feat(boundary): trace exact planar loops

src/app/commands/draw.rs

@@ -676,8 +676,21 @@ impl OpenCADStudio {
 
             "BOUNDARY" => {
                 use crate::modules::draw::draw::hatch::BoundaryCommand;
-                let outlines = self.tabs[i].scene.closed_outlines();
-                let new_cmd = BoundaryCommand::new(outlines);
+                let plane = if self.tabs[i].editing_model_space() {
+                    self.tabs[i].ucs_xform().working_plane()
+                } else {
+                    crate::command::WorkingPlane::default()
+                };
+                let sources = self.tabs[i]
+                    .scene
+                    .boundary_sources_on_plane(plane, 1.0e-6);
+                let selected = self.tabs[i]
+                    .scene
+                    .selected_entities()
+                    .iter()
+                    .map(|(handle, _)| *handle)
+                    .collect();
+                let new_cmd = BoundaryCommand::new(sources, selected, plane);
                 self.command_line.push_info(&new_cmd.prompt());
                 self.tabs[i].active_cmd = Some(Box::new(new_cmd));
             }

src/modules/draw/draw/hatch.rs

@@ -9,12 +9,14 @@
 //   Click a point INSIDE a closed region → boundary auto-detected.
 //   Type "S" to switch to manual vertex-picking mode (HATCH/GRADIENT only).
 
-use crate::command::{CadCommand, CmdResult};
+use crate::command::{CadCommand, CmdResult, WorkingPlane};
 use crate::modules::IconKind;
 use crate::scene::model::hatch_model::{HatchModel, HatchPattern, PatFamily};
 use crate::scene::model::wire_model::WireModel;
 use acadrust::Handle;
-use cadkernel::geom2d::{bounded_faces, Line, Tolerance};
+use cadkernel::geom2d::{
+    bounded_faces, contains, ring_nesting_depths, signed_area, Curve, Line, Tolerance,
+};
 use glam::DVec3;
 use crate::t;
 
@@ -850,16 +852,163 @@ impl CadCommand for GradientCommand {
 // ── BOUNDARY command ───────────────────────────────────────────────────────
 
 pub struct BoundaryCommand {
+    sources: rustc_hash::FxHashMap<Handle, crate::scene::BoundarySource>,
+    active_sources: rustc_hash::FxHashMap<Handle, crate::scene::BoundarySource>,
+    restrict_sources: bool,
     outlines: Vec<Vec<[f64; 2]>>,
+    point_regions: Vec<Vec<Vec<[f64; 2]>>>,
+    selected_objects: Vec<Handle>,
+    mode: BoundaryMode,
+    island_style: BoundaryIslandStyle,
+    gap_tolerance: f64,
+    plane: WorkingPlane,
     missed: bool,
 }
 
