Take a flat 2d poly mesh and return a mesh with MeshTopology.Lines of the outline. Good for text!

Outliner.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class Outliner : BaseBehaviour
{
	void Awake()
	{
		GetComponent<MeshFilter>().mesh
			= FindOutlinePairs(GetComponent<MeshFilter>().mesh);
	}
	Mesh FindOutlinePairs(Mesh mesh)
	{
		var edges = new Dictionary<KeyValuePair<int, int>, int>();

		for (int i = 0; i < mesh.triangles.Length; i += 3)
		{
			int idx1 = mesh.triangles[i];
			int idx2 = mesh.triangles[i+1];
			int idx3 = mesh.triangles[i+2];

			KeyValuePair<int,int> a;
			KeyValuePair<int,int> b;
			KeyValuePair<int,int> c;

			if (idx1 < idx2)
				a = new KeyValuePair<int,int>(idx1, idx2);
			else
				a = new KeyValuePair<int,int>(idx2, idx1);
			if (idx2 < idx3)
				b = new KeyValuePair<int,int>(idx2, idx3);
			else
				b = new KeyValuePair<int,int>(idx3, idx2);
			if (idx3 < idx1)
				c = new KeyValuePair<int,int>(idx3, idx1);
			else
				c = new KeyValuePair<int,int>(idx1, idx3);

			if (!edges.ContainsKey(a)) edges[a] = 0;
			if (mesh.colors[idx1] == Color.white && mesh.colors[idx2] == Color.white)
				edges[a] += 1;
			if (!edges.ContainsKey(b)) edges[b] = 0;
			if (mesh.colors[idx2] == Color.white && mesh.colors[idx3] == Color.white)
				edges[b] += 1;
			if (!edges.ContainsKey(c)) edges[c] = 0;
			if (mesh.colors[idx3] == Color.white && mesh.colors[idx1] == Color.white)
				edges[c] += 1;
		}

		var indices = new List<int>();
		// Find all the edges with only 1 or two edges
		foreach (var pair in edges)
		{
			if (pair.Value == 1)
			{
				indices.Add(pair.Key.Key);
				indices.Add(pair.Key.Value);
			}
		}


		var newMesh = new Mesh();
		newMesh.vertices = mesh.vertices;
		newMesh.SetIndices(indices.ToArray(), MeshTopology.Lines, 0);

		return newMesh;
	}
}