Make GlobalEdge undirected

crates/fj-kernel/src/algorithms/reverse/edge.rs

@@ -1,4 +1,4 @@
-use crate::objects::{GlobalEdge, HalfEdge};
+use crate::objects::HalfEdge;
 
 use super::Reverse;
 
@@ -12,18 +12,7 @@ impl Reverse for HalfEdge {
         HalfEdge::new(
             self.curve().clone(),
             vertices,
-            self.global_form().clone().reverse(),
+            self.global_form().clone(),
         )
     }
 }
-
-impl Reverse for GlobalEdge {
-    fn reverse(self) -> Self {
-        let vertices = {
-            let &[a, b] = self.vertices();
-            [b, a]
-        };
-
-        GlobalEdge::new(self.curve().clone(), vertices)
-    }
-}

crates/fj-kernel/src/algorithms/sweep/vertex.rs

@@ -53,7 +53,8 @@ impl Sweep for (Vertex, Surface) {
         // With that out of the way, let's start by creating the `GlobalEdge`,
         // as that is the most straight-forward part of this operations, and
         // we're going to need it soon anyway.
-        let edge_global = vertex.global_form().sweep(path, stores);
+        let (edge_global, vertices_global) =
+            vertex.global_form().sweep(path, stores);
 
         // Next, let's compute the surface coordinates of the two vertices of
         // the output `Edge`, as we're going to need these for the rest of this
@@ -87,15 +88,13 @@ impl Sweep for (Vertex, Surface) {
 
         // And now the vertices. Again, nothing wild here.
         let vertices = {
-            let vertices_global = edge_global.vertices();
-
             // Can be cleaned up, once `zip` is stable:
             // https://doc.rust-lang.org/std/primitive.array.html#method.zip
             let [a_surface, b_surface] = points_surface;
             let [a_global, b_global] = vertices_global;
             let vertices_surface =
                 [(a_surface, a_global), (b_surface, b_global)].map(
-                    |(point_surface, &vertex_global)| {
+                    |(point_surface, vertex_global)| {
                         SurfaceVertex::new(
                             point_surface,
                             surface,
@@ -110,7 +109,7 @@ impl Sweep for (Vertex, Surface) {
             let [a_global, b_global] = vertices_global;
             let vertices = [(a_surface, a_global), (b_surface, b_global)];
 
-            vertices.map(|(vertex_surface, &vertex_global)| {
+            vertices.map(|(vertex_surface, vertex_global)| {
                 Vertex::new(
                     [vertex_surface.position().v],
                     curve.clone(),
@@ -127,15 +126,21 @@ impl Sweep for (Vertex, Surface) {
 }
 
 impl Sweep for GlobalVertex {
-    type Swept = GlobalEdge;
+    type Swept = (GlobalEdge, [GlobalVertex; 2]);
 
     fn sweep(self, path: impl Into<Vector<3>>, stores: &Stores) -> Self::Swept {
         let curve = GlobalCurve::new(stores);
 
         let a = self;
         let b = GlobalVertex::from_position(self.position() + path.into());
 
-        GlobalEdge::new(curve, [a, b])
+        let vertices = [a, b];
+        let global_edge = GlobalEdge::new(curve, vertices);
+
+        // The vertices of the returned `GlobalEdge` are in normalized order,
+        // which means the order can't be relied upon by the caller. Return the
+        // ordered vertices in addition.
+        (global_edge, vertices)
     }
 }
 

crates/fj-kernel/src/algorithms/transform/edge.rs

@@ -38,7 +38,7 @@ impl TransformObject for GlobalEdge {
     fn transform(self, transform: &Transform, stores: &Stores) -> Self {
         let curve = self.curve().clone().transform(transform, stores);
         let vertices = self
-            .vertices()
+            .vertices_in_normalized_order()
             .map(|vertex| vertex.transform(transform, stores));
 
         Self::new(curve, vertices)

crates/fj-kernel/src/objects/edge.rs

@@ -52,8 +52,10 @@ impl HalfEdge {
             the half-edge's global form"
         );
         assert_eq!(
-            &vertices.clone().map(|vertex| *vertex.global_form()),
-            global_form.vertices(),
+            &normalize_vertex_order(
+                vertices.clone().map(|vertex| *vertex.global_form())
+            ),
+            global_form.vertices_in_normalized_order(),
             "The global forms of a half-edge's vertices must match the \
             vertices of the half-edge's global form"
         );
@@ -108,6 +110,11 @@ impl fmt::Display for HalfEdge {
 }
 
 /// An edge, defined in global (3D) coordinates
+///
+/// In contract to [`HalfEdge`], `GlobalEdge` is undirected, meaning it has no
+/// defined direction, and its vertices have no defined order. This means it can
+/// be used to determine whether two [`HalfEdge`]s map to the same `GlobalEdge`,
+/// regardless of their direction.
 #[derive(Clone, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
 pub struct GlobalEdge {
     curve: HandleWrapper<GlobalCurve>,
@@ -116,11 +123,16 @@ pub struct GlobalEdge {
 
 impl GlobalEdge {
     /// Create a new instance
+    ///
+    /// The order of `vertices` is irrelevant. Two `GlobalEdge`s with the same
+    /// `curve` and `vertices` will end up being equal, regardless of the order
+    /// of `vertices` here.
     pub fn new(
         curve: impl Into<HandleWrapper<GlobalCurve>>,
         vertices: [GlobalVertex; 2],
     ) -> Self {
         let curve = curve.into();
+        let vertices = normalize_vertex_order(vertices);
         Self { curve, vertices }
     }
 
@@ -135,10 +147,47 @@ impl GlobalEdge {
 
     /// Access the vertices that bound the edge on the curve
     ///
-    /// An edge has either two bounding vertices or none. The latter is possible
-    /// if the edge's curve is continuous (i.e. connects to itself), and defines
-    /// the whole edge.
-    pub fn vertices(&self) -> &[GlobalVertex; 2] {
+    /// As the name indicates, the order of the returned vertices is normalized
+    /// and might not match the order of the vertices that were passed to
+    /// [`GlobalEdge::new`]. You must not rely on the vertices being in any
+    /// specific order.
+    pub fn vertices_in_normalized_order(&self) -> &[GlobalVertex; 2] {
         &self.vertices
     }
 }
+
+fn normalize_vertex_order([a, b]: [GlobalVertex; 2]) -> [GlobalVertex; 2] {
+    if a < b {
+        [a, b]
+    } else {
+        [b, a]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use pretty_assertions::assert_eq;
+
+    use crate::{objects::Surface, partial::HasPartial, stores::Stores};
+
+    use super::HalfEdge;
+
+    #[test]
+    fn global_edge_equality() {
+        let stores = Stores::new();
+
+        let surface = Surface::xy_plane();
+
+        let a = [0., 0.];
+        let b = [1., 0.];
+
+        let a_to_b = HalfEdge::partial()
+            .as_line_segment_from_points(surface, [a, b])
+            .build(&stores);
+        let b_to_a = HalfEdge::partial()
+            .as_line_segment_from_points(surface, [b, a])
+            .build(&stores);
+
+        assert_eq!(a_to_b.global_form(), b_to_a.global_form());
+    }
+}

crates/fj-kernel/src/partial/objects/edge.rs

@@ -254,7 +254,7 @@ impl From<&GlobalEdge> for PartialGlobalEdge {
     fn from(global_edge: &GlobalEdge) -> Self {
         Self {
             curve: Some(global_edge.curve().clone().into()),
-            vertices: Some(*global_edge.vertices()),
+            vertices: Some(*global_edge.vertices_in_normalized_order()),
         }
     }
 }