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum BoundaryMode {
+    PickInside,
+    SelectObjects,
+    GapTolerance { return_to_selection: bool },
+}
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum BoundaryIslandStyle {
+    Normal,
+    Outer,
+    Ignore,
+}
+
 impl BoundaryCommand {
-    pub fn new(outlines: Vec<Vec<[f64; 2]>>) -> Self {
-        Self {
+    pub fn new(
+        sources: rustc_hash::FxHashMap<Handle, crate::scene::BoundarySource>,
+        selected_objects: Vec<Handle>,
+        plane: WorkingPlane,
+    ) -> Self {
+        let outlines = crate::scene::boundary_faces(&sources, 1.0e-6);
+        let mut command = Self {
+            sources,
+            active_sources: rustc_hash::FxHashMap::default(),
+            restrict_sources: false,
             outlines,
+            point_regions: Vec::new(),
+            selected_objects: Vec::new(),
+            mode: BoundaryMode::PickInside,
+            island_style: BoundaryIslandStyle::Normal,
+            gap_tolerance: 1.0e-6,
+            plane,
             missed: false,
+        };
+        if !selected_objects.is_empty() {
+            command.set_boundary_set(selected_objects);
         }
+        command
+    }
+
+    fn set_boundary_set(&mut self, handles: Vec<Handle>) {
+        let restrict_sources = !handles.is_empty();
+        let selected_sources: rustc_hash::FxHashMap<_, _> = handles
+            .iter()
+            .filter_map(|handle| self.sources.get(handle).cloned().map(|source| (*handle, source)))
+            .collect();
+        self.active_sources = selected_sources;
+        self.restrict_sources = restrict_sources;
+        let sources = if self.restrict_sources {
+            &self.active_sources
+        } else {
+            &self.sources
+        };
+        self.outlines = crate::scene::boundary_faces(sources, self.gap_tolerance);
+        self.missed = !handles.is_empty() && self.outlines.is_empty();
+        self.selected_objects = handles;
+        self.point_regions.clear();
+    }
+
+    fn rebuild_faces(&mut self) {
+        self.set_boundary_set(self.selected_objects.clone());
+    }
+
+    fn region_count(&self) -> usize {
+        self.point_regions.len()
+    }
+
+    fn island_label(&self) -> &'static str {
+        match self.island_style {
+            BoundaryIslandStyle::Normal => "Normal",
+            BoundaryIslandStyle::Outer => "Outer",
+            BoundaryIslandStyle::Ignore => "Ignore",
+        }
+    }
+
+    fn picked_region(&self, point: [f64; 2]) -> Option<Vec<Vec<[f64; 2]>>> {
+        let tolerance = Tolerance::new(self.gap_tolerance);
+        let curves = |outline: &Vec<[f64; 2]>| {
+            outline
+                .iter()
+                .copied()
+                .zip(outline.iter().copied().cycle().skip(1))
+                .take(outline.len())
+                .map(|(start, end)| Curve::Line(Line { start, end }))
+                .collect::<Vec<_>>()
+        };
+        let mut containing: Vec<(usize, f64)> = self
+            .outlines
+            .iter()
+            .enumerate()
+            .filter(|(_, outline)| contains(&curves(outline), point, tolerance))
+            .map(|(index, outline)| (index, signed_area(outline).abs()))
+            .collect();
+        containing.sort_by(|left, right| left.1.total_cmp(&right.1));
+        let outer_index = containing.first()?.0;
+        let outer = &self.outlines[outer_index];
+        let outer_curves = curves(outer);
+        let depths = ring_nesting_depths(&self.outlines);
+        let outer_depth = depths.get(outer_index).copied().unwrap_or(0);
+        let mut rings = vec![outer.clone()];
+        if self.island_style == BoundaryIslandStyle::Ignore {
+            return Some(rings);
+        }
+        for (index, candidate) in self.outlines.iter().enumerate() {
+            let Some(seed) = candidate.first().copied() else {
+                continue;
+            };
+            let candidate_curves = curves(candidate);
+            let candidate_depth = depths.get(index).copied().unwrap_or(0);
+            if index == outer_index
+                || candidate_depth <= outer_depth
+                || !contains(&outer_curves, seed, tolerance)
+                || contains(&candidate_curves, point, tolerance)
+            {
+                continue;
+            }
+            if self.island_style == BoundaryIslandStyle::Outer
+                && candidate_depth != outer_depth + 1
+            {
+                continue;
+            }
+            rings.push(candidate.clone());
+        }
+        Some(rings)
+    }
+
+    fn add_point_region(&mut self, region: Vec<Vec<[f64; 2]>>) {
+        if !self.point_regions.iter().any(|existing| existing == &region) {
+            self.point_regions.push(region);
+        }
+    }
+
+    fn make_entities(&self) -> Vec<acadrust::EntityType> {
+        let sources = if self.restrict_sources {
+            &self.active_sources
+        } else {
+            &self.sources
+        };
+        crate::scene::boundary_polyline_entities(
+            &self.point_regions,
+            self.plane,
+            sources,
+            self.gap_tolerance,
+        )
     }
 }
 
