Mimic mecanim's grid in background

You mean the AnimatorController grid? That's drawn using the GL API, see:

http://docs.unity3d.com/Documentation/ScriptReference/GL.LINES.html

Hard to know what colour, width, opacity you should use. The Mecanim grid is just black with different transparency for minor and major lines.

 

Wouldn't it be easier to use a tiled texture?

 

Here's some c#. Drop this grid.cs onto a camera. Think this is what you'll need.

Code (csharp):

1. //cs example
2. using UnityEngine;
3. using System.Collections;
4.  
5. public class grid : MonoBehaviour {
6.  
7.     private Rect m_LastGraphExtents;
8.         private static readonly Color kGridMinorColorDark  = new Color (0f, 0f, 0f, 0.18f);
9.         private static readonly Color kGridMajorColorDark  = new Color (0f, 0f, 0f, 0.28f);
10.  
11.     void Start () {
12.         CreateLineMaterial();
13.     }
14.    
15.     void OnGUI()
16.     {
17.         DrawGrid();
18.     }
19.    
20.     void DrawGrid ()
21.     {
22.         if (Event.current.type != EventType.Repaint)
23.             return;
24.  
25.         lineMaterial.SetPass(0);
26.        
27.         GL.PushMatrix ();
28.         GL.Begin (GL.LINES);
29.        
30.         DrawGridLines (10.0f, kGridMinorColorDark);
31.        
32.         DrawGridLines (50.0f, kGridMajorColorDark);
33.            
34.         GL.End ();
35.         GL.PopMatrix ();
36.        
37.     }
38.    
39.     private void DrawGridLines (float gridSize, Color gridColor)
40.     {
41.         GL.Color (gridColor);
42.         for (float x = 0.0f; x < Screen.width; x += gridSize)
43.             DrawLine (new Vector2 (x, 0.0f), new Vector2 (x, Screen.height));
44.         GL.Color (gridColor);
45.         for (float y = 0.0f; y < Screen.height; y += gridSize)
46.             DrawLine (new Vector2 (0.0f, y), new Vector2 (Screen.width, y));
47.     }
48.    
49.     private void DrawLine (Vector2 p1, Vector2 p2)
50.     {
51.         GL.Vertex (p1);
52.         GL.Vertex (p2);
53.     }
54.  
55.  
56.     private Material lineMaterial;
57.    
58.     private void CreateLineMaterial()
59.     {
60.         if( !lineMaterial ) {
61.             lineMaterial = new Material( "Shader \"Lines/Colored Blended\" {" +
62.                 "SubShader { Pass { " +
63.                 "    Blend SrcAlpha OneMinusSrcAlpha " +
64.                 "    ZWrite Off Cull Off Fog { Mode Off } " +
65.                 "    BindChannels {" +
66.                 "      Bind \"vertex\", vertex Bind \"color\", color }" +
67.                 "} } }" );
68.             lineMaterial.hideFlags = HideFlags.HideAndDontSave;
69.             lineMaterial.shader.hideFlags = HideFlags.HideAndDontSave;
70.         }
71.     }
72.  
73. }