Correct spline property value semantics

Cargo.lock

@@ -72,7 +72,7 @@ checksum = "366ffbaa4442f4684d91e2cd7c5ea7c4ed8add41959a31447066e279e432b618"
 [[package]]
 name = "acadrust"
 version = "0.4.1"
-source = "git+https://github.com/HakanSeven12/cadcodec.git?rev=931c4ab#931c4ab0c590b755e280bed318a35f41c57b139f"
+source = "git+https://github.com/ramox81/cadcodec.git?rev=969940a#969940a0e616507b603f3480d2d2780a6d565961"
 dependencies = [
  "ahash 0.8.12",
  "anyhow",

Cargo.toml

@@ -27,7 +27,7 @@ glam = { version = "0.33", features = ["bytemuck"] }
 rfd = "0.17"
 clap = { version = "4", features = ["derive"] }
 env_logger = "0.11"
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "931c4ab", features = ["serde"] }
+acadrust = { git = "https://github.com/ramox81/cadcodec.git", rev = "969940a", features = ["serde"] }
 cadkernel = { git = "https://github.com/HakanSeven12/cadkernel.git", rev = "ff950ce", features = ["acis", "offset"] }
 dwg-thumbnailer = { path = "crates/dwg-thumbnailer" }
 flate2 = "1"
@@ -56,6 +56,9 @@ windows-sys = { version = "0.61", features = ["Win32_UI_Shell", "Win32_UI_Window
 [target.'cfg(target_os = "linux")'.dependencies]
 ashpd = { version = "0.13.13", default-features = false, features = ["async-io", "wayland"] }
 
+[patch."https://github.com/HakanSeven12/cadcodec.git"]
+acadrust = { git = "https://github.com/ramox81/cadcodec.git", rev = "969940a" }
+
 [patch.crates-io]
 iced_core = { git = "https://github.com/iced-rs/iced.git", rev = "23604ff22ab0aad9e00b9327cb7b8546ed84db39" }
 iced_widget = { git = "https://github.com/iced-rs/iced.git", rev = "23604ff22ab0aad9e00b9327cb7b8546ed84db39" }

crates/ocs_plugin_api/Cargo.toml

@@ -14,7 +14,7 @@ serde = { version = "1", features = ["derive"] }
 # Pulled in only by the `host` feature, which adds the `acadrust`-typed
 # `HostApi` runtime surface. The default crate stays dependency-free so engine
 # crates and external tooling can depend on the manifest/ribbon contract cheaply.
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "931c4ab", optional = true, features = ["serde"] }
+acadrust = { git = "https://github.com/ramox81/cadcodec.git", rev = "969940a", optional = true, features = ["serde"] }
 
 # Runtime IPC and serialization (host feature only).
 interprocess = { version = "2", optional = true }
@@ -37,7 +37,7 @@ serde_json = "1"
 serde = { version = "1", features = ["derive"] }
 cargo-lock = "11"
 # acadrust is scanned at build time to generate the embedded type registry.
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "931c4ab", features = ["serde"] }
+acadrust = { git = "https://github.com/ramox81/cadcodec.git", rev = "969940a", features = ["serde"] }
 
 [dev-dependencies]
 serde_json = "1"

crates/ocs_web_worker/Cargo.toml

@@ -8,7 +8,7 @@ publish = false
 crate-type = ["cdylib"]
 
 [dependencies]
-acadrust = { git = "https://github.com/HakanSeven12/cadcodec.git", rev = "931c4ab", features = ["serde"] }
+acadrust = { git = "https://github.com/ramox81/cadcodec.git", rev = "969940a", features = ["serde"] }
 bincode = "1.3"
 serde = { version = "1", features = ["derive"] }
 console_error_panic_hook = "0.1"

src/entities/common.rs

@@ -524,6 +524,28 @@ pub fn edit_prop(label: &str, field: &'static str, value: f64) -> Property {
     }
 }
 