@@ -874,31 +1023,222 @@ impl CadCommand for BoundaryCommand {
         } else {
             String::new()
         };
-        t!("BOUNDARY  Pick internal point:%{miss}", miss = miss).into_owned()
-    }
-
-    fn on_point(&mut self, pt: DVec3) -> CmdResult {
-        let xy = [pt.x, pt.y];
-        match resolve_hatch_rings(&self.outlines, xy) {
-            Some(rings) => {
-                self.missed = false;
-                CmdResult::CommitEntitiesAndExit(crate::scene::boundary_entities(&rings))
+        match self.mode {
+            BoundaryMode::PickInside => {
+                t!("BOUNDARY  Pick internal point:%{miss}", miss = miss).into_owned()
             }
-            None => {
-                self.missed = true;
-                CmdResult::NeedPoint
+            BoundaryMode::SelectObjects => {
+                t!("%{cmd}  Select objects:", cmd = self.name()).into_owned()
             }
+            BoundaryMode::GapTolerance { .. } => format!(
+                "BOUNDARY  {} <{}>:",
+                t!("Tolerance"),
+                self.gap_tolerance
+            ),
         }
     }
 
-    fn on_enter(&mut self) -> CmdResult {
-        CmdResult::Cancel
+    fn options(&self) -> Vec<crate::command::CmdOption> {
+        use crate::command::CmdOption;
+        if matches!(self.mode, BoundaryMode::GapTolerance { .. }) {
+            return Vec::new();
+        }
+        if matches!(self.mode, BoundaryMode::SelectObjects) {
+            return vec![CmdOption::enter(t!("Accept").as_ref())];
+        }
+        let island = format!(
+            "{}: {}",
+            t!("Island detection style"),
+            t!(self.island_label())
+        );
+        let mut options = vec![
+            CmdOption::new(t!("Boundary").as_ref(), "O"),
+            CmdOption::new(&island, "S"),
+            CmdOption::new(t!("Tolerance").as_ref(), "G"),
+        ];
+        if self.region_count() > 0 {
+            options.push(CmdOption::enter("Accept"));
+        }
+        options
     }
+
+    fn on_point(&mut self, pt: DVec3) -> CmdResult {
+        if matches!(self.mode, BoundaryMode::PickInside) {
+            let local = self.plane.to_local(pt);
+            match self.picked_region([local.x, local.y]) {
+                Some(region) => {
+                    self.missed = false;
+                    self.add_point_region(region);
+                }
+                None => self.missed = true,
+            }
+        }
+        CmdResult::NeedPoint
+    }
+
+    fn on_enter(&mut self) -> CmdResult {
+        if let BoundaryMode::GapTolerance { return_to_selection } = self.mode {
+            self.mode = if return_to_selection {
+                BoundaryMode::SelectObjects
+            } else {
+                BoundaryMode::PickInside
+            };
+            return CmdResult::NeedPoint;
+        }
+        if matches!(self.mode, BoundaryMode::SelectObjects) {
+            self.mode = BoundaryMode::PickInside;
+            return CmdResult::NeedPoint;
+        }
+        let entities = self.make_entities();
+        if entities.is_empty() {
+            CmdResult::Cancel
+        } else {
+            CmdResult::CommitEntitiesAndExit(entities)
+        }
+    }
+
     fn on_escape(&mut self) -> CmdResult {
         CmdResult::Cancel
     }
-}
 
