Prepare to fully support swept curves

As far as `SweptCurve` is concerned, this is already the full extent of
support that is required. However, triangulation doesn't fully support
them yet. It would need to also approximate curves, in addition to
approximating surfaces.

experiments/2025-03-18/src/geometry/curve.rs

@@ -1,12 +1,17 @@
 use fj_math::{Line, Point, Transform, Vector};
 
 pub trait CurveGeometry {
+    fn clone_curve_geometry(&self) -> Box<dyn CurveGeometry>;
     fn point_from_local(&self, point: Point<1>) -> Point<3>;
     fn project_point(&self, point: Point<3>) -> Point<1>;
     fn translate(&self, offset: Vector<3>) -> Box<dyn CurveGeometry>;
 }
 
 impl CurveGeometry for Line<3> {
+    fn clone_curve_geometry(&self) -> Box<dyn CurveGeometry> {
+        Box::new(*self)
+    }
+
     fn point_from_local(&self, point: Point<1>) -> Point<3> {
         self.point_from_line_coords(point)
     }

experiments/2025-03-18/src/geometry/swept_curve.rs

@@ -1,16 +1,19 @@
-use fj_math::{Line, Point, Transform, Vector};
+use fj_math::{Line, Point, Vector};
 
 use super::CurveGeometry;
 
 pub struct SweptCurve {
-    pub curve: Line<3>,
+    pub curve: Box<dyn CurveGeometry>,
     pub path: Vector<3>,
 }
 
 impl SweptCurve {
     pub fn plane_from_points([a, b, c]: [Point<3>; 3]) -> Self {
         let (curve, _) = Line::from_points([a, b]);
-        Self { curve, path: c - a }
+        Self {
+            curve: Box::new(curve),
+            path: c - a,
+        }
     }
 
     pub fn v(&self) -> Vector<3> {
@@ -37,14 +40,14 @@ impl SweptCurve {
 
     pub fn flip(&self) -> Self {
         Self {
-            curve: self.curve,
+            curve: self.curve.clone_curve_geometry(),
             path: -self.path,
         }
     }
 
     pub fn translate(&self, offset: impl Into<Vector<3>>) -> Self {
         Self {
-            curve: self.curve.transform(&Transform::translation(offset)),
+            curve: self.curve.translate(offset.into()),
             path: self.path,
         }
     }
@@ -59,7 +62,10 @@ mod tests {
     #[test]
     fn project_point() {
         let plane = SweptCurve {
-            curve: Line::from_origin_and_direction([1., 1., 1.], [1., 0., 0.]),
+            curve: Box::new(Line::from_origin_and_direction(
+                [1., 1., 1.],
+                [1., 0., 0.],
+            )),
             path: Vector::from([0., 1., 0.]),
         };
 

experiments/2025-03-18/src/model.rs

@@ -32,10 +32,10 @@ pub fn model(viewer: &Viewer) -> TriMesh {
 
         let surface = Handle::new(Surface {
             geometry: Box::new(SweptCurve {
-                curve: Line::from_origin_and_direction(
+                curve: Box::new(Line::from_origin_and_direction(
                     [0., 0., 1.],
                     [1., 0., 0.],
-                ),
+                )),
                 path: Vector::from([0., 1., 0.]),
             }),
         });