RaycastHit.triangleIndex

Description

The index of the triangle that was hit.

Triangle index is only valid if the collider that was hit is a MeshCollider.

// This script draws a debug line around mesh triangles
// This script draws a debug line around mesh triangles
// as you move the mouse over them.

#pragma strict

var cam: Camera;

function Start() {
    cam = GetComponent.<Camera>();
}

function Update() {
    var hit: RaycastHit;

    if (!Physics.Raycast(cam.ScreenPointToRay(Input.mousePosition), hit))
        return ;

    var meshCollider: MeshCollider = hit.collider as MeshCollider;
    if (meshCollider == null || meshCollider.sharedMesh == null)
        return ;

    var mesh: Mesh = meshCollider.sharedMesh;
    var vertices: Vector3[] = mesh.vertices;
    var triangles: int[] = mesh.triangles;
    var p0: Vector3 = vertices[triangles[hit.triangleIndex * 3 + 0]];
    var p1: Vector3 = vertices[triangles[hit.triangleIndex * 3 + 1]];
    var p2: Vector3 = vertices[triangles[hit.triangleIndex * 3 + 2]];
    var hitTransform: Transform = hit.collider.transform;

    p0 = hitTransform.TransformPoint(p0);
    p1 = hitTransform.TransformPoint(p1);
    p2 = hitTransform.TransformPoint(p2);

    Debug.DrawLine(p0, p1);
    Debug.DrawLine(p1, p2);
    Debug.DrawLine(p2, p0);
}

// This script draws a debug line around mesh triangles
// as you move the mouse over them.
using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    Camera camera;

    void Start()
    {
        camera = GetComponent<Camera>();
    }

    void Update()
    {
        RaycastHit hit;
        if (!Physics.Raycast(camera.ScreenPointToRay(Input.mousePosition), out hit))
            return;

        MeshCollider meshCollider = hit.collider as MeshCollider;
        if (meshCollider == null || meshCollider.sharedMesh == null)
            return;

        Mesh mesh = meshCollider.sharedMesh;
        Vector3[] vertices = mesh.vertices;
        int[] triangles = mesh.triangles;
        Vector3 p0 = vertices[triangles[hit.triangleIndex * 3 + 0]];
        Vector3 p1 = vertices[triangles[hit.triangleIndex * 3 + 1]];
        Vector3 p2 = vertices[triangles[hit.triangleIndex * 3 + 2]];
        Transform hitTransform = hit.collider.transform;
        p0 = hitTransform.TransformPoint(p0);
        p1 = hitTransform.TransformPoint(p1);
        p2 = hitTransform.TransformPoint(p2);
        Debug.DrawLine(p0, p1);
        Debug.DrawLine(p1, p2);
        Debug.DrawLine(p2, p0);
    }
}

See Also: Physics.Raycast, Physics.Linecast, Physics.RaycastAll.