+    fn wants_text_input(&self) -> bool {
+        true
+    }
+
+    fn dyn_field(&self) -> crate::command::DynField {
+        if matches!(self.mode, BoundaryMode::GapTolerance { .. }) {
+            crate::command::DynField::Scalar
+        } else {
+            crate::command::DynField::Point
+        }
+    }
+
+    fn dyn_commit_as_text(&self) -> bool {
+        matches!(self.mode, BoundaryMode::GapTolerance { .. })
+    }
+
+    fn on_text_input(&mut self, text: &str) -> Option<CmdResult> {
+        if let BoundaryMode::GapTolerance { return_to_selection } = self.mode {
+            if let Ok(value) = text.trim().parse::<f64>() {
+                if value.is_finite() && value > 0.0 {
+                    self.gap_tolerance = value;
+                    self.rebuild_faces();
+                }
+            }
+            self.mode = if return_to_selection {
+                BoundaryMode::SelectObjects
+            } else {
+                BoundaryMode::PickInside
+            };
+            return Some(CmdResult::NeedPoint);
+        }
+        match text.trim().to_ascii_uppercase().as_str() {
+            "O" | "OBJECT" | "OBJECTS" => {
+                self.mode = BoundaryMode::SelectObjects;
+                self.missed = false;
+            }
+            "I" | "INTERNAL" | "POINTS" => {
+                self.mode = BoundaryMode::PickInside;
+                self.missed = false;
+            }
+            "S" | "ISLAND" | "ISLANDS" => {
+                let style = match self.island_style {
+                    BoundaryIslandStyle::Normal => BoundaryIslandStyle::Outer,
+                    BoundaryIslandStyle::Outer => BoundaryIslandStyle::Ignore,
+                    BoundaryIslandStyle::Ignore => BoundaryIslandStyle::Normal,
+                };
+                self.island_style = style;
+                self.point_regions.clear();
+            }
+            "NORMAL" => {
+                self.island_style = BoundaryIslandStyle::Normal;
+                self.point_regions.clear();
+            }
+            "OUTER" => {
+                self.island_style = BoundaryIslandStyle::Outer;
+                self.point_regions.clear();
+            }
+            "IGNORE" => {
+                self.island_style = BoundaryIslandStyle::Ignore;
+                self.point_regions.clear();
+            }
+            "G" | "GAP" | "TOLERANCE" => {
+                self.mode = BoundaryMode::GapTolerance {
+                    return_to_selection: matches!(self.mode, BoundaryMode::SelectObjects),
+                };
+            }
+            _ => return None,
+        }
+        Some(CmdResult::NeedPoint)
+    }
+
+    fn is_selection_gathering(&self) -> bool {
+        matches!(self.mode, BoundaryMode::SelectObjects)
+    }
+
+    fn selection_forces_add(&self) -> bool {
+        matches!(self.mode, BoundaryMode::SelectObjects)
+    }
+
+    fn on_selection_complete(&mut self, handles: Vec<Handle>) -> CmdResult {
+        if matches!(self.mode, BoundaryMode::SelectObjects) {
+            self.set_boundary_set(handles);
+            CmdResult::NeedPoint
+        } else {
+            CmdResult::Cancel
+        }
+    }
+
+    fn on_undo_step(&mut self) -> Option<CmdResult> {
+        if matches!(self.mode, BoundaryMode::PickInside) {
+            self.point_regions.pop().map(|_| CmdResult::NeedPoint)
+        } else {
+            None
+        }
+    }
+
+    fn on_mouse_move(&mut self, pt: DVec3) -> Option<WireModel> {
+        if !matches!(self.mode, BoundaryMode::PickInside) {
+            return None;
+        }
+        let local = self.plane.to_local(pt);
+        let hovered = self.picked_region([local.x, local.y]);
+        let mut rings: Vec<&Vec<[f64; 2]>> = Vec::new();
+        for ring in self.point_regions.iter().flat_map(|region| region.iter()) {
+            if !rings.iter().any(|existing| *existing == ring) {
+                rings.push(ring);
+            }
+        }
+        if let Some(region) = &hovered {
+            for ring in region {
+                if !rings.iter().any(|existing| *existing == ring) {
+                    rings.push(ring);
+                }
+            }
+        }
+        if rings.is_empty() {
+            return None;
+        }
+        let mut points = Vec::new();
+        for ring in rings {
+            if !points.is_empty() {
+                points.push([f64::NAN; 3]);
+            }
+            for [x, y] in ring {
+                points.push(self.plane.to_world(DVec3::new(*x, *y, 0.0)).to_array());
+            }
+            if let Some([x, y]) = ring.first() {
+                points.push(self.plane.to_world(DVec3::new(*x, *y, 0.0)).to_array());
+            }
+        }
+        Some(WireModel::solid_f64(
+            "boundary_preview".into(),
+            points,
+            WireModel::CYAN,
+            false,
+        ))
+    }
+}
 
 // ── Autocomplete registry ─────────────────────────────────
 inventory::submit!(crate::command::CommandRegistration { names: &["BOUNDARY"] });  // BoundaryCommand

src/scene/boundary.rs

@@ -1,10 +1,18 @@
 use super::*;
 
 use cadkernel::geom2d::{
-    bounded_faces, contains, distance_to, segment_crossing, triangulate, Curve, Line,
-    SegmentCrossing, Tolerance,
+    bounded_faces, contains, distance_to, intersect, segment_crossing, triangulate, Curve, Line,
+    SegmentCrossing, Tolerance, Transform as CurveTransform,
 };
 
