Unity完美的UI绘画工具

直接将代码放在RawImage上（不能放在Image上面）

包含了撤销和清除功能，两个功能也可以联动

需要注意revocations变量不能等于1或者0，否则会进入死循环

用起来如果有卡顿，就改变RawImage的Scale值，Scale越大绘画越流畅

文中用到的GameManager在这篇文章：Unity学习笔记：在GameManager里记录手游操作框架_努力长头发的程序猿的博客-CSDN博客

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

public class PaintingGraffiti : MonoBehaviour,IPointerEnterHandler,IPointerExitHandler
{
    public Color color;
    //radius的值不能等于1和0,不然会进入死循环
    public int radius = 5;
    private Canvas canvas;
    private RawImage mainImage;
    private RectTransform mainRect;
    private Texture2D texture;
    private bool handIn;
    private Vector2 lastPos;
    private Color backgroundColor = Color.white;
    List> revocations = new List>();
    
    void Start()
    {
        canvas = transform.root.GetComponent();
        mainImage = GetComponent();
        mainRect = mainImage.rectTransform;
        texture = new Texture2D((int)mainRect.sizeDelta.x,(int)mainRect.sizeDelta.y);
        for (int i = 0; i < texture.width; i++)
        {
            for (int j = 0; j < texture.height; j++)
            {
                texture.SetPixel(i,j,backgroundColor);
            }
        }
        texture.Apply();
        mainImage.texture = texture;
        mainImage.SetNativeSize();
    }

    private void Update()
    {
        if(!handIn){return;}

        if (GameManager.Main.GetClick())
        {
            revocations.Insert(0,new Dictionary());
        }

        if (GameManager.Main.GetClickAlways())
        {
            Vector2 pos = GetPosForTexture();
            if (lastPos.x == 0 && lastPos.y == 0 || Vector2.Distance(pos,lastPos) <= radius/2)
            {
                DrawPoint((int)pos.x,(int)pos.y);
            }
            else
            {
                DrawLine((int)lastPos.x,(int)lastPos.y,(int)pos.x,(int)pos.y);
            }
            lastPos = pos;
        }

        if (GameManager.Main.GetClickUp())
        {
            lastPos = Vector2.zero;
        }

        if (Input.GetKeyDown(KeyCode.Z))
        {
            Revocation();
        }
        if (Input.GetKeyDown(KeyCode.C))
        {
            ClearAll();
        }
    }

    Vector2 GetPosForTexture()
    {
        Vector2 pos = Vector2.zero;
        RectTransformUtility.ScreenPointToLocalPointInRectangle
            (mainImage.rectTransform, GameManager.Main.GetNumPos(), canvas.worldCamera, out pos);
        pos.x += mainRect.sizeDelta.x * 0.5f;
        pos.y += mainRect.sizeDelta.y * 0.5f;
        return pos;
    }
    
    void DrawLine(int startX, int startY, int endX, int endY)
    {
        float k = ((float)endY - startY) / ((float)endX - startX);
        int b = startY - (int)(startX*k);
        int minX = startX < endX ? startX : endX;
        int maxX = startX > endX ? startX : endX;
        int minY = startY < endY ? startY : endY;
        int maxY = startY > endY ? startY : endY;
        if (maxY - minY > maxX - minX)
        {
            for (int i = 0; i <= maxY - minY; i+=radius/2)
            {
                if (endX == startX)
                {
                    DrawPoint(minX,minY + i);
                }
                else
                {
                    DrawPoint((int)(((minY + i) - b) / k),minY + i);
                }
            }
        }
        else
        {
            for (int i = 0; i <= maxX - minX; i+=radius/2)
            {
                DrawPoint(minX + i,b + (int)((minX + i) * k));
            }
        }
    }

    void DrawPoint(int x,int y)
    {
        int setY = 0;
        for (int i = -radius + x; i <= radius + x; i++)
        {
            setY = (radius * radius) - ((i - x) * (i - x));
            setY = (int) (Math.Sqrt(setY)) + y;
            for (int j = y - (setY - y); j <= setY; j++)
            {
                if(i<0||i>texture.width||j<0||j>texture.height){break;}
                if (texture.GetPixel(i, j) != color)
                {
                    if (!revocations[0].ContainsKey(new Vector2(i, j)))
                    {
                        revocations[0].Add(new Vector2(i,j),texture.GetPixel(i,j));
                    }
                }
                texture.SetPixel(i,j,color);
                
            }
        }
        SetTexture();
    }

    void SetTexture()
    {
        texture.Apply();
        mainImage.texture = texture;
    }

    void Revocation()
    {
        if(revocations.Count == 0){return;}
        foreach (var pos in revocations[0])
        {
            texture.SetPixel((int)pos.Key.x,(int)pos.Key.y,pos.Value);
        }
        revocations.RemoveAt(0);
        SetTexture();
    }

    void ClearAll()
    {
        revocations.Insert(0,new Dictionary());
        for (int i = 0; i <= texture.width; i++)
        {
            for (int j = 0; j <= texture.height; j++)
            {
                if (texture.GetPixel(i, j) != backgroundColor)
                {
                    revocations[0].Add(new Vector2(i,j), texture.GetPixel(i,j));
                }
                texture.SetPixel(i, j, backgroundColor);
            }
        }

        if (revocations[0].Count == 0)
        {
            revocations.RemoveAt(0);
        }

        SetTexture();
    }

    public void OnPointerEnter(PointerEventData eventData)
    {
        handIn = true;
    }

    public void OnPointerExit(PointerEventData eventData)
    {
        handIn = false;
    }

    public Texture2D GetTexture()
    {
        return texture;
    }
}