Get vertices a material is assigned to

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Hello! As the title states I am after a solution on how i can get all the vertices that a material is assigned to. T$$anonymous$$s because I want to be able to change the vertex colors just for that part. The reason being is that I'm creating a mobile game with cars, where I only want 1 draw call for the body, but i still want the ability to change color of the car at runtime, except windows, lights, grill etc (so I can't use a shader with a main color, and i don't want 2 materials for the body). So if I somehow can save a list with these vertices would be great.

Thanks in advance

Answer 1

Answer by richyrich · Oct 21, 2014 at 02:59 PM

Your question relates to sub meshes...

In order to have multiple materials, your mesh will have multiple sub-meshes - one for each material. On that basis, you could use the function GetTriangles to obtain all the triangles for a given sub-mesh. You would then loop through and identify all unique vertex indices used wit$$anonymous$$n the array.

See http://docs.unity3d.com/ScriptReference/Mesh.GetTriangles.html for more information

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_dns_ · Oct 21, 2014 at 03:23 PM 0

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Hi, this would work but I think having sub-meshes makes multiple drawcall (maybe not all the time but that's what happened on my projects/tests). If it does, I would then use your solution of creating sub-meshes for authoring the meshes. Then, I would create some editor code to merge the sub-meshes into one mesh that is used in the game. This merging code would have everything it needs to create an array of index of vertices that needs a color change. Maybe you can just store the vertices that needs a color change first in the mesh, then have to store only 1 index to know when to stop changing vertex colors later.

orcinusdev · Oct 21, 2014 at 03:27 PM 0

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Thank you for an answer. Yes i read about GetTriangles just after posting this. But GetTriangles returns a Int[] (I guess this is some kind of index) while mesh.vertices is a Vector3[] (actual positions). Which function let me loop though all vertex indices and store them in a vertices array?

orcinusdev · Oct 21, 2014 at 03:32 PM 0

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@_dns

It was exactly what I was thinking about. First by have them separate i can identify the vertices, and change specified vertex colors. It would be great. And then combine everything to one mesh with 1 material.

_dns_ · Oct 21, 2014 at 03:45 PM 0

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yes, GetTriangles returns a, int[] composed of indexes of vertices from the .vertices array, 3 indexes per triangle. Maybe you can check this code to create your own: http://wiki.unity3d.com/index.php?title=MeshMerger. You may also want to save your created mesh to disk using http://docs.unity3d.com/ScriptReference/AssetDatabase.CreateAsset.html so you can use it like any other mesh.

Bunny83 · Oct 21, 2014 at 03:51 PM 0

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@orcinusdev: A mesh consists of vertices and indices. The vertices i talk about includes all the arrays related to vertex attributes. So the .vertices, .normals, .uv, .colors, ... arrays all made up the vertices list. A mesh only has one vertices array but might have multiple submeshes. GetTriangles will return the indices for the given material / submesh index. The returned indices array contains the actual triangle definition. So it's count is always a multiple of 3. Those indices index into the vertices arrays.

So if you want to change the vertex color of all vertices that belong to the submesh 1 just use GetTriangles(1) and iterate through that array and change the meshs colors[index] to your desired color.

Note: Keep in mind that if two submeshes share the same vertices (which is quite unusual but possible) you can't change the color just for one submesh without affecting the other. The only way in such a case is to manually duplicate the shared vertices.

To collapse all submeshes into one all you have to do is:

 mesh.triangles = mesh.triangles;

This will keep all triangles but merge them into one submesh and will remove all others.

Answer 2

TY for the help, here is a working solution

 using UnityEngine;
 using System.Collections;
 
 public class ChangeColor : MonoBehaviour {
 
     // T$$anonymous$$s code replaces the indexed submesh and corresponding material color to a vertex color. Then it combines all materials to a single material (Only tested for 2 materials)
 
 
     Color newColor;
     public Shader vertexColoredShader;
     public Texture lightmap;
     public int subMeshNumber = 1;
 
     // Use t$$anonymous$$s for initialization
     void Start () {
         Mesh mesh = GetComponent<MeshFilter>().mesh;
 
         newColor = renderer.materials[subMeshNumber].GetColor("_Color");
 
         Debug.Log("Submeshes: " + mesh.subMeshCount);
         int[] t = mesh.GetTriangles(subMeshNumber);
         Vector3[] vertices = mesh.vertices;
         Color[] oldColors = mesh.colors;
         Color[] colors = new Color[vertices.Length];
         for (int i = 0; i < vertices.Length; i++)
         {
 
             bool foundSubMeshV = false;
 
             foreach (int index in t)
             {
 
                 if (i == index)
                 {
                     colors[i] = newColor;
                     foundSubMeshV = true;
                 }
 
             
 
             }
 
             if(foundSubMeshV)
                 continue;
 
 
             colors[i] = oldColors[i];
         }
             
 
 
         mesh.colors = colors;
         mesh.triangles = mesh.triangles;
 
         DestroyImmediate(renderer);
         gameObject.AddComponent<MeshRenderer>();
 
 
         Material newMat = new Material (vertexColoredShader);
         renderer.material = newMat;
         if(lightmap)
         renderer.material.mainTexture = lightmap;
 
 
 
     
 
 
     
     }
 }

Get vertices a material is assigned to

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