+use crate::command::WorkingPlane;
+
+#[derive(Clone)]
+pub struct BoundarySource {
+    pub segments: Vec<Line>,
+    pub curves: Vec<Curve>,
+}
+
 /// How far apart two points may be and still be taken for the same one.
 ///
 /// The boundary search runs on already-tessellated wire geometry, so the
@@ -38,6 +46,73 @@ fn wire_segments(wire: &WireModel) -> Vec<Line> {
     segments
 }
 
+fn wire_segments_on_plane(
+    wire: &WireModel,
+    plane: WorkingPlane,
+    tolerance: f64,
+) -> Vec<Line> {
+    let mut segments = Vec::new();
+    let mut previous: Option<glam::DVec3> = None;
+    for (index, high) in wire.points.iter().copied().enumerate() {
+        if !high.iter().all(|value| value.is_finite()) {
+            previous = None;
+            continue;
+        }
+        let low = wire.points_low.get(index).copied().unwrap_or([0.0; 3]);
+        let world = glam::DVec3::new(
+            high[0] as f64 + low[0] as f64,
+            high[1] as f64 + low[1] as f64,
+            high[2] as f64 + low[2] as f64,
+        );
+        let current = plane.to_local(world);
+        if current.z.abs() > tolerance {
+            previous = None;
+            continue;
+        }
+        if let Some(start) = previous {
+            let length = (current.x - start.x).hypot(current.y - start.y);
+            if length > tolerance {
+                segments.push(Line {
+                    start: [start.x, start.y],
+                    end: [current.x, current.y],
+                });
+            }
+        }
+        previous = Some(current);
+    }
+    segments
+}
+
+fn entity_curves_on_plane(
+    entity: &EntityType,
+    plane: WorkingPlane,
+    tolerance: f64,
+) -> Vec<Curve> {
+    let Some(planar) = crate::entities::curve::entity_curve(entity) else {
+        return Vec::new();
+    };
+    let source = planar.plane;
+    let origin = plane.to_local(glam::DVec3::from_array(source.origin));
+    let x_axis = plane.vector_to_local(glam::DVec3::from_array(source.x_axis));
+    let y_axis = plane.vector_to_local(glam::DVec3::from_array(source.y_axis));
+    if origin.z.abs() > tolerance || x_axis.z.abs() > 1.0e-9 || y_axis.z.abs() > 1.0e-9 {
+        return Vec::new();
+    }
+    let Some(curve) = planar.curve.transformed(&CurveTransform {
+        x_axis: [x_axis.x, x_axis.y].into(),
+        y_axis: [y_axis.x, y_axis.y].into(),
+        origin: [origin.x, origin.y].into(),
+    }) else {
+        return Vec::new();
+    };
+    let segments = curve.segments();
+    if segments.is_empty() {
+        vec![curve]
+    } else {
+        segments
+    }
+}
+
 fn ring_seed(model: &HatchModel, wanted: usize) -> Option<[f64; 2]> {
     let mut ring = Vec::new();
     let mut index = 0usize;
@@ -164,6 +239,175 @@ pub(crate) fn boundary_entities(rings: &[Vec<[f64; 2]>]) -> Vec<acadrust::Entity
         .collect()
 }
 
