RaycastHit.textureCoord2

説明

衝突したセカンダリ UV テクスチャの座標

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.

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();
    }
}