+/// Editable dimensionless number. Unlike coordinates and distances, vector
+/// components and NURBS weights must stay plain decimal values when the
+/// drawing uses engineering, architectural, or fractional length units.
+pub fn edit_scalar_prop(label: &str, field: &'static str, value: f64) -> Property {
+    let precision = unit_context().luprec.max(0) as usize;
+    let formatted = format!("{:.*}", precision, value);
+    let trimmed = if formatted.contains('.') {
+        formatted.trim_end_matches('0').trim_end_matches('.')
+    } else {
+        formatted.as_str()
+    };
+    Property {
+        label: label.into(),
+        field,
+        value: PropValue::EditText(if trimmed.is_empty() || trimmed == "-0" {
+            "0".to_string()
+        } else {
+            trimmed.to_string()
+        }),
+    }
+}
+
 pub fn ro_prop(label: &str, field: &'static str, value: impl Into<String>) -> Property {
     Property {
         label: label.into(),
@@ -563,8 +585,13 @@ pub fn stepper_prop(
 
 pub fn parse_f64(value: &str) -> Option<f64> {
     let t = value.trim();
-    // Angle rows display via AUNITS (#297) — accept those formats back.
-    t.parse::<f64>().ok().or_else(|| parse_angle_deg(t))
+    // Length rows display via LUNITS and angle rows via AUNITS. Accept both
+    // representations back so a value shown by Properties can always be
+    // committed unchanged.
+    t.parse::<f64>()
+        .ok()
+        .or_else(|| parse_length(t))
+        .or_else(|| parse_angle_deg(t))
 }
 
 /// Parse an angle string the panel displayed via AUNITS back to DEGREES:

src/entities/curve.rs

@@ -294,20 +294,101 @@ pub fn spline_curve(spline: &SplineEnt) -> Option<PlanarCurve> {
         .copied()
         .collect();
     let first = points.first()?;
+    if !spline_is_planar(spline) {
+        return None;
+    }
     let normal = normalized(spline.normal);
     let elevation = Vec3::from(xyz(*first)).dot(Vec3::from(xyz(normal)));
     let plane = ocs_plane(normal, elevation);
 
-    let tolerance = PLANARITY_TOLERANCE * scale_of(&points);
+    let tolerance = spline_point_tolerance(&points);
     if !points.iter().all(|p| plane.contains(xyz(*p), tolerance)) {
         return None;
     }
+    if !spline.fit_points.is_empty() {
+        let plane_normal = Vec3::from(plane.normal()?);
+        for tangent in [spline.begin_tangent, spline.end_tangent] {
+            let tangent = Vec3::from(xyz(tangent));
+            if tangent.length_squared() > 1e-18
+                && tangent.dot(plane_normal).abs()
+                    > PLANARITY_TOLERANCE * tangent.length().max(1.0)
+            {
+                return None;
+            }
+        }
+    }
     Some(PlanarCurve::new(
         plane,
         Curve::Nurbs(spline_to_nurbs_on(spline, &plane)?),
     ))
 }
 
