Problem creating a circle mesh

from the comments : http://answers.unity3d.com/questions/597849/shader-wants-tangents-but-the-mesh-doesnt-have-the-1.html#answer-597899

• have already seen this link, but it didn't worked :(*

Possibly because you are coding in uJS and the script is in C#. If you havn't put the TangentSolver in a special folder as per compilation order to be recognized.

Here is your script with a line added to use the class (tested and working) :

 #pragma strict
 
 var l : int = 50;
 var x : float;
 var y : float;
 
 function Start() 
 {
     var verts: Vector3[] = new Vector3[361];
     var normals: Vector3[] = new Vector3[361];
     var uv: Vector2[] = new Vector2[361];
     var tri: int[] = new int[1080];
 
     var mf: MeshFilter = GetComponent(MeshFilter);
 
     verts[0] = new Vector3(0, 0, 0);
     uv[0] = new Vector3(0, 0);
     for (var i : int = 1;i<361;i++) { // For each degrees
         x = Mathf.Cos(i) * l; // I calc the position
         y = Mathf.Sin(i) * l;
         verts[i] = new Vector3(x, 0, y); // and assign vertices, uv, normals, etc..
         uv[i] = new Vector3(x, y);
         tri[(i-1)*3] = 0; // I don't know if triangles should work like this,
         tri[(i-1)*3+1] = i; // here I think that triangle is the index of a vertice
         if ((i+1 > 360)) {
             tri[(i-1)*3 + 2] = 1;
         } else {
             tri[(i-1)*3 + 2] = i+1;
         }
     }
 
     for (i = 0; i < normals.Length; i++) {
         normals[i] = Vector3.up;
     }
 
     var mesh: Mesh = new Mesh();
     mesh.vertices = verts;
     mesh.triangles = tri;
     mesh.uv = uv;
     mesh.normals = normals;
     
     // Calculate Tangents
     TangentSolver(mesh);
 
     mf.mesh = mesh;
 }

There is something not right about the way you are calculating the triangles. You can have a look at my answer here for another way to create a circle/ring mesh : http://answers.unity3d.com/questions/375604/expanding-ring-velocity-ellipsoid-particle-emitter.html

As you are working in uJS, to avoid compilation problems, here is my uJS version of the TangentSolver :

 /*
 Derived from
 Lengyel, Eric. “Computing Tangent Space Basis Vectors for an Arbitrary Mesh”. Terathon Software 3D Graphics Library, 2001.
 [url]http://www.terathon.com/code/tangent.html[/url]
 */
 
 class TangentSolver
 {
     function TangentSolver(theMesh : Mesh)
     {
         var vertexCount = theMesh.vertexCount;
         var vertices = theMesh.vertices;
         var normals = theMesh.normals;
         var texcoords = theMesh.uv;
         var triangles = theMesh.triangles;
         var triangleCount = triangles.length/3;
         var tangents = new Vector4[vertexCount];
         var tan1 = new Vector3[vertexCount];
         var tan2 = new Vector3[vertexCount];
         var tri = 0;
 
         for (var  i:int = 0; i < (triangleCount); i++)
         {
             var i1 = triangles[tri];
             var i2 = triangles[tri+1];
             var i3 = triangles[tri+2];
 
             var v1 = vertices[i1];
             var v2 = vertices[i2];
             var v3 = vertices[i3];
 
             var w1 = texcoords[i1];
             var w2 = texcoords[i2];
             var w3 = texcoords[i3];
 
             var x1 = v2.x - v1.x;
             var x2 = v3.x - v1.x;
             var y1 = v2.y - v1.y;
             var y2 = v3.y - v1.y;
             var z1 = v2.z - v1.z;
             var z2 = v3.z - v1.z;
 
             var s1 = w2.x - w1.x;
             var s2 = w3.x - w1.x;
             var t1 = w2.y - w1.y;
             var t2 = w3.y - w1.y;
 
             var r = 1.0 / (s1 * t2 - s2 * t1);
             var sdir = new Vector3((t2 * x1 - t1 * x2) * r, (t2 * y1 - t1 * y2) * r, (t2 * z1 - t1 * z2) * r);
             var 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;
 
             tri += 3;
         }
 
         for (i = 0; i < (vertexCount); i++)
         {
             var n = normals[i];
             var t = tan1[i];
 
             // Gram-Schmidt orthogonalize
             Vector3.OrthoNormalize( n, t );
 
             tangents[i].x  = t.x;
             tangents[i].y  = t.y;
             tangents[i].z  = t.z;
 
             // Calculate handedness
             tangents[i].w = ( Vector3.Dot(Vector3.Cross(n, t), tan2[i]) < 0.0 ) ? -1.0 : 1.0;
         }     
         
         theMesh.tangents = tangents;
     }
 }