Mouse click model is determined, the material in contact with the mouse

When a MeshRenderer have more than one material, with the sub-index grid index in the corresponding MeshRenderer.materials, so just need to find the sub-index of the grid will be able to find the index of the material.

using UnityEngine;

public class TestRaycastHitMaterial:MonoBehaviour{
    
    private void Update() {
        if(!Input.GetMouseButtonDown(0))return;
        var meshRenderer=GetComponent<MeshRenderer>();
        var meshFilter=GetComponent<MeshFilter>();
        var mesh=meshFilter.mesh;

        var ray=Camera.main.ScreenPointToRay(Input.mousePosition);
        RaycastHit hitInfo;
        Physics.Raycast(ray,out hitInfo);

        if(hitInfo.collider!=null){
            int subMeshIndex=MeshUtil.getRaycastHitSubMeshIndex(mesh,hitInfo);
            Debug.Log(subMeshIndex);
            //Debug.Log(meshRenderer.materials[subMeshIndex]);
        }
    }

    /// <summary>
    /// 返回射线命中的子网格索引号
    /// <br>如果没有子网格或未成功匹配则返回-1</br>
    /// </summary>
    /// <param name="mesh"></param>
    /// <param name="hitInfo"></param>
    /// <returns></returns>
    private int getRaycastHitSubMeshIndex(Mesh mesh,RaycastHit hitInfo){
        //命中三角形的顶点索引
        int[] triangles=mesh.triangles;
        int triangleIndex=hitInfo.triangleIndex;
        int i0=triangles[triangleIndex*3];
        int i1=triangles[triangleIndex*3+1];
        int i2=triangles[triangleIndex*3+2];
        
        int subMeshCount=mesh.subMeshCount;
        for(int i=0;i<subMeshCount;i++){
            var indices=mesh.GetIndices(i);
            int vertexCount=indices.Length;
            for(int j=0;j<vertexCount;j+=3){
                int j0=indices[j];
                int j1=indices[j+1];
                int j2=indices[j+2];
                //如果子网格的索引与命中三角形匹配，则表示是命中的子网格
                if(i0==j0&&i1==j1&&i2==j2){
                    return i;
                }
            }
        }
        return -1;
    }
}