Clones and flips a piece of geometry, optionally using another material

CloneAndFlipTriangles.cs

using UnityEngine;

// @kurtdekker
//
// Place on a MeshFilter / MeshRenderer GameObject.
//
//	This will:
//	- duplicate the entire GameObject via Instantiate
//		(and obviously its children; those are ignored!)
//	- parent it to the same place the original was
//	- clone the mesh
//	- flip all triangles in the mesh
//	- assign the mesh back to the MeshFilter
//	- optionally set the given new material in the Renderer

[RequireComponent( typeof( MeshFilter))]
public class CloneAndFlipTriangles : MonoBehaviour
{
	[Header( "Leave blank to use original materials.")]
	public Material ReplacementMaterial;

	void Awake()
	{
		GameObject original = gameObject;
		Transform parent = transform.parent;

		// keep us from going indefinitely!
		DestroyImmediate(this);

		GameObject copy = Instantiate<GameObject>(original, parent);

		MeshFilter mf = copy.GetComponent<MeshFilter>();

		Mesh mesh = Instantiate<Mesh>(mf.mesh);

		int[] originalTriangles = mesh.triangles;

		int triCount = originalTriangles.Length;
		int[] tris = new int[ triCount];

		for (int i = 0; i < triCount; i += 3)
		{
			// wind the triangles flipped the opposite way
			tris[i + 0] = originalTriangles[i + 0];
			tris[i + 1] = originalTriangles[i + 2];
			tris[i + 2] = originalTriangles[i + 1];
		}

		mesh.triangles = tris;

		mesh.RecalculateNormals ();

		mf.mesh = mesh;

		if (ReplacementMaterial)
		{
			Renderer mr = copy.GetComponent<Renderer>();

			mr.material = ReplacementMaterial;
		}
	}
}