Introduction to graphics: graphic painting (I)

       Recently, I want to realize a series of painting functions , I think it's very useful .
       The first is ordinary color rendering , Use material texture to paint , as follows ：

       Suppose there is a texture on it uv, Our mouse rays hit muv, according to radius Calculate the drawn circumscribed rectangle rect, Then judge the circle coloring according to the distance from the arc to the center of the circle . The only thing to pay attention to here is the boundary of texture pixels , Don't cross the line , as follows ：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class TestColorSpray : MonoBehaviour
{
    
    public Color color;         // Color 
    [Range(0, 1)]
    public float alpha;         // transparency 
    public int radius;          // Radius pixels 

    private Camera cam;

    private bool isStart = false;

    private Material mat;
    private Texture2D tex;
    private int texWidth;
    private int texHeight;

    void Start()
    {
    
        cam = Camera.main;
    }

    void FixedUpdate()
    {
    
        if (Input.GetMouseButtonDown(0))
        {
    
            Ray ray = cam.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;
            if (Physics.Raycast(ray, out hit))
            {
    
                StartSpray(hit.transform);
            }
        }
        if (Input.GetMouseButton(0))
        {
    
            if (isStart)
            {
    
                Ray ray = cam.ScreenPointToRay(Input.mousePosition);
                RaycastHit hit;
                if (Physics.Raycast(ray, out hit))
                {
    
#if UNITY_EDITOR
                    Debug.DrawLine(cam.transform.position, hit.point, Color.black);
#endif
                    // Mouse Center 
                    Vector2 muv = new Vector2(hit.textureCoord.x * texWidth, hit.textureCoord.y * texHeight);
                    int mx = Mathf.Clamp((int)muv.x, 0, texWidth - 1);
                    int my = Mathf.Clamp((int)muv.y, 0, texHeight - 1);
                    // Outside rectangle （ Irregular ）
                    int left = Mathf.Clamp(mx - radius, 0, texWidth - 1);
                    int right = Mathf.Clamp(mx + radius, 0, texWidth - 1);
                    int bottom = Mathf.Clamp(my - radius, 0, texHeight - 1);
                    int top = Mathf.Clamp(my + radius, 0, texHeight - 1);
                    int rectwid = right - left;
                    int recthei = top - bottom;
                    // draw 
                    Color[] ogcols = tex.GetPixels(left, bottom, rectwid, recthei);
                    // progressive scanning 
                    for (int y = 0; y < recthei; y++)
                    {
    
                        for (int x = 0; x < rectwid; x++)
                        {
    
                            int index = y * rectwid + x;
                            int px = x + left - mx;
                            int py = y + bottom - my;
                            float alphainten;
                            if (CheckInCircle(radius, px, py, out alphainten))
                            {
    
                                Color ocol = ogcols[index];
                                Color scol = color;
                                float inten = alphainten * alpha;
                                ogcols[index] = BlendColor(ocol, scol, inten);
                            }
                        }
                    }
                    tex.SetPixels(left, bottom, rectwid, recthei, ogcols);
                    tex.Apply();
                }
            }
        }
        if (Input.GetMouseButtonUp(0))
        {
    
            StopSpray();
        }
    }

    private void StartSpray(Transform obj)
    {
    
        isStart = true;
        mat = obj.GetComponent<MeshRenderer>().sharedMaterial;
        tex = (Texture2D)mat.GetTexture("_MainTex");
        texWidth = tex.width;
        texHeight = tex.height;
    }

    private void StopSpray()
    {
    
        isStart = false;
    }

    /// <summary>
    ///  testing xy stay rad Circular middle 
    ///  Relative coordinates , center of a circle (0,0)
    /// </summary>
    /// <param name="rad"></param>
    /// <param name="x"></param>
    /// <param name="y"></param>
    /// <param name="inten"></param>
    /// <returns></returns>
    private bool CheckInCircle(int rad, int x, int y, out float inten)
    {
    
        float rad2 = rad * rad;
        float len2 = x * x + y * y;
        inten = 1f - len2 / rad2;
        return len2 <= rad2;
    }
    /// <summary>
    ///  Mix colors 
    /// </summary>
    /// <param name="a"></param>
    /// <param name="b"></param>
    /// <returns></returns>
    private Color BlendColor(Color a, Color b, float k)
    {
    
        Color c = Color.Lerp(a, b, k);
        return c;
    }
}

       Test it ,material Of maintex Set to readwrite/rgba32, as follows ：

       But there's a small problem , It is suggested to make a copy of the material picture , Otherwise Apply Covering the original data , as follows ：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SprayObject : MonoBehaviour
{
    
    void Start()
    {
    
        MeshRenderer render = gameObject.GetComponent<MeshRenderer>();
        Material mat = render.material;
        Texture2D tex = (Texture2D)mat.GetTexture("_MainTex");
        Texture2D copytex = new Texture2D(tex.width, tex.height, tex.format, false);
        copytex.SetPixels(tex.GetPixels());
        copytex.Apply();
        mat.SetTexture("_MainTex", copytex);
    }
}