+/// Whether the actual spline definition fits some plane. Fit-point tangents
+/// participate because coplanar points can still define a spatial curve when
+/// an endpoint derivative leaves their plane.
+pub fn spline_is_planar(spline: &SplineEnt) -> bool {
+    let points = if spline.fit_points.is_empty() {
+        &spline.control_points
+    } else {
+        &spline.fit_points
+    };
+    let Some(origin) = points.first().copied() else {
+        return true;
+    };
+    let origin = Vec3::from(xyz(origin));
+    let mut directions: Vec<Vec3> = points
+        .iter()
+        .skip(1)
+        .map(|point| Vec3::from(xyz(*point)) - origin)
+        .collect();
+    if !spline.fit_points.is_empty() {
+        directions.extend(
+            [spline.begin_tangent, spline.end_tangent]
+                .into_iter()
+                .map(|tangent| Vec3::from(xyz(tangent))),
+        );
+    }
+
+    let extent = directions
+        .iter()
+        .map(|direction| direction.length())
+        .fold(1.0, f64::max);
+    let tolerance = PLANARITY_TOLERANCE * extent
+        + f64::EPSILON * scale_of(points) * 64.0;
+    let Some(axis) = directions
+        .iter()
+        .copied()
+        .find(|direction| direction.length() > tolerance)
+    else {
+        return true;
+    };
+    let Some(normal) = directions.iter().find_map(|direction| {
+        let cross = axis.cross(*direction);
+        if cross.length() > tolerance * axis.length().max(1.0) {
+            cross.normalize()
+        } else {
+            None
+        }
+    }) else {
+        return true;
+    };
+    directions
+        .iter()
+        .all(|direction| direction.dot(normal).abs() <= tolerance)
+}
+
+fn spline_point_tolerance(points: &[Vector3]) -> f64 {
+    let Some(origin) = points.first().copied() else {
+        return PLANARITY_TOLERANCE;
+    };
+    let origin = Vec3::from(xyz(origin));
+    let extent = points
+        .iter()
+        .map(|point| (Vec3::from(xyz(*point)) - origin).length())
+        .fold(1.0, f64::max);
+    PLANARITY_TOLERANCE * extent + f64::EPSILON * scale_of(points) * 64.0
+}
+
 /// The entity's curve in world XY coordinates.
 ///
 /// The editing commands — TRIM, EXTEND, FILLET, OFFSET — work in plan view,

src/entities/spline.rs

@@ -5,7 +5,8 @@ use cadkernel::space::NurbsCurve3;
 
 use crate::command::EntityTransform;
 use crate::entities::common::{
-    dropdown_grip, edit_prop as edit, parse_f64, ro_prop as ro, round_grip, square_grip,
+    dropdown_grip, edit_prop as edit, edit_scalar_prop as edit_scalar, parse_f64,
+    ro_prop as ro, round_grip, square_grip,
 };
 use crate::entities::traits::RenderConvertible;
 use crate::scene::convert::acad_to_render::{RenderEntity, RenderObject};
@@ -31,7 +32,8 @@ fn to_render(spl: &Spline) -> RenderEntity {
                 // A fit spline through points in space is not a planar curve,
                 // so the kernel has nothing to say about it and the solve
                 // here remains the only description of its shape.
-                None if spl.flags.closed || spl.flags.periodic => {
+                None if spl.flags.periodic => periodic_fit_spline_polyline(spl),
+                None if spl.flags.closed => {
                     catmull_rom_polyline(&spl.fit_points, true)
                 }
                 None => fit_spline_polyline(spl),
@@ -149,7 +151,9 @@ pub(crate) fn measurement_polyline(spl: &Spline) -> Vec<[f64; 3]> {
         if spl.fit_points.len() < 2 {
             return spl.control_points.iter().map(|p| [p.x, p.y, p.z]).collect();
         }
-        return if spl.flags.closed || spl.flags.periodic {
+        return if spl.flags.periodic {
+            periodic_fit_spline_polyline(spl)
+        } else if spl.flags.closed {
             catmull_rom_polyline(&spl.fit_points, true)
         } else {
             fit_spline_polyline(spl)
@@ -311,6 +315,151 @@ fn fit_spline_polyline(spl: &Spline) -> Vec<[f64; 3]> {
     out
 }
 
