MeshDisplay.cs

using UnityEngine;
using System.Collections;

/// <summary>
/// Utility class that let you see normals and tangent vectors for a mesh.
/// This is really useful when debugging mesh appearance
/// </summary>
[RequireComponent (typeof (MeshFilter))]
public class MeshDisplay : MonoBehaviour {
	public bool showNormals = true;
	public bool showTangents = true;
	public float displayLengthScale = 1.0f;
	
	public Color normalColor = Color.red;
	public Color tangentColor = Color.blue;
	
	void OnDrawGizmosSelected() {
		MeshFilter meshFilter = GetComponent<MeshFilter>();
		if (meshFilter==null){
			Debug.LogWarning("Cannot find MeshFilter");
			return;
		}
		Mesh mesh = meshFilter.sharedMesh;
		if (mesh==null){
			Debug.LogWarning("Cannot find mesh");
			return;
		}
        bool doShowNormals = showNormals && mesh.normals.Length==mesh.vertices.Length;
        bool doShowTangents = showTangents && mesh.tangents.Length==mesh.vertices.Length;

		foreach (int idx in mesh.triangles){
			Vector3 vertex = transform.TransformPoint(mesh.vertices[idx]);
			
			if (doShowNormals){
				Vector3 normal = transform.TransformDirection(mesh.normals[idx]);
				Gizmos.color = normalColor;
				Gizmos.DrawLine(vertex, vertex+normal*displayLengthScale);
			}
			if (doShowTangents){
				Vector3 tangent = transform.TransformDirection(mesh.tangents[idx]);
				Gizmos.color = tangentColor;
				Gizmos.DrawLine(vertex, vertex+tangent*displayLengthScale);
			}
		}    
    }
}