Add method to reflect vertex along a plane

Sources/Polygon+CSG.swift

@@ -87,21 +87,7 @@ public extension Polygon {
     /// - Parameter plane: The ``Plane`` against which the vertices are to be reflected.
     /// - Returns: A ``Polygon`` representing the reflected vertices.
     func reflect(along plane: Plane) -> Self {
-        mapVertices {
-            let p = $0.position.project(onto: plane)
-            let d = $0.position - p
-
-            //https://math.stackexchange.com/questions/13261/how-to-get-a-reflection-vector
-            //𝑟=𝑑−2(𝑑⋅𝑛)𝑛
-            let n = plane.normal - 2.0 * plane.normal.dot($0.normal) * $0.normal
-
-            return Vertex(
-                p - d,
-                n,
-                $0.texcoord,
-                $0.color
-            )
-        }.inverted()
+        mapVertices { $0.reflect(along: plane) }.inverted()
     }
 }
 

Sources/Vertex.swift

@@ -214,6 +214,25 @@ public extension Vertex {
         vertex.color = color ?? .white
         return vertex
     }
+
+    /// Reflects the vertex along a plane.
+    /// - Parameter plane: The ``Plane`` against which the vertices are to be reflected.
+    /// - Returns: A ``Vertex`` representing the reflected vertex.
+    func reflect(along plane: Plane) -> Self {
+        let p = position.project(onto: plane)
+        let d = position - p
+
+        // https://math.stackexchange.com/questions/13261/how-to-get-a-reflection-vector
+        // 𝑟=𝑑−2(𝑑⋅𝑛)𝑛
+        let n = plane.normal - 2.0 * plane.normal.dot(normal) * normal
+
+        return Self(
+            p - d,
+            n,
+            texcoord,
+            color
+        )
+    }
 }
 
 extension Vertex {

Tests/MeshTests.swift

@@ -361,23 +361,22 @@ class MeshTests: XCTestCase {
     // MARK: Reflection
 
     func testQuadReflectionAlongPlane() {
-
         let quad = Polygon(unchecked: [
             Vertex(Vector(-0.5, 1.0, 0.5), .unitY, Vector(0.0, 1.0), .black),
             Vertex(Vector(0.5, 1.0, 0.5), .unitY, Vector(1.0, 1.0), .black),
             Vertex(Vector(0.5, 1.0, -0.5), .unitY, Vector(1.0, 0.0), .white),
             Vertex(Vector(-0.5, 1.0, -0.5), .unitY, Vector(0.0, 0.0), .white),
         ])
-        
+
         let expected = Polygon(unchecked: [
             Vertex(Vector(-0.5, -1.0, -0.5), -.unitY, Vector(0.0, 0.0), .white),
             Vertex(Vector(0.5, -1.0, -0.5), -.unitY, Vector(1.0, 0.0), .white),
             Vertex(Vector(0.5, -1.0, 0.5), -.unitY, Vector(1.0, 1.0), .black),
             Vertex(Vector(-0.5, -1.0, 0.5), -.unitY, Vector(0.0, 1.0), .black),
         ])
-        
+
         let reflection = quad.reflect(along: .xz)
-        
+
         XCTAssertEqual(reflection.plane.normal, -.unitY)
         XCTAssertEqual(reflection.vertices, expected.vertices)
     }