RaycastHit.textureCoord2

Description

The secondary uv texture coordinate at the impact point.

This can be used for 3D texture painting or drawing bullet marks. If the collider is not a mesh collider, Vector2.zero will be returned. If the mesh contains no secondary uv set, the uv of the primary uv set will be returned.

// Attach this script to a camera and it will paint black pixels in 3D
// on whatever the user clicks. Make sure the mesh you want to paint
// on has a mesh collider attached.

var cam: Camera;

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

function Update () {
    // Only when we press the mouse
    if (!Input.GetMouseButton (0))
        return;

    // Only if we hit something, do we continue
    var hit : RaycastHit;
    if (!Physics.Raycast(cam.ScreenPointToRay(Input.mousePosition), hit))
        return;

    // Just in case, also make sure the collider also has a renderer
    // material and texture. Also we should ignore primitive colliders.
    var rend: Renderer = hit.transform.GetComponent.<Renderer>();
    var meshCollider = hit.collider as MeshCollider;

    if (rend == null || rend.sharedMaterial == null ||
        rend.sharedMaterial.mainTexture == null || meshCollider == null)
        return;

    // Now draw a pixel where we hit the object
    var tex : Texture2D = rend.material.mainTexture as Texture2D;
    var pixelUV : Vector2 = hit.textureCoord2;
    pixelUV.x *= tex.width;
    pixelUV.y *= tex.height;

    tex.SetPixel(Mathf.FloorToInt(pixelUV.x), Mathf.FloorToInt(pixelUV.y), Color.black);

    tex.Apply();
}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public Camera cam;
    void Start() {
        cam = GetComponent<Camera>();
    }
    void Update() {
        if (!Input.GetMouseButton(0))
            return;
        
        RaycastHit hit;
        if (!Physics.Raycast(cam.ScreenPointToRay(Input.mousePosition), out hit))
            return;
        
        Renderer rend = hit.transform.GetComponent<Renderer>();
        MeshCollider meshCollider = hit.collider as MeshCollider;
        if (rend == null || rend.sharedMaterial == null || rend.sharedMaterial.mainTexture == null || meshCollider == null)
            return;
        
        Texture2D tex = rend.material.mainTexture as Texture2D;
        Vector2 pixelUV = hit.textureCoord2;
        pixelUV.x *= tex.width;
        pixelUV.y *= tex.height;
        tex.SetPixel(Mathf.FloorToInt(pixelUV.x), Mathf.FloorToInt(pixelUV.y), Color.black);
        tex.Apply();
    }
}