Makes geometry double-sided by re-winding copies of each triangle to face the other way

MakeGeometryDoubleSided.cs

using UnityEngine;

// @kurtdekker - quick double-siding mechanism.
//
// Place or add this Component to things with at
// least a MeshFilter on them.
//
// Presently only for single-submesh geometry.

[RequireComponent( typeof( MeshFilter))]
public class MakeGeometryDoubleSided : MonoBehaviour
{
	void Awake()
	{
		MeshFilter mf = GetComponent<MeshFilter>();

		// If this blows up you failed to meet the documented
		// requirement above that a MeshFilter be present.
		int vertCount = mf.mesh.vertices.Length;

		// we need to dupe all verts so we can have lighting / UV info
		Vector3[] verts = new Vector3[ vertCount * 2];
		for (int i = 0; i < vertCount; i++)
		{
			verts [i] = mf.mesh.vertices [i];
			verts [i + vertCount] = mf.mesh.vertices [i];
		}

		// and of course dupe all triangles
		int triCount = mf.mesh.triangles.Length;
		int[] tris = new int[ triCount * 2];

		for (int i = 0; i < triCount; i += 3)
		{
			// re-add the original triangles, no change
			tris[i + 0] = mf.mesh.triangles[i + 0];
			tris[i + 1] = mf.mesh.triangles[i + 1];
			tris[i + 2] = mf.mesh.triangles[i + 2];

			// now add triangles flipped the opposite way
			tris[i + triCount + 0] = mf.mesh.triangles[i + 0] + vertCount;
			tris[i + triCount + 1] = mf.mesh.triangles[i + 2] + vertCount;
			tris[i + triCount + 2] = mf.mesh.triangles[i + 1] + vertCount;
		}

		mf.mesh.vertices = verts;

		mf.mesh.triangles = tris;

		mf.mesh.RecalculateNormals ();
	}
}