Fix a bug where clear collisions casting a capsule into a segment are missed.

crates/parry2d/tests/geometry/capsule_segment_toi.rs

@@ -0,0 +1,53 @@
+use parry2d::math::{Pose, Vector};
+use parry2d::query::{self, ShapeCastOptions};
+use parry2d::shape::{Capsule, Segment};
+
+/// A capsule 0.1 units from a steep segment should detect collision when
+/// cast toward it. Uses exact coordinates from a game scenario where
+/// GJK's minkowski_ray_cast incorrectly returns None.
+///
+/// The segment [-672,-240] -> [-624,-336] is a 63.4 steep wall.
+/// The capsule (radius=8, half_height=14) at [-653.39, -245.09] is
+/// 0.1 units from the surface and moving toward it at a velocity of [-200, -325]/frame.
+///
+/// Bug: minkowski_ray_cast reaches a full simplex with min_bound slightly
+/// above eps_tol while ltoi > 0, and returns None despite having found
+/// valid contact.
+#[test]
+fn capsule_segment_steep_slope_toi() {
+    // Segment in local space (centered at entity transform [-648, -288])
+    let segment = Segment::new(Vector::new(-24.0, 48.0), Vector::new(24.0, -48.0));
+    let capsule = Capsule::new_y(14.0, 8.0);
+
+    // Exact game positions
+    let segment_pose = Pose::new(Vector::new(-648.0, -288.0), 0.0);
+    let capsule_pose = Pose::new(Vector::new(-653.3891, -245.08746), 0.0);
+
+    // Per-frame remaining velocity (vel / 60fps)
+    let capsule_vel = Vector::new(-3.3333337, -5.4166675);
+
+    let options = ShapeCastOptions {
+        max_time_of_impact: capsule_vel.length(),
+        ..Default::default()
+    };
+
+    let result = query::cast_shapes(
+        &capsule_pose,
+        capsule_vel,
+        &capsule,
+        &segment_pose,
+        Vector::ZERO,
+        &segment,
+        options,
+    )
+    .unwrap();
+
+    // The capsule is 0.1 units from the segment surface, moving toward it.
+    // The collision should be detected well within the cast distance.
+    assert!(
+        result.is_some(),
+        "GJK missed a collision: capsule is 0.1 units from a steep segment \
+         and moving directly toward it. This is a clear hit that should \
+         never be missed.",
+    );
+}

crates/parry2d/tests/geometry/mod.rs

@@ -1,6 +1,7 @@
 mod aabb_scale;
 mod ball_ball_toi;
 mod ball_cuboid_contact;
+mod capsule_segment_toi;
 mod epa2;
 mod epa_convergence;
 mod ray_cast;

src/query/gjk/gjk.rs

@@ -784,10 +784,14 @@ where
         proj = simplex.project_origin_and_reduce();
 
         if simplex.dimension() == DIM {
-            if min_bound >= _eps_tol {
+            if min_bound >= _eps_tol && ltoi == 0.0 {
+                // Origin is outside the Minkowski difference and the ray
+                // hasn't advanced — genuinely no collision.
                 return None;
             } else {
-                return Some((ltoi / ray_length, ldir)); // Vector inside of the cso.
+                // Either the origin is inside the CSO, or the ray has
+                // advanced (ltoi > 0) meaning contact was found.
+                return Some((ltoi / ray_length, ldir));
             }
         }