// DrawOn3D.cs

using UnityEngine;

/// <summary>
/// 在3D模型上涂鸦
/// </summary>
public class DrawOn3D : MonoBehaviour
{
    Texture2D tex;
    float[,] floats;
    int width = 1024;
    int height = 1024;
    private void Start()
    {
        MeshRenderer mr = GetComponent<MeshRenderer>();
        Material mat = mr.materials[0];
        //var texture = mat.mainTexture;

        //RenderTexture tempRT = RenderTexture.GetTemporary(texture.width, texture.height, 0, RenderTextureFormat.Default, RenderTextureReadWrite.Linear);

        //Graphics.Blit(texture, tempRT);
        //RenderTexture previous = RenderTexture.active;
        //RenderTexture.active = tempRT;

        //tex = new Texture2D(texture.width, texture.height);
        //tex.ReadPixels(new Rect(0, 0, texture.width, texture.height), 0, 0);
        //tex.Apply();

        //RenderTexture.active = previous;
        //RenderTexture.ReleaseTemporary(tempRT);

        floats = new float[width, height];
        tex = new Texture2D(width, height, TextureFormat.ARGB32, false);
        mat.SetTexture("_MaskTex", tex);
        var painColor = new Color(0, 0, 0, 0);
        for (int i = 0; i < tex.width; i++)
        {
            for (int j = 0; j < tex.height; j++)
            {
                tex.SetPixel(i, j, painColor);
            }
        }
        tex.Apply();
    }
    int R = 80;
    //默认半径
    int defaultR = 80;

    bool isDrawing = false;
    public bool isEraser = true;
    float lastTime = 0;
    Vector3 lastPos;
    Vector3 curPos;
    private void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            isDrawing = true;
            R = defaultR;
            lastTime = 0;
            lastPos = Input.mousePosition;
            curPos = Input.mousePosition;
        }
        else if (Input.GetMouseButtonUp(0))
        {
            isDrawing = false;
            R = defaultR;
            lastTime = 0;
        }
        if (isDrawing)
        {
            lastTime += Time.deltaTime;
            lastPos = Input.mousePosition;
            if (lastTime > 0.05f)
            {
                lastTime = 0;
                curPos = Input.mousePosition;
                if (Vector2.Distance(lastPos, curPos) > 1)
                {
                    R = defaultR;
                    lastPos = curPos;
                }
                else
                {
                    R += 10;
                }
                Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
                RaycastHit hit;
                if (Physics.Raycast(ray, out hit))
                {
                    Vector2 pixelUV = hit.textureCoord;
                    pixelUV.x *= tex.width;
                    pixelUV.y *= tex.height;
                    //var painColor = tex.GetPixel((int)pixelUV.x, (int)pixelUV.y);
                    //painColor.a = 0;
                    drawCircleAt((int)pixelUV.x, (int)pixelUV.y, Color.white);
                }
            }
        }
    }
    void drawCircleAt(int x, int y, Color color)
    {

        if (isEraser)
        {
            for (int i = x - R; i < x + R; i++)
            {
                if (i >= 0 && i < width)
                {
                    for (int j = y - R; j < y + R; j++)
                    {
                        if (j >= 0 && j < height && floats[i, j] >= 0)
                        {
                            float distance = Vector2.Distance(new Vector2(i, j), new Vector2(x, y));
                            if (distance <= R)
                            {
                                floats[i, j] -= 1 - distance / R;
                                tex.SetPixel(i, j, color * (1 - floats[i, j]));
                            }
                        }
                    }
                }
            }
        }
        else
        {
            for (int i = x - R; i < x + R; i++)
            {
                if (i >= 0 && i < width)
                {
                    for (int j = y - R; j < y + R; j++)
                    {
                        if (j >= 0 && j < height && floats[i, j] <= 1)
                        {
                            float distance = Vector2.Distance(new Vector2(i, j), new Vector2(x, y));
                            if (distance <= R)
                            {
                                floats[i, j] += 1 - distance / R;
                                tex.SetPixel(i, j, color * (1 - floats[i, j]));
                            }
                        }
                    }
                }
            }
        }
        tex.Apply();
    }
}