+/// Spatial counterpart of the planar periodic interpolator. The cyclic
+/// derivative system gives the seam the same C² continuity as every interior
+/// fit point instead of only drawing a final chord back to the start.
+fn periodic_fit_spline_polyline(spl: &Spline) -> Vec<[f64; 3]> {
+    let mut points: Vec<[f64; 3]> = spl
+        .fit_points
+        .iter()
+        .map(|point| [point.x, point.y, point.z])
+        .collect();
+    if points.len() > 1 {
+        let first = points[0];
+        let last = points[points.len() - 1];
+        let distance2: f64 = (0..3).map(|axis| (last[axis] - first[axis]).powi(2)).sum();
+        if distance2 <= 1e-18 {
+            points.pop();
+        }
+    }
+    let count = points.len();
+    if count < 3 {
+        return catmull_rom_polyline(&spl.fit_points, true);
+    }
+
+    let step = |from: [f64; 3], to: [f64; 3]| {
+        let chord = (0..3)
+            .map(|axis| (to[axis] - from[axis]).powi(2))
+            .sum::<f64>()
+            .sqrt()
+            .max(1e-9);
+        match spl.knot_parameterization {
+            2 => 1.0,
+            1 => chord.sqrt(),
+            _ => chord,
+        }
+    };
+    let spans: Vec<f64> = (0..count)
+        .map(|index| step(points[index], points[(index + 1) % count]))
+        .collect();
+    let mut matrix = vec![vec![0.0; count]; count];
+    let mut right = vec![[0.0; 3]; count];
+    for index in 0..count {
+        let previous = (index + count - 1) % count;
+        let next = (index + 1) % count;
+        let before = spans[previous];
+        let after = spans[index];
+        matrix[index][previous] += after;
+        matrix[index][index] += 2.0 * (before + after);
+        matrix[index][next] += before;
+        for axis in 0..3 {
+            let previous_slope = (points[index][axis] - points[previous][axis]) / before;
+            let next_slope = (points[next][axis] - points[index][axis]) / after;
+            right[index][axis] =
+                3.0 * (after * previous_slope + before * next_slope);
+        }
+    }
+    let Some(slopes) = solve_spatial_system(matrix, right) else {
+        return catmull_rom_polyline(&spl.fit_points, true);
+    };
+
+    let mut out = Vec::new();
+    for index in 0..count {
+        let next = (index + 1) % count;
+        let span = spans[index];
+        let point_at = |u: f64| {
+            let (u2, u3) = (u * u, u * u * u);
+            let basis = [
+                2.0 * u3 - 3.0 * u2 + 1.0,
+                u3 - 2.0 * u2 + u,
+                -2.0 * u3 + 3.0 * u2,
+                u3 - u2,
+            ];
+            let mut point = [0.0; 3];
+            for axis in 0..3 {
+                point[axis] = basis[0] * points[index][axis]
+                    + basis[1] * slopes[index][axis] * span
+                    + basis[2] * points[next][axis]
+                    + basis[3] * slopes[next][axis] * span;
+            }
+            point
+        };
+        let tangent_at = |u: f64| {
+            let u2 = u * u;
+            let basis = [
+                6.0 * u2 - 6.0 * u,
+                3.0 * u2 - 4.0 * u + 1.0,
+                -6.0 * u2 + 6.0 * u,
+                3.0 * u2 - 2.0 * u,
+            ];
+            let mut tangent = [0.0; 3];
+            for axis in 0..3 {
+                tangent[axis] = basis[0] * points[index][axis]
+                    + basis[1] * slopes[index][axis] * span
+                    + basis[2] * points[next][axis]
+                    + basis[3] * slopes[next][axis] * span;
+            }
+            tangent
+        };
+        let sampled = cadkernel::tessellation::sample_curve3_angle(
+            point_at,
+            tangent_at,
+            cadkernel::tessellation::DEFAULT_ANGLE,
+        );
+        out.extend(sampled.into_iter().skip(usize::from(index > 0)));
+    }
+    out
+}
+
+fn solve_spatial_system(
+    mut matrix: Vec<Vec<f64>>,
+    mut right: Vec<[f64; 3]>,
+) -> Option<Vec<[f64; 3]>> {
+    let count = right.len();
+    for column in 0..count {
+        let pivot = (column..count).max_by(|&left, &right_index| {
+            matrix[left][column]
+                .abs()
+                .total_cmp(&matrix[right_index][column].abs())
+        })?;
+        if matrix[pivot][column].abs() < 1e-14 {
+            return None;
+        }
+        matrix.swap(column, pivot);
+        right.swap(column, pivot);
+        for row in column + 1..count {
+            let factor = matrix[row][column] / matrix[column][column];
+            for entry in column..count {
+                matrix[row][entry] -= factor * matrix[column][entry];
+            }
+            for axis in 0..3 {
+                right[row][axis] -= factor * right[column][axis];
+            }
+        }
+    }
+
+    let mut result = vec![[0.0; 3]; count];
+    for row in (0..count).rev() {
+        for axis in 0..3 {
+            let known: f64 = (row + 1..count)
+                .map(|column| matrix[row][column] * result[column][axis])
+                .sum();
+            result[row][axis] = (right[row][axis] - known) / matrix[row][row];
+        }
+    }
+    Some(result)
+}
+
 /// Slopes used by the spatial fit-point interpolator. Keeping this solve
 /// shared lets Properties report the same effective end tangents that the
 /// renderer uses when the stored tangent fields mean "automatic".
@@ -535,49 +684,6 @@ fn convert_to_fit_method(spline: &mut Spline) -> bool {
     true
 }
 
