From b828de0aebd09e5226869abf6ec848881dc45bb1 Mon Sep 17 00:00:00 2001
From: Jonathan Cornaz <jonathan.cornaz@gmail.com>
Date: Wed, 23 Aug 2023 20:51:00 +0200
Subject: [PATCH] v3: return normal for ray cast

---
 src/v3/mod.rs             | 14 +++++++++++++-
 src/v3/vector.rs          | 10 ++++++++++
 tests/v3_ray_cast_spec.rs | 22 ++++++++++++++++++++--
 3 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/src/v3/mod.rs b/src/v3/mod.rs
index 615065d..3fb5ea2 100644
--- a/src/v3/mod.rs
+++ b/src/v3/mod.rs
@@ -64,19 +64,30 @@ where
     fn cast(&self, vector: Vec2, target: &B) -> Option<CastHit> {
         let mut max_t1 = f32::MIN;
         let mut min_t2 = f32::MAX;
+        let mut normal = Vec2::ZERO;
         for axis in sat_axes(self, target) {
             let Some((t1, t2)) = cast_projection(
                 self.project_on(axis),
                 vector.dot(axis),
                 target.project_on(axis),
             ) else { return None };
+            if t1 > max_t1 {
+                max_t1 = t1;
+                normal = axis;
+            }
             max_t1 = max_t1.max(t1);
             min_t2 = min_t2.min(t2);
         }
         if min_t2 < max_t1 || max_t1 > 1.0 || max_t1 <= 0.0 {
             return None;
         }
-        Some(CastHit { time: max_t1 })
+        if normal.dot(vector) > 0.0 {
+            normal = -normal;
+        }
+        Some(CastHit {
+            time: max_t1,
+            normal,
+        })
     }
 }
 
@@ -84,6 +95,7 @@ where
 #[non_exhaustive]
 pub struct CastHit {
     pub time: f32,
+    pub normal: Vec2,
 }
 
 pub fn ray_cast(origin: Point, vector: Vec2, target: &impl Shape) -> Option<CastHit> {
diff --git a/src/v3/vector.rs b/src/v3/vector.rs
index a87d3e9..dd3992f 100644
--- a/src/v3/vector.rs
+++ b/src/v3/vector.rs
@@ -21,6 +21,16 @@ impl Vec2 {
         Self::new(value, value)
     }
 
+    #[must_use]
+    pub fn x(self) -> f32 {
+        self.x
+    }
+
+    #[must_use]
+    pub fn y(self) -> f32 {
+        self.y
+    }
+
     #[must_use]
     pub(super) fn dot(self, other: Self) -> f32 {
         (self.x * other.x) + (self.y * other.y)
diff --git a/tests/v3_ray_cast_spec.rs b/tests/v3_ray_cast_spec.rs
index e993bce..5846093 100644
--- a/tests/v3_ray_cast_spec.rs
+++ b/tests/v3_ray_cast_spec.rs
@@ -9,7 +9,7 @@ use rstest::rstest;
     Vec2::ZERO,
     Vec2::X,
     Aabb::from_size(Vec2::new(2.0, 2.0)).with_center_at(Point::new(1.9, 0.0)),
-    Vec2::new(0.9, 0.0)
+    Vec2::new(0.9, 0.0),
 )]
 #[case(
     Vec2::ZERO,
@@ -59,7 +59,7 @@ use rstest::rstest;
     Aabb::from_size(Vec2::new(2.0, 2.0)).with_center_at(Point::new(0.5, 1.9)),
     Vec2::new(0.9, 0.9),
 )]
-fn should_find_contact_point(
+fn should_find_contact_time(
     #[case] origin: impl Into<Point>,
     #[case] vector: Vec2,
     #[case] target: impl Shape,
@@ -73,6 +73,24 @@ fn should_find_contact_point(
     assert_abs_diff_eq!(point.y(), expected_point.y());
 }
 
+#[rstest]
+#[case(Point::ORIGIN, Vec2::X, Aabb::from_size(Vec2::new(2.0, 2.0)).with_center_at(Point::new(1.9, 0.0)), -Vec2::X)]
+#[case(Point::ORIGIN, -Vec2::X, Aabb::from_size(Vec2::new(2.0, 2.0)).with_center_at(Point::new(-1.9, 0.0)), Vec2::X)]
+#[case(Point::ORIGIN, Vec2::Y, Aabb::from_size(Vec2::new(2.0, 2.0)).with_center_at(Point::new(0.0, 1.9)), -Vec2::Y)]
+#[case(Point::ORIGIN, -Vec2::Y, Aabb::from_size(Vec2::new(2.0, 2.0)).with_center_at(Point::new(0.0, -1.9)), Vec2::Y)]
+#[case(Point::ORIGIN, Vec2::new(1.0, 1.0), Aabb::from_size(Vec2::new(2.0, 2.0)).with_center_at(Point::new(1.9, 0.0)), -Vec2::X)]
+fn should_find_contact_normal(
+    #[case] origin: impl Into<Point>,
+    #[case] vector: Vec2,
+    #[case] target: impl Shape,
+    #[case] expected_normal: Vec2,
+) {
+    let origin = origin.into();
+    let normal = ray_cast(origin, vector, &target).unwrap().normal;
+    assert_abs_diff_eq!(normal.x(), expected_normal.x());
+    assert_abs_diff_eq!(normal.y(), expected_normal.y());
+}
+
 #[rstest]
 #[case(Vec2::ZERO, Vec2::X, Aabb::from_size(Vec2::new(2.0, 2.0)).with_center_at(Point::new(2.1, 0.0)))]
 #[case(Vec2::ZERO, Vec2::X, Aabb::from_size(Vec2::new(2.0, 2.0)).with_center_at(Point::new(-2.1, 0.0)))]