Fix corner case not being handled

Previously, the algorithm to check, if a line-segment is inside a
polygon did not have a special case for when the start or end of the
segment is on a polygon corner. In case this corner is reflexive,
checking against one line between this corner and an adjacent one may
not be enough.

1 files changed, 35 insertions, 0 deletions

diff --git a/src/math/triangle.rs b/src/math/triangle.rs
index 5cf16e5..35bdcec 100644
--- a/src/math/triangle.rs
+++ b/src/math/triangle.rs
@@ -4,6 +4,7 @@ use nalgebra::{RealField, Scalar};
 use num_traits::Zero;
 
 /// Represents a triangle
+#[derive(Debug)]
 pub struct Triangle<T: Scalar + Copy> {
     /// The three corners of the triangle. Internally, it is made sure that the corners are always
     /// ordered in a counterclockwise manner, to make operations like contains simpler.
@@ -80,6 +81,25 @@ impl<T: Scalar + Copy> Into<[Vec2<T>; 3]> for Triangle<T> {
     }
 }
 
+impl<T: Scalar + Copy + PartialEq> PartialEq for Triangle<T> {
+    fn eq(&self, other: &Self) -> bool {
+        // The indexes of the elements are not important, so try all shifting options.
+        for shift in 0..=2 {
+            if self
+                .corners
+                .iter()
+                .enumerate()
+                .find(|(i, &c)| c != other.corners[(i + shift) % 3])
+                .is_none()
+            {
+                return true;
+            }
+        }
+
+        false
+    }
+}
+
 #[derive(PartialEq, Eq)]
 pub(crate) enum TripletOrientation {
     Clockwise,
@@ -187,6 +207,21 @@ mod test {
     }
 
     #[test]
+    fn equality() {
+        let a = Vec2::new(0., 0.);
+        let b = Vec2::new(-1., -1.);
+        let c = Vec2::new(-2., 0.);
+        let d = Vec2::new(-3., 0.);
+
+        let cmp = Triangle::new(a, b, c);
+
+        assert_eq!(Triangle::new(a, b, c), cmp);
+        assert_eq!(Triangle::new(c, b, a), cmp);
+        assert_eq!(Triangle::new(b, a, c), cmp);
+        assert!(Triangle::new(a, b, d) != cmp);
+    }
+
+    #[test]
     fn triplet_angle() {
         assert_eq!(
             super::triplet_angle(Vec2::new(0., 0.), Vec2::new(0., -1.), Vec2::new(-1., -1.)),