-fn is_planar(spline: &Spline) -> bool {
-    let points = if spline.fit_points.is_empty() {
-        &spline.control_points
-    } else {
-        &spline.fit_points
-    };
-    if points.len() <= 3 {
-        return true;
-    }
-    let origin = points[0];
-    let Some(axis) = points.iter().skip(1).find_map(|point| {
-        let vector = [point.x - origin.x, point.y - origin.y, point.z - origin.z];
-        let length2 = vector.iter().map(|value| value * value).sum::<f64>();
-        (length2 > 1e-18).then_some(vector)
-    }) else {
-        return true;
-    };
-    let Some(normal) = points.iter().skip(1).find_map(|point| {
-        let vector = [point.x - origin.x, point.y - origin.y, point.z - origin.z];
-        let cross = [
-            axis[1] * vector[2] - axis[2] * vector[1],
-            axis[2] * vector[0] - axis[0] * vector[2],
-            axis[0] * vector[1] - axis[1] * vector[0],
-        ];
-        let length2 = cross.iter().map(|value| value * value).sum::<f64>();
-        (length2 > 1e-18).then_some(cross)
-    }) else {
-        return true;
-    };
-    let normal_length = normal.iter().map(|value| value * value).sum::<f64>().sqrt();
-    points.iter().all(|point| {
-        let offset = [point.x - origin.x, point.y - origin.y, point.z - origin.z];
-        let distance = normal
-            .iter()
-            .zip(offset)
-            .map(|(component, value)| component * value)
-            .sum::<f64>()
-            .abs()
-            / normal_length;
-        distance <= 1e-8
-    })
-}
-
 fn tangent_is_set(tangent: &acadrust::types::Vector3) -> bool {
     tangent.x * tangent.x + tangent.y * tangent.y + tangent.z * tangent.z > 1e-18
 }
@@ -753,7 +859,7 @@ fn properties(spline: &Spline) -> Vec<PropSection> {
                 "ctrl_pt_z",
                 point.map(|value| value.z).unwrap_or(0.0),
             ),
-            edit(t!("Weight").as_ref(), "weight", weight),
+            edit_scalar(t!("Weight").as_ref(), "weight", weight),
         ]
     };
     data_points.push(choice_prop(
@@ -785,37 +891,37 @@ fn properties(spline: &Spline) -> Vec<PropSection> {
         ro(
             t!("Planar").as_ref(),
             "planar",
-            yes_no(is_planar(spline)),
+            yes_no(crate::entities::curve::spline_is_planar(spline)),
         ),
     ];
     if fit_method {
         misc.extend([
-            edit(
+            edit_scalar(
                 t!("Start tangent vector X").as_ref(),
                 "start_tan_x",
                 effective_begin_tangent.x,
             ),
-            edit(
+            edit_scalar(
                 t!("Start tangent vector Y").as_ref(),
                 "start_tan_y",
                 effective_begin_tangent.y,
             ),
-            edit(
+            edit_scalar(
                 t!("Start tangent vector Z").as_ref(),
                 "start_tan_z",
                 effective_begin_tangent.z,
             ),
-            edit(
+            edit_scalar(
                 t!("End tangent vector X").as_ref(),
                 "end_tan_x",
                 effective_end_tangent.x,
             ),
-            edit(
+            edit_scalar(
                 t!("End tangent vector Y").as_ref(),
                 "end_tan_y",
                 effective_end_tangent.y,
             ),
-            edit(
+            edit_scalar(
                 t!("End tangent vector Z").as_ref(),
                 "end_tan_z",
                 effective_end_tangent.z,
@@ -855,7 +961,17 @@ fn apply_geom_prop(spline: &mut Spline, field: &str, value: &str) {
                 "Chord" => 0,
                 "Square Root" => 1,
                 "Uniform" => 2,
-                "Custom" => 15,
+                "Custom" => {
+                    // Custom parameterization is an explicit knot/control
+                    // representation, not a fourth automatic spacing rule.
+                    // Materialize the current fit curve before marking it
+                    // custom so rendering and saving cannot silently fall
+                    // back to chord spacing.
+                    if !spline.fit_points.is_empty() && !convert_to_control_method(spline) {
+                        return;
+                    }
+                    15
+                }
                 _ => return,
             };
             return;
@@ -947,7 +1063,7 @@ fn apply_geom_prop(spline: &mut Spline, field: &str, value: &str) {
         }
         _ => {}
     }
-    spline.flags.planar = is_planar(spline);
+    spline.flags.planar = crate::entities::curve::spline_is_planar(spline);
 }
 
