Change generate_outline_normals() not to if they equal regular normals.

src/lib.rs

@@ -67,8 +67,12 @@ pub enum GenerateOutlineNormalsError {
     InvalidVertexAttributeFormat(&'static str, VertexFormat, VertexFormat),
 }
 
+/// Extension methods for [`Mesh`].
 pub trait OutlineMeshExt {
     /// Generates outline normals for the mesh by normalising the sum of the regular normals.
+    ///
+    /// This function will silently do nothing if the outline normals would be equal to the
+    /// regular normals.
     fn generate_outline_normals(&mut self) -> Result<(), GenerateOutlineNormalsError>;
 }
 
@@ -95,11 +99,18 @@ impl OutlineMeshExt for Mesh {
             )),
         }?;
         let mut map = HashMap::with_capacity(positions.len());
+        let mut modified = false;
         for (p, n) in positions.iter().zip(normals.iter()) {
             let key = [FloatOrd(p[0]), FloatOrd(p[1]), FloatOrd(p[2])];
             let value = Vec3::from_array(*n);
-            map.entry(key).and_modify(|e| *e += value).or_insert(value);
+            map.entry(key)
+                .and_modify(|e| {
+                    modified = true;
+                    *e += value
+                })
+                .or_insert(value);
         }
+        if modified {
             let mut outlines = Vec::with_capacity(positions.len());
             for p in positions.iter() {
                 let key = [FloatOrd(p[0]), FloatOrd(p[1]), FloatOrd(p[2])];
@@ -109,6 +120,7 @@ impl OutlineMeshExt for Mesh {
                 ATTRIBUTE_OUTLINE_NORMAL,
                 VertexAttributeValues::Float32x3(outlines),
             );
+        }
         Ok(())
     }
 }