Expand and clean up API of Vector

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

@@ -118,7 +118,7 @@ impl Cycle {
                     "Invalid cycle: less than 3 edges, but not all are circles"
                 ),
             };
-            let cross_positive = circle.a().cross(&circle.b()) > Scalar::ZERO;
+            let cross_positive = circle.a().cross2d(&circle.b()) > Scalar::ZERO;
 
             if edge_direction_positive == cross_positive {
                 return Winding::Ccw;

crates/fj-math/src/scalar.rs

@@ -150,6 +150,12 @@ impl Scalar {
     }
 }
 
+impl PartialEq for Scalar {
+    fn eq(&self, other: &Self) -> bool {
+        self.0 == other.0
+    }
+}
+
 impl Eq for Scalar {}
 
 impl PartialOrd for Scalar {
@@ -166,12 +172,6 @@ impl Ord for Scalar {
     }
 }
 
-impl PartialEq for Scalar {
-    fn eq(&self, other: &Self) -> bool {
-        self.0 == other.0
-    }
-}
-
 impl Hash for Scalar {
     fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
         // To the best of my knowledge, this matches the `PartialEq`

crates/fj-math/src/vector.rs

@@ -129,9 +129,15 @@ impl Vector<2> {
     }
 
     /// Compute the 2D cross product with another vector
-    pub fn cross(&self, other: &Self) -> Scalar {
+    pub fn cross2d(&self, other: &Self) -> Scalar {
         (self.u * other.v) - (self.v * other.u)
     }
+
+    /// Determine whether this vector is between two other vectors
+    pub fn is_between(&self, others: [impl Into<Self>; 2]) -> bool {
+        let [a, b] = others.map(Into::into);
+        a.cross2d(self) * b.cross2d(self) < Scalar::ZERO
+    }
 }
 
 impl Vector<3> {
@@ -390,4 +396,13 @@ mod tests {
             Scalar::ZERO
         );
     }
+
+    #[test]
+    fn is_between() {
+        let v = Vector::from([1., 1.]);
+
+        assert!(v.is_between([[1., 0.], [0., 1.]]));
+        assert!(!v.is_between([[1., 0.], [0., -1.]]));
+        assert!(!v.is_between([[-1., 0.], [0., 1.]]));
+    }
 }