+fn edge_curve(
+    edge: Line,
+    sources: &rustc_hash::FxHashMap<Handle, BoundarySource>,
+    tolerance: f64,
+) -> Option<Curve> {
+    let edge_length = (edge.end[0] - edge.start[0]).hypot(edge.end[1] - edge.start[1]);
+    let mut best = None;
+    let mut best_overlap = 0.0;
+    for source in sources.values() {
+        for segment in &source.segments {
+            if let SegmentCrossing::Overlap { a, .. } =
+                segment_crossing(edge, *segment, Tolerance::new(tolerance))
+            {
+                let overlap = (a[1] - a[0]).abs() * edge_length;
+                if overlap > best_overlap {
+                    best = Some(source);
+                    best_overlap = overlap;
+                }
+            }
+        }
+    }
+    let candidates: Vec<&Curve> = match best {
+        Some(source) => source.curves.iter().collect(),
+        None => sources
+            .values()
+            .flat_map(|source| source.curves.iter())
+            .filter(|curve| {
+                distance_to(curve, edge.start).min(distance_to(curve, edge.end))
+                    <= tolerance * 4.0
+            })
+            .collect(),
+    };
+    candidates
+        .into_iter()
+        .min_by(|left, right| {
+            let error = |curve: &Curve| {
+                distance_to(curve, edge.start) + distance_to(curve, edge.end)
+            };
+            error(left).total_cmp(&error(right))
+        })
+        .cloned()
+}
+
+fn nearest_crossing(a: &Curve, b: &Curve, point: [f64; 2], tolerance: f64) -> Option<[f64; 2]> {
+    intersect(a, b, Tolerance::new(tolerance))
+        .into_iter()
+        .min_by(|left, right| {
+            let distance = |candidate: [f64; 2]| {
+                (candidate[0] - point[0]).hypot(candidate[1] - point[1])
+            };
+            distance(left.point).total_cmp(&distance(right.point))
+        })
+        .map(|crossing| crossing.point)
+}
+
+fn project_to_curve(curve: &Curve, point: [f64; 2]) -> [f64; 2] {
+    curve.point_at(curve.parameter_at(point))
+}
+
+fn refined_boundary_ring(
+    ring: &[[f64; 2]],
+    sources: &rustc_hash::FxHashMap<Handle, BoundarySource>,
+    tolerance: f64,
+) -> (Vec<[f64; 2]>, Vec<Option<Curve>>) {
+    let count = ring.len();
+    if count < 3 {
+        return (ring.to_vec(), Vec::new());
+    }
+    let edge_curves: Vec<_> = (0..count)
+        .map(|index| {
+            edge_curve(
+                Line {
+                    start: ring[index],
+                    end: ring[(index + 1) % count],
+                },
+                sources,
+                tolerance,
+            )
+        })
+        .collect();
+    let points = (0..count)
+        .map(|index| {
+            let point = ring[index];
+            let incoming = edge_curves[(index + count - 1) % count].as_ref();
+            let outgoing = edge_curves[index].as_ref();
+            match (incoming, outgoing) {
+                (Some(a), Some(b)) if a != b => nearest_crossing(a, b, point, tolerance)
+                    .unwrap_or_else(|| project_to_curve(b, point)),
+                (Some(curve), _) | (_, Some(curve)) => project_to_curve(curve, point),
+                _ => point,
+            }
+        })
+        .collect();
+    (points, edge_curves)
+}
+
+fn normalized_delta(from: f64, to: f64) -> f64 {
+    (to - from + std::f64::consts::PI)
+        .rem_euclid(std::f64::consts::TAU)
+        - std::f64::consts::PI
+}
+
+fn curve_edge_bulge(curve: &Curve, start: [f64; 2], end: [f64; 2]) -> f64 {
+    let direct = match curve {
+        Curve::Circle(circle) => Some((circle.centre, circle.radius)),
+        Curve::Arc(arc) => Some((arc.centre, arc.radius)),
+        _ => None,
+    };
+    if let Some((centre, radius)) = direct {
+        if radius.abs() <= 1.0e-12 {
+            return 0.0;
+        }
+        let start_angle = (start[1] - centre[1]).atan2(start[0] - centre[0]);
+        let end_angle = (end[1] - centre[1]).atan2(end[0] - centre[0]);
+        return (normalized_delta(start_angle, end_angle) * 0.25).tan();
+    }
+    0.0
+}
+
+fn boundary_polyline(
+    ring: &[[f64; 2]],
+    plane: WorkingPlane,
+    sources: &rustc_hash::FxHashMap<Handle, BoundarySource>,
+    tolerance: f64,
+) -> Option<EntityType> {
+    let (points, edge_curves) = refined_boundary_ring(ring, sources, tolerance);
