implement feature_normal_at_point for trimesh (#181)

* implement `feature_normal_at_point` for trimesh

---------

Co-authored-by: Thierry Berger <[email protected]>

CHANGELOG.md

@@ -2,12 +2,16 @@
 
 ## Unreleased
 
+### Added
+
+- `TriMesh` now implements `Shape::feature_normal_at_point` to retrieve the normal of a face, when passing a `FeatureId::Face`.
+
 ## v0.17.1
 
 ### Modified
 
 - Improve convergence of epa algorithm in degenerate configurations.
-- Fix bug in the esh/mesh intersection algorithm that didn’t properly take mesh transforms into account.
+- Fix bug in the mesh/mesh intersection algorithm that didn’t properly take mesh transforms into account.
 
 ## v0.17.0
 

src/shape/shape.rs

@@ -1130,6 +1130,18 @@ impl Shape for TriMesh {
         Real::frac_pi_4()
     }
 
+    /// Gets the normal of the triangle represented by `feature`.
+    fn feature_normal_at_point(
+        &self,
+        _feature: FeatureId,
+        _point: &Point<Real>,
+    ) -> Option<Unit<Vector<Real>>> {
+        #[cfg(feature = "dim2")]
+        return None;
+        #[cfg(feature = "dim3")]
+        return self.feature_normal(_feature);
+    }
+
     #[cfg(feature = "std")]
     fn as_composite_shape(&self) -> Option<&dyn SimdCompositeShape> {
         Some(self as &dyn SimdCompositeShape)

src/shape/trimesh.rs

@@ -848,6 +848,17 @@ impl TriMesh {
             )
         })
     }
+
+    #[cfg(feature = "dim3")]
+    /// Gets the normal of the triangle represented by `feature`.
+    pub fn feature_normal(&self, feature: FeatureId) -> Option<Unit<Vector<Real>>> {
+        match feature {
+            FeatureId::Face(i) => self
+                .triangle(i % self.num_triangles() as u32)
+                .feature_normal(FeatureId::Face(0)),
+            _ => None,
+        }
+    }
 }
 
 impl TriMesh {