       In this way, the objects we spray on first clone A material and map .
       At the same time, there is a big problem in this scheme , That's it uv Joints cannot be treated , as follows ：

       Because of the uv Is discontinuous and random （ According to the artists uvmapping） Of , Therefore, the continuity of spraying cannot be handled , If it's true , We have to think of another spraying scheme .
       Of course, the current plan also has a certain place to play , For example, brush the terrain 、 Brush objects , I use this .
       There are also brush patterns and textures , as follows ：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class TestGraphSpray : MonoBehaviour
{
    
    public Texture2D graphTex;  // pattern 
    [Range(0, 1)]
    public float alpha;         // transparency 

    private Camera cam;

    private bool isStart = false;

    private Material mat;
    private Texture2D tex;
    private int texWidth;
    private int texHeight;

    private int gWid;           // The pattern is wide 
    private int gHei;           // The pattern is high 
    private int ghWid;          // Pattern half width 
    private int ghHei;          // The pattern is half height 

    void Start()
    {
    
        cam = Camera.main;

        gWid = graphTex.width;
        gHei = graphTex.height;
        ghWid = (int)(gWid * 0.5f);
        ghHei = (int)(graphTex.height * 0.5f);
    }

    void Update()
    {
    
        if (Input.GetMouseButtonDown(0))
        {
    
            Ray ray = cam.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;
            if (Physics.Raycast(ray, out hit))
            {
    
                StartSpray(hit.transform);
            }
        }
        if (Input.GetMouseButton(0))
        {
    
            if (isStart)
            {
    
                Ray ray = cam.ScreenPointToRay(Input.mousePosition);
                RaycastHit hit;
                if (Physics.Raycast(ray, out hit))
                {
    
#if UNITY_EDITOR
                    Debug.DrawLine(cam.transform.position, hit.point, Color.black);
#endif
                    // Mouse Center 
                    Vector2 muv = new Vector2(hit.textureCoord.x * texWidth, hit.textureCoord.y * texHeight);
                    int mx = Mathf.Clamp((int)muv.x, 0, texWidth - 1);
                    int my = Mathf.Clamp((int)muv.y, 0, texHeight - 1);
                    // Outside rectangle （ Irregular ）
                    int left = Mathf.Clamp(mx - ghWid, 0, texWidth - 1);
                    int right = Mathf.Clamp(mx + ghWid, 0, texWidth - 1);
                    int bottom = Mathf.Clamp(my - ghHei, 0, texHeight - 1);
                    int top = Mathf.Clamp(my + ghHei, 0, texHeight - 1);
                    int rectwid = right - left;
                    int recthei = top - bottom;
                    // draw 
                    Color[] ocols = tex.GetPixels(left, bottom, rectwid, recthei);
                    // According to whether the rectangle is out of bounds , Judge graphTex Starting point of sampling 
                    int gx = mx > ghWid ? 0 : ghWid - mx;
                    int gy = my > ghHei ? 0 : ghHei - my;
                    Color[] gcols = graphTex.GetPixels(gx, gy, rectwid, recthei);
                    // progressive scanning 
                    for (int y = 0; y < recthei; y++)
                    {
    
                        for (int x = 0; x < rectwid; x++)
                        {
    
                            int index = y * rectwid + x;
                            Color ocol = ocols[index];
                            Color gcol = gcols[index];
                            float k = alpha * gcol.a;
                            ocols[index] = BlendColor(ocol, gcol, k);
                        }
                    }
                    tex.SetPixels(left, bottom, rectwid, recthei, ocols);
                    tex.Apply();
                }
            }
        }
        if (Input.GetMouseButtonUp(0))
        {
    
            StopSpray();
        }
    }

    private void StartSpray(Transform obj)
    {
    
        isStart = true;
        mat = obj.GetComponent<MeshRenderer>().sharedMaterial;
        tex = (Texture2D)mat.GetTexture("_MainTex");
        texWidth = tex.width;
        texHeight = tex.height;
    }

    private void StopSpray()
    {
    
        isStart = false;
    }

    private Color BlendColor(Color a, Color b, float k)
    {
    
        Color c = Color.Lerp(a, b, k);
        return c;
    }
}

       The core is based on drawing rect Just mix the sampling pattern with the background color array , The effect is as follows ：
       Pay special attention to rectangles “ breakthrough ” The problem of pattern sampling coordinates in the case of boundary .
       Of course, there are still many problems that need to be solved , such as ：
      1. Model UV joint 、 How to deal with the joint spraying between models ？
      2. spraying + Grid computing works together , similar zbrush operation ？
      3. Can we handle it? 3d Texture matching model coloring ？
       Later, there is time to slowly realize .
       by the way , By the way , This kind of drawing operation is not suitable for use ComputeShader, I wrote a test , although ComputeShader In the calculation of color matrix CPU fast , But on the data bus bus The exchange is too time-consuming , Not suitable for this spraying operation .