let kind = if v_range.0.abs() < 1e-10 {
                    AnalyticKind::ConeApex
                } else {
                    AnalyticKind::General
                };
                let cone = cone.clone();
                Ok(tessellate_analytic(
                    |u, v| cone.evaluate(u, v),
                    |u, v| cone.normal(u, v),
                    u_range,
                    v_range,
                    nu,
                    nv,
                    kind,
                ))
            }
        }
        FaceSurface::Sphere(sphere) => {
            let u_range = compute_angular_range(topo, face_data, |p| sphere.project_point(p));
            let v_range = compute_sphere_v_range(topo, face_data, sphere);
            // Both directions are curved at once; the worst-case sag is along
            // the diagonal, so shrink the step to keep it within tol.
            // Without the curvature floor: every normal-section curvature of a
            // sphere is exactly 1/r, and latitude chords are shorter than
            // great-circle chords at the same angular step, so the diag-shrunk
            // chord formula already bounds the surface sag in both directions.
            let (defl_shrink, ang_shrink) = if curvature_floor {
                (SPHERE_DIAG_LEGACY, SPHERE_DIAG_LEGACY)
            } else {
                (SPHERE_DIAG_DEFL, SPHERE_DIAG_ANG)
            };
            let nu = segments_for_chord_deviation_a(
                sphere.radius(),
                u_range.1 - u_range.0,
                deflection * defl_shrink,
                angular_tol * ang_shrink,
                curvature_floor,
            );
            let nv = segments_for_chord_deviation_a(
                sphere.radius(),
                v_range.1 - v_range.0,
                deflection * defl_shrink,
                angular_tol * ang_shrink,
                curvature_floor,
            );
            let kind = sphere_analytic_kind(v_range);
            let sphere = sphere.clone();
            Ok(tessellate_analytic(
                |u, v| sphere.evaluate(u, v),
                |u, v| sphere.normal(u, v),
                u_range,
                v_range,
                nu,
                nv,
                kind,
            ))
        }
        FaceSurface::Torus(torus) => {
            let u_range = compute_angular_range(topo, face_data, |p| torus.project_point(p));
            let v_range = compute_torus_v_range(topo, face_data, torus);
            let nu = segments_for_chord_deviation_a(
                torus.major_radius(),
                u_range.1 - u_range.0,
                deflection,
                angular_tol,
                true,
            );
            let nv = segments_for_chord_deviation_a(
                torus.minor_radius(),
                v_range.1 - v_range.0,
                deflection,
                angular_tol,
                true,
            );
            let torus = torus.clone();
            Ok(tessellate_analytic(
                |u, v| torus.evaluate(u, v),
                |u, v| torus.normal(u, v),
                u_range,
                v_range,
                nu,
                nv,
                AnalyticKind::General,
            ))
        }
    }?;

    if is_reversed {
        for n in &mut result.mesh.normals {
            *n = -*n;
        }
        let tri_count = result.mesh.indices.len() / 3;
        for t in 0..tri_count {
            result.mesh.indices.swap(t * 3 + 1, t * 3 + 2);
        }
    }

    Ok(result)
}