Pack textures on mesh with multiple submeshes

Hi. I'm doing some optimization stuff and trying to pack all materials to one material. Here's my problem: I have mesh with 5 submeshes(5 materials with different textures). I can pack all textures to one atlas and use just that texture. Problem is I don't know how to recalculate new uvs to my new atlas. Here's the code:

Code (csharp):

1.  
2. private void CreateMeshTexture ()
3.  {  
4.        //get all textures
5.        var rend = renderer;
6.        var atlasMaterial = new Material (Shader.Find ("Mobile/Diffuse"));
7.        var meshFilter = GetComponent<MeshFilter> ();
8.        var textures = new List<Texture2D> ();
9.  
10.        foreach (var mat in rend.materials) {
11.          textures.Add ((Texture2D)mat.mainTexture);
12.        }
13.  
14.  
15.        //create texture atlas
16.        textureAtlas = new Texture2D (maxSquareTextureSize, maxSquareTextureSize);
17.        Rect[] coords = textureAtlas.PackTextures (textures.ToArray (), 0, maxSquareTextureSize);  
18.        atlasMaterial.mainTexture = textureAtlas;
19.  
20.        //update materials
21.        rend.material = atlasMaterial;
22.        for (int i = 0; i < rend.materials.Length; ++i) {
23.          rend.materials[i] = atlasMaterial;
24.        }
25.  
26.        //correct uvs
27.        Vector2[] oldUV, newUV;
28.        oldUV = meshFilter.mesh.uv;
29.        newUV = new Vector2[oldUV.Length];
30.  
31.        //how to set new uvs?
32.  
33.  }
34.  

How to recalculate uvs?

 

It depends on how you creating atlas texture. Let's create some example of created atlas.
Well, imaging very simple atlas texture, it's created from 4 texture. 2 textures on each side;



So, full atlas texture uvs are spread from 0(uv0) to 1(uv1) by width, and from 0(uv0) to 1(uv1).
You only need to set new uvs meshes. e.g. for mesh0 (that uses Tex0) you need to set texture uv from "uv0" to "a" by width, and from "uv0" to "b" by height.

Of course it's very simple example, but you only need to understand how do you place your textures

 

Yeah, I knew that. Problem was I couldn't know from which texture uv was taken. I've solved my problem by dividing all submeshes to different meshes and combining them later. Here's the code:

Code (csharp):

1.  
2. private Vector2 UVwithOffset(Vector2 oldUV, Rect rect)
3.     {
4.         var newUV = new Vector2();
5.         newUV.x = Mathf.Lerp(rect.xMin, rect.xMax, oldUV.x);
6.         newUV.y = Mathf.Lerp(rect.yMin, rect.yMax, oldUV.y);
7.         return newUV;
8.     }
9.  
10.  
11.     private Mesh CreateMesh(Mesh oldMesh, int subIndex, Rect uvOffset)
12.     {
13.         var newMesh = new Mesh();
14.  
15.         var triangles = new List<int>();
16.         triangles.AddRange(oldMesh.GetTriangles(subIndex)); // the triangles of the sub mesh
17.         var trianglesHashSet = new HashSet<int>(triangles);
18.  
19.         var newVertices = new List<Vector3>();
20.         var newUvs = new List<Vector2>();
21.  
22.         var oldToNewIndices = new Dictionary<int, int>();
23.         int newIndex = 0;
24.  
25.         // Collect the vertices and uvs
26.         for (int i = 0; i < oldMesh.vertices.Length; i++) {
27.             if (!trianglesHashSet.Contains(i)) continue;
28.             newVertices.Add(oldMesh.vertices[i]);
29.             newUvs.Add(UVwithOffset(oldMesh.uv[i], uvOffset));
30.             oldToNewIndices.Add(i, newIndex);
31.             ++newIndex;
32.         }
33.  
34.         var newTriangles = new int[triangles.Count];
35.         for (int i = 0; i < newTriangles.Length; i++) {
36.             newTriangles[i] = oldToNewIndices[triangles[i]];
37.         }
38.         newMesh.vertices = newVertices.ToArray();
39.         newMesh.uv = newUvs.ToArray();
40.         newMesh.triangles = newTriangles;
41.         newMesh.RecalculateBounds();
42.         newMesh.RecalculateNormals();
43.  
44.         return newMesh;
45.     }

Thank you for help.

 

Well done!

And what about performance in result scene? It's ok?

>Problem was I couldn't know from which texture uv was taken.
Maybe solution is to store a dictionary such as <texture_atlas_region_uv, texture>. Or something like that?

But, I like your solution

 

You're absolutely right. Moreover, dividing submeshes into meshes isn't nessecary, I can just update uvs in mesh and then combine only itself to merge their submeshes to single submesh.

I didn't write it yet, maybe in a weekend I'll finish with that and share with community.

Thank you very much.

p.s. How I can change topic's title? I want to put [SOLVED] tag