fix: toCreasedNormals(): call toNonIndexed() only on non-indexed geometries

docs/examples/en/utils/BufferGeometryUtils.html

@@ -122,11 +122,19 @@ <h3>[method:BufferGeometry mergeVertices]( [param:BufferGeometry geometry], [par
 		</p>
 
 		<h3>[method:BufferGeometry toCreasedNormals]( [param:BufferGeometry geometry], [param:Number creaseAngle] )</h3>
+		<ul>
+			<li>geometry -- The input geometry.</li>
+			<li>creaseAngle -- The crease angle.</li>
+		</ul>
+
 		<p>
-		geometry -- The input geometry. <br />
-		creaseAngle -- The crease angle. <br /><br />
+		Modifies the supplied geometry if it is non-indexed, otherwise creates a new,
+		non-indexed geometry.
+		</p>
 
-		Creates a new, non-indexed geometry with smooth normals everywhere except faces that meet at an angle greater than the crease angle.
+		<p>
+		Returns the geometry with smooth normals everywhere except faces
+		that meet at an angle greater than the crease angle.
 		</p>
 
 		<h3>[method:BufferGeometry toTrianglesDrawMode]( [param:BufferGeometry geometry], [param:TrianglesDrawMode drawMode] )</h3>

docs/examples/zh/utils/BufferGeometryUtils.html

@@ -120,12 +120,19 @@ <h3>[method:BufferGeometry mergeVertices]( [param:BufferGeometry geometry], [par
 		</p>
 
 		<h3>[method:BufferGeometry toCreasedNormals]( [param:BufferGeometry geometry], [param:Number creaseAngle] )</h3>
+		<ul>
+			<li>geometry -- The input geometry.</li>
+			<li>creaseAngle -- The crease angle.</li>
+		</ul>
+
 		<p>
-			geometry -- The input geometry. <br />
-			creaseAngle -- The crease angle.
+			Modifies the supplied geometry if it is non-indexed, otherwise creates a new,
+			non-indexed geometry.
 		</p>
+
 		<p>
-		Creates a new, non-indexed geometry with smooth normals everywhere except faces that meet at an angle greater than the crease angle.
+			Returns the geometry with smooth normals everywhere except faces
+			that meet at an angle greater than the crease angle.
 		</p>
 
 		<h3>[method:BufferGeometry toTrianglesDrawMode]( [param:BufferGeometry geometry], [param:TrianglesDrawMode drawMode] )</h3>

examples/jsm/utils/BufferGeometryUtils.js

@@ -1229,8 +1229,22 @@ function mergeGroups( geometry ) {
 }
 
 
-// Creates a new, non-indexed geometry with smooth normals everywhere except faces that meet at
-// an angle greater than the crease angle.
+/**
+ * Modifies the supplied geometry if it is non-indexed, otherwise creates a new,
+ * non-indexed geometry. Returns the geometry with smooth normals everywhere except
+ * faces that meet at an angle greater than the crease angle.
+ *
+ * Backwards compatible with code such as @react-three/drei's `<RoundedBox>`
+ * which uses this method to operate on the original geometry.
+ *
+ * As of this writing, BufferGeometry.toNonIndexed() warns if the geometry is
+ * non-indexed and returns `this`, i.e. the same geometry on which it was called:
+ * `BufferGeometry is already non-indexed.`
+ *
+ * @param {BufferGeometry} geometry
+ * @param {number} [creaseAngle]
+ * @return {BufferGeometry}
+ */
 function toCreasedNormals( geometry, creaseAngle = Math.PI / 3 /* 60 degrees */ ) {
 
 	const creaseDot = Math.cos( creaseAngle );
@@ -1253,7 +1267,7 @@ function toCreasedNormals( geometry, creaseAngle = Math.PI / 3 /* 60 degrees */
 
 	}
 
-	const resultGeometry = geometry.toNonIndexed();
+	const resultGeometry = geometry.index ? geometry.toNonIndexed() : geometry;
 	const posAttr = resultGeometry.attributes.position;
 	const vertexMap = {};