unity 在模型上绘画

using UnityEngine;
/// <summary>
/// 在模型上绘画
/// </summary>
public class DrawOnModel:BaseMonoBehaviour{
    [Tooltip("颜色")]
    public Color color=Color.cyan;
    [Tooltip("笔刷大小")]
    public float brushSize=10f;
    private Camera m_mainCamera;
    private Texture2D m_texture2D;
    protected override void Awake(){
        base.Awake();
        m_mainCamera=Camera.main;
        //创建一个副本，避免修改原纹理
        Renderer renderer=GetComponent<Renderer>();
        Texture2D mainTexture=(Texture2D)renderer.material.mainTexture;
        Texture2D tempTexture2D=new Texture2D(mainTexture.width,mainTexture.height);
        tempTexture2D.SetPixels(mainTexture.GetPixels());
        tempTexture2D.Apply();
        renderer.material.mainTexture=tempTexture2D;
        m_texture2D=tempTexture2D;
    }

    protected override void Update2(){
        base.Update2();
        if(Input.GetMouseButton(0)){
            RaycastHit[] raycastHits=new RaycastHit[1];
            Physics.RaycastNonAlloc(m_mainCamera.ScreenPointToRay(Input.mousePosition),raycastHits);
            var hit=raycastHits[0];
            if(hit.collider!=null&&hit.collider.gameObject==gameObject){
                DrawCircleDot(hit.textureCoord,m_texture2D,color,brushSize);
                //DrawRectDot(hit.textureCoord,m_texture2D,color,brushSize);
            }
        }
    }
    
    /// <summary>
    /// 画矩形点
    /// </summary>
    /// <param name="point">坐标</param>
    /// <param name="texture">贴图</param>
    /// <param name="color">颜色</param>
    /// <param name="width">宽度</param>
    private void DrawRectDot(Vector2 point,Texture2D texture,Color color,float width){
        point.x*=texture.width;
        point.y*=texture.height;

        point.x-=width*0.5f;
        point.y-=width*0.5f;
 
        int x=Mathf.FloorToInt(point.x);
        int y=Mathf.FloorToInt(point.y);
 
        for (int i=0;i<width;i++){
            for (int j=0;j<width;j++){
                texture.SetPixel(x+i,y+j,color);
            }
        }
        texture.Apply();
    }

    /// <summary>
    /// 画圆形点
    /// </summary>
    /// <param name="point">坐标</param>
    /// <param name="texture">贴图</param>
    /// <param name="color">颜色</param>
    /// <param name="diameter">直径</param>
    private void DrawCircleDot(Vector2 point,Texture2D texture,Color color,float diameter){
        float radius=diameter*0.5f;
        
        point.x*=texture.width;
        point.y*=texture.height;

        point.x-=radius;
        point.y-=radius;
 
        int x=Mathf.FloorToInt(point.x);
        int y=Mathf.FloorToInt(point.y);
 
        for (int i=0;i<diameter;i++){
            for (int j=0;j<diameter;j++){
                float dx=i-radius;
                float dy=j-radius;
                float distance=Mathf.Sqrt(dx*dx+dy*dy);
                if(distance<=radius){
                    texture.SetPixel(x+i,y+j,color);
                }
            }
        }
        texture.Apply();
    }

}