Clean up edge approximation code

crates/fj-core/src/algorithms/approx/curve.rs

@@ -0,0 +1,171 @@
+//! Curve approximation
+
+use std::collections::BTreeMap;
+
+use fj_math::Point;
+
+use crate::{
+    geometry::{CurveBoundary, GlobalPath, SurfacePath},
+    objects::{Curve, Surface},
+    storage::{Handle, HandleWrapper},
+};
+
+use super::{Approx, ApproxPoint, Tolerance};
+
+impl Approx
+    for (
+        &Handle<Curve>,
+        SurfacePath,
+        &Surface,
+        CurveBoundary<Point<1>>,
+    )
+{
+    type Approximation = CurveApprox;
+    type Cache = CurveApproxCache;
+
+    fn approx_with_cache(
+        self,
+        tolerance: impl Into<Tolerance>,
+        cache: &mut Self::Cache,
+    ) -> Self::Approximation {
+        let (curve, surface_path, surface, boundary) = self;
+
+        match cache.get(curve, boundary) {
+            Some(approx) => approx,
+            None => {
+                let approx =
+                    approx_curve(&surface_path, surface, boundary, tolerance);
+
+                cache.insert(curve.clone(), boundary, approx)
+            }
+        }
+    }
+}
+
+fn approx_curve(
+    path: &SurfacePath,
+    surface: &Surface,
+    boundary: CurveBoundary<Point<1>>,
+    tolerance: impl Into<Tolerance>,
+) -> CurveApprox {
+    // There are different cases of varying complexity. Circles are the hard
+    // part here, as they need to be approximated, while lines don't need to be.
+    //
+    // This will probably all be unified eventually, as `SurfacePath` and
+    // `GlobalPath` grow APIs that are better suited to implementing this code
+    // in a more abstract way.
+    let points = match (path, surface.geometry().u) {
+        (SurfacePath::Circle(_), GlobalPath::Circle(_)) => {
+            todo!(
+                "Approximating a circle on a curved surface not supported yet."
+            )
+        }
+        (SurfacePath::Circle(_), GlobalPath::Line(_)) => {
+            (path, boundary)
+                .approx_with_cache(tolerance, &mut ())
+                .into_iter()
+                .map(|(point_curve, point_surface)| {
+                    // We're throwing away `point_surface` here, which is a bit
+                    // weird, as we're recomputing it later (outside of this
+                    // function).
+                    //
+                    // It should be fine though:
+                    //
+                    // 1. We're throwing this version away, so there's no danger
+                    //    of inconsistency between this and the later version.
+                    // 2. This version should have been computed using the same
+                    //    path and parameters and the later version will be, so
+                    //    they should be the same anyway.
+                    // 3. Not all other cases handled in this function have a
+                    //    surface point available, so it needs to be computed
+                    //    later anyway, in the general case.
+
+                    let point_global = surface
+                        .geometry()
+                        .point_from_surface_coords(point_surface);
+                    (point_curve, point_global)
+                })
+                .collect()
+        }
+        (SurfacePath::Line(line), _) => {
+            let range_u =
+                CurveBoundary::from(boundary.inner.map(|point_curve| {
+                    [path.point_from_path_coords(point_curve).u]
+                }));
+
+            let approx_u = (surface.geometry().u, range_u)
+                .approx_with_cache(tolerance, &mut ());
+
+            let mut points = Vec::new();
+            for (u, _) in approx_u {
+                let t = (u.t - line.origin().u) / line.direction().u;
+                let point_surface = path.point_from_path_coords([t]);
+                let point_global =
+                    surface.geometry().point_from_surface_coords(point_surface);
+                points.push((u, point_global));
+            }
+
+            points
+        }
+    };
+
+    let points = points
+        .into_iter()
+        .map(|(point_curve, point_global)| {
+            ApproxPoint::new(point_curve, point_global)
+        })
+        .collect();
+    CurveApprox { points }
+}
+
+/// Approximation of [`Curve`], within a specific boundary
+#[derive(Clone)]
+pub struct CurveApprox {
+    /// The points that approximate the curve within the boundary
+    pub points: Vec<ApproxPoint<1>>,
+}
+
+impl CurveApprox {
+    fn reverse(mut self) -> Self {
+        self.points.reverse();
+        self
+    }
+}
+
+/// Cache for curve approximations
+#[derive(Default)]
+pub struct CurveApproxCache {
+    inner:
+        BTreeMap<(HandleWrapper<Curve>, CurveBoundary<Point<1>>), CurveApprox>,
+}
+
+impl CurveApproxCache {
+    fn get(
+        &self,
+        handle: &Handle<Curve>,
+        boundary: CurveBoundary<Point<1>>,
+    ) -> Option<CurveApprox> {
+        let handle = HandleWrapper::from(handle.clone());
+
+        if let Some(approx) = self.inner.get(&(handle.clone(), boundary)) {
+            return Some(approx.clone());
+        }
+        if let Some(approx) = self.inner.get(&(handle, boundary.reverse())) {
+            return Some(approx.clone().reverse());
+        }
+
+        None
+    }
+
+    fn insert(
+        &mut self,
+        handle: Handle<Curve>,
+        boundary: CurveBoundary<Point<1>>,
+        approx: CurveApprox,
+    ) -> CurveApprox {
+        let handle = HandleWrapper::from(handle);
+        self.inner
+            .insert((handle, boundary), approx.clone())
+            .unwrap_or(approx)
+    }
+}

crates/fj-core/src/algorithms/approx/cycle.rs

@@ -9,13 +9,13 @@ use fj_math::Segment;
 use crate::objects::{Cycle, Surface};
 
 use super::{
-    edge::{EdgeApproxCache, HalfEdgeApprox},
+    edge::{HalfEdgeApprox, HalfEdgeApproxCache},
     Approx, ApproxPoint, Tolerance,
 };
 
 impl Approx for (&Cycle, &Surface) {
     type Approximation = CycleApprox;
-    type Cache = EdgeApproxCache;
+    type Cache = HalfEdgeApproxCache;
 
     fn approx_with_cache(
         self,