Cube や Sphere の内壁で衝突判定したい ref: http://qiita.com/_meki/items/b5c12eeee125d868e92d

InvertedSphere.cs

     using UnityEngine;
     using UnityEditor;

     public class InvertedSphere : EditorWindow {
         private string st = "1.0";

         [MenuItem("GameObject/Create Other/Inverted Sphere...")]
         public static void ShowWindow() {
             EditorWindow.GetWindow(typeof(InvertedSphere));
         }

         public void OnGUI() {
             GUILayout.Label("Enter sphere size:");
             st = GUILayout.TextField (st);

             float f;
             if (!float.TryParse (st, out f))
                 f = 1.0f;
             if (GUILayout.Button("Create Inverted Sphere")) {
                 CreateInvertedSphere(f);
             }
         }

         private void CreateInvertedSphere(float size) {
             GameObject go = GameObject.CreatePrimitive(PrimitiveType.Sphere);
             MeshFilter mf = go.GetComponent<MeshFilter>();
             Mesh mesh = mf.sharedMesh;

             GameObject goNew = new GameObject();    
             goNew.name = "Inverted Sphere";
             MeshFilter mfNew = goNew.AddComponent<MeshFilter>();
             mfNew.sharedMesh = new Mesh();


             //Scale the vertices;
             Vector3[] vertices = mesh.vertices;
             for (int i = 0; i < vertices.Length; i++)
                 vertices[i] = vertices[i] * size;
             mfNew.sharedMesh.vertices = vertices;

             // Reverse the triangles
             int[] triangles = mesh.triangles;
             for (int i = 0; i < triangles.Length; i += 3) {
                 int t = triangles[i];
                 triangles[i] = triangles[i+2];
                 triangles[i+2] = t;
             }
             mfNew.sharedMesh.triangles = triangles;

             // Reverse the normals;
             Vector3[] normals = mesh.normals;
             for (int i = 0; i < normals.Length; i++)
                 normals[i] = -normals[i];
             mfNew.sharedMesh.normals = normals;


             mfNew.sharedMesh.uv = mesh.uv;
             mfNew.sharedMesh.uv2 = mesh.uv2;
             mfNew.sharedMesh.RecalculateBounds();

             // メモ： 下記３行は Unity 5.0.2 ではコンパイルエラーになりました。まるごと削除すれば普通に使えます。
             // Add the same material that the original sphere used
             MeshRenderer mr = goNew.AddComponent<MeshRenderer>();
             mr.sharedMaterial = go.renderer.sharedMaterial;

             DestroyImmediate(go);
         }
     }