Calclate Tangents.

Assets/IcoSphereCreator/IcoSphereCreator.cs

@@ -113,6 +113,7 @@ public static Mesh Create(int n, float radius)
         mesh.triangles = triangles;
         mesh.uv = uv;
         mesh.RecalculateNormals();
+        CreateTangents(mesh);
 
         return mesh;
     }
@@ -157,4 +158,76 @@ static void CreateUV(int n, Vector3[] vertices, Vector2[] uv)
         uv[7 * tt + 0].x = 0.625f;
 
     }
+
+    static void CreateTangents(Mesh mesh)
+    {
+        int[] triangles = mesh.triangles;
+        Vector3[] vertices = mesh.vertices;
+        Vector2[] uv = mesh.uv;
+        Vector3[] normals = mesh.normals;
+
+        int triangleCount = triangles.Length;
+        int vertexCount = vertices.Length;
+
+        Vector3[] tan1 = new Vector3[vertexCount];
+        Vector3[] tan2 = new Vector3[vertexCount];
+
+        Vector4[] tangents = new Vector4[vertexCount];
+
+        for (int i = 0; i < triangleCount; i += 3)
+        {
+            int i1 = triangles[i + 0];
+            int i2 = triangles[i + 1];
+            int i3 = triangles[i + 2];
+
+            Vector3 v1 = vertices[i1];
+            Vector3 v2 = vertices[i2];
+            Vector3 v3 = vertices[i3];
+
+            Vector2 w1 = uv[i1];
+            Vector2 w2 = uv[i2];
+            Vector2 w3 = uv[i3];
+
+            float x1 = v2.x - v1.x;
+            float x2 = v3.x - v1.x;
+            float y1 = v2.y - v1.y;
+            float y2 = v3.y - v1.y;
+            float z1 = v2.z - v1.z;
+            float z2 = v3.z - v1.z;
+
+            float s1 = w2.x - w1.x;
+            float s2 = w3.x - w1.x;
+            float t1 = w2.y - w1.y;
+            float t2 = w3.y - w1.y;
+
+            float r = 1.0f / (s1 * t2 - s2 * t1);
+
+            Vector3 sdir = new Vector3((t2 * x1 - t1 * x2) * r, (t2 * y1 - t1 * y2) * r, (t2 * z1 - t1 * z2) * r);
+            Vector3 tdir = new Vector3((s1 * x2 - s2 * x1) * r, (s1 * y2 - s2 * y1) * r, (s1 * z2 - s2 * z1) * r);
+
+            tan1[i1] += sdir;
+            tan1[i2] += sdir;
+            tan1[i3] += sdir;
+
+            tan2[i1] += tdir;
+            tan2[i2] += tdir;
+            tan2[i3] += tdir;
+        }
+
+
+        for (int i = 0; i < vertexCount; ++i)
+        {
+            Vector3 n = normals[i];
+            Vector3 t = tan1[i];
+
+            Vector3.OrthoNormalize(ref n, ref t);
+            tangents[i].x = t.x;
+            tangents[i].y = t.y;
+            tangents[i].z = t.z;
+
+            tangents[i].w = (Vector3.Dot(Vector3.Cross(n, t), tan2[i]) < 0.0f) ? -1.0f : 1.0f;
+        }
+
+        mesh.tangents = tangents;
+    }
 }