 fn apply_grip(spline: &mut Spline, grip_id: usize, apply: GripApply) {
@@ -985,6 +1101,21 @@ fn apply_grip(spline: &mut Spline, grip_id: usize, apply: GripApply) {
 }
 
 fn apply_transform(spline: &mut Spline, t: &EntityTransform) {
+    if let EntityTransform::Mirror {
+        p1,
+        p2,
+        working_normal,
+    } = t
+    {
+        let transform = crate::scene::view::transform::reflection_about_working_line(
+            *p1,
+            *p2,
+            *working_normal,
+        );
+        acadrust::Entity::apply_transform(spline, &transform);
+        spline.flags.planar = crate::entities::curve::spline_is_planar(spline);
+        return;
+    }
     crate::scene::view::transform::apply_standard_entity_transform(spline, t, |entity, p1, p2| {
         for cp in &mut entity.control_points {
             crate::scene::view::transform::reflect_xy_point(&mut cp.x, &mut cp.y, p1, p2);
@@ -993,6 +1124,7 @@ fn apply_transform(spline: &mut Spline, t: &EntityTransform) {
             crate::scene::view::transform::reflect_xy_point(&mut fp.x, &mut fp.y, p1, p2);
         }
     });
+    spline.flags.planar = crate::entities::curve::spline_is_planar(spline);
 }
 