+    if points.len() < 3 {
+        return None;
+    }
+    let mut polyline = acadrust::entities::LwPolyline::new();
+    polyline.is_closed = true;
+    polyline.vertices = points
+        .iter()
+        .enumerate()
+        .map(|(index, point)| {
+            let mut vertex = acadrust::entities::LwVertex::new(acadrust::types::Vector2::new(
+                point[0], point[1],
+            ));
+            vertex.bulge = edge_curves
+                .get(index)
+                .and_then(|curve| curve.as_ref())
+                .map(|curve| {
+                    curve_edge_bulge(curve, *point, points[(index + 1) % points.len()])
+                })
+                .unwrap_or(0.0);
+            vertex
+        })
+        .collect();
+    Some(plane.place_entity(EntityType::LwPolyline(polyline)))
+}
+
+pub(crate) fn boundary_polyline_entities(
+    regions: &[Vec<Vec<[f64; 2]>>],
+    plane: WorkingPlane,
+    sources: &rustc_hash::FxHashMap<Handle, BoundarySource>,
+    tolerance: f64,
+) -> Vec<EntityType> {
+    let mut rings = Vec::new();
+    for ring in regions.iter().flat_map(|region| region.iter()) {
+        if !rings.iter().any(|existing| *existing == ring) {
+            rings.push(ring);
+        }
+    }
+    rings
+        .into_iter()
+        .filter_map(|ring| boundary_polyline(ring, plane, sources, tolerance))
+        .collect()
+}
+
 impl Scene {
     fn associative_boundary_segments(&self, handles: &[Handle]) -> Vec<Line> {
         self.wire_models_for(handles)
@@ -340,4 +584,65 @@ impl Scene {
         }
         sources
     }
+
+    /// Boundary candidates in the active working plane, with exact curves
+    /// where the source entity exposes them.
+    pub fn boundary_sources_on_plane(
+        &self,
+        plane: WorkingPlane,
+        tolerance: f64,
+    ) -> rustc_hash::FxHashMap<Handle, BoundarySource> {
+        let mut sources: rustc_hash::FxHashMap<Handle, BoundarySource> =
+            rustc_hash::FxHashMap::default();
+        let wires = if let Some(viewport) = self.active_viewport {
+            self.model_wires_for_viewport_arc(viewport, 0.0)
+        } else if self.current_layout == "Model" {
+            let camera = self.camera.borrow().clone();
+            self.model_tile_wires_arc(0, &camera, 1.0, 1.0)
+        } else {
+            self.paper_sheet_wires_arc()
+        };
+        for wire in wires.iter() {
+            let Some(handle) = Self::handle_from_wire_name(&wire.name) else {
+                continue;
+            };
+            let segments = wire_segments_on_plane(wire, plane, tolerance);
+            if segments.is_empty() {
+                continue;
+            }
+            sources
+                .entry(handle)
+                .or_insert_with(|| BoundarySource {
+                    segments: Vec::new(),
+                    curves: Vec::new(),
+                })
+                .segments
+                .extend(segments);
+        }
+        for (&handle, source) in &mut sources {
+            source.curves = self
+                .document
+                .get_entity(handle)
+                .map(|entity| entity_curves_on_plane(entity, plane, tolerance))
+                .unwrap_or_default();
+            source.curves.retain(|curve| {
+                source.segments.iter().any(|segment| {
+                    distance_to(curve, segment.start).max(distance_to(curve, segment.end))
+                        <= tolerance * 4.0
+                })
+            });
+        }
+        sources
+    }
+}
+
+pub(crate) fn boundary_faces(
+    sources: &rustc_hash::FxHashMap<Handle, BoundarySource>,
+    tolerance: f64,
+) -> Vec<Vec<[f64; 2]>> {
+    let segments: Vec<_> = sources
+        .values()
+        .flat_map(|source| source.segments.iter().copied())
+        .collect();
+    bounded_faces(&segments, Tolerance::new(tolerance))
 }

src/scene/mod.rs

@@ -33,7 +33,10 @@ mod project;
 mod scene_markers;
 mod selection;
 
-pub(crate) use boundary::{boundary_entities, ring_source_handles};
+pub(crate) use boundary::{
+    boundary_entities, boundary_faces, boundary_polyline_entities, ring_source_handles,
+    BoundarySource,
+};
 
 // Parallel tessellation free functions live in `convert::tess` (alongside the
 // other tessellation code); re-exported here so this root and sibling topic