 impl RenderConvertible for Spline {

src/modules/draw/modify/spline_ops.rs

@@ -227,6 +227,91 @@ fn solve_control_points(
     Some(result)
 }
 
+/// A closed C² cubic through every fit point. The cyclic slope solve makes
+/// the first and last derivatives and accelerations agree at the seam; merely
+/// repeating the first point in the open interpolator only closes the shape
+/// and does not make it periodic.
+fn interpolate_periodic(
+    points: &[[f64; 2]],
+    parameterization: Parameterization,
+) -> Option<NurbsCurve> {
+    let mut points = points.to_vec();
+    if points.len() > 1 {
+        let first = points[0];
+        let last = points[points.len() - 1];
+        let dx = last[0] - first[0];
+        let dy = last[1] - first[1];
+        if dx * dx + dy * dy <= 1e-18 {
+            points.pop();
+        }
+    }
+    let count = points.len();
+    if count < 3 {
+        return None;
+    }
+
+    let step = |from: [f64; 2], to: [f64; 2]| {
+        let dx = to[0] - from[0];
+        let dy = to[1] - from[1];
+        let chord = (dx * dx + dy * dy).sqrt().max(1e-9);
+        match parameterization {
+            Parameterization::Uniform => 1.0,
+            Parameterization::Centripetal => chord.sqrt(),
+            Parameterization::Chord => chord,
+        }
+    };
+    let spans: Vec<f64> = (0..count)
+        .map(|index| step(points[index], points[(index + 1) % count]))
+        .collect();
+
+    let mut matrix = vec![vec![0.0; count]; count];
+    let mut right = vec![[0.0; 2]; count];
+    for index in 0..count {
+        let previous = (index + count - 1) % count;
+        let next = (index + 1) % count;
+        let before = spans[previous];
+        let after = spans[index];
+        matrix[index][previous] += after;
+        matrix[index][index] += 2.0 * (before + after);
+        matrix[index][next] += before;
+        for axis in 0..2 {
+            let previous_slope = (points[index][axis] - points[previous][axis]) / before;
+            let next_slope = (points[next][axis] - points[index][axis]) / after;
+            right[index][axis] =
+                3.0 * (after * previous_slope + before * next_slope);
+        }
+    }
+    let slopes = solve_control_points(matrix, right)?;
+
+    let mut controls = Vec::with_capacity(3 * count + 1);
+    let mut boundaries = Vec::with_capacity(count + 1);
+    controls.push(points[0]);
+    boundaries.push(0.0);
+    let mut parameter = 0.0;
+    for index in 0..count {
+        let next = (index + 1) % count;
+        let span = spans[index];
+        controls.push([
+            points[index][0] + slopes[index][0] * span / 3.0,
+            points[index][1] + slopes[index][1] * span / 3.0,
+        ]);
+        controls.push([
+            points[next][0] - slopes[next][0] * span / 3.0,
+            points[next][1] - slopes[next][1] * span / 3.0,
+        ]);
+        controls.push(points[next]);
+        parameter += span;
+        boundaries.push(parameter);
+    }
+
+    let mut knots = vec![0.0; 4];
+    for boundary in boundaries.iter().take(count).skip(1) {
+        knots.extend([*boundary; 3]);
+    }
+    knots.extend([parameter; 4]);
+    NurbsCurve::new(3, controls, knots, None)
+}
+
 /// [`spline_to_nurbs`] with the points expressed in `plane`'s coordinates.
 ///
 /// The two differ only for a spline whose extrusion normal is not +Z. Where
@@ -259,7 +344,15 @@ fn spline_to_nurbs_with(
 
     // No usable control polygon, so this is a fit-point spline.
     let mut fit: Vec<[f64; 2]> = spl.fit_points.iter().map(&point).collect();
-    if spl.flags.closed || spl.flags.periodic {
+    let parameterization = match spl.knot_parameterization {
+        2 => Parameterization::Uniform,
+        1 => Parameterization::Centripetal,
+        _ => Parameterization::Chord,
+    };
+    if spl.flags.periodic {
+        return interpolate_periodic(&fit, parameterization);
+    }
+    if spl.flags.closed {
         // The interpolation is a clamped solve and does not model a wrap, so
         // a closed spline came back as an open curve that never returned to
         // its start — and a TRIM against it then cut nothing along the seam.
@@ -278,11 +371,6 @@ fn spline_to_nurbs_with(
     };
     let start_tangent = tangent(&spl.begin_tangent);
     let end_tangent = tangent(&spl.end_tangent);
-    let parameterization = match spl.knot_parameterization {
-        2 => Parameterization::Uniform,
-        1 => Parameterization::Centripetal,
-        _ => Parameterization::Chord,
-    };
     if !spl.flags.closed && !spl.flags.periodic && spl.fit_tolerance > 0.0 {
         fit = fit_within_tolerance(
             fit,