Unity 中实现擦除功能

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通过一个小Trick实现shader的像素识别/统计操

1.简介

将一张大图分成多个小块逐步处理并逐步合并，保留关键像素的向下采样：

但我在思考一种更简便的方法，于是想到在顶点shader里做判断检测，在像素shader里获取结果这样一个形式：

用一组顶点去读单个像素，判断失败的顶点坐标提交到屏幕外，而判断成功的顶点坐标放在屏幕内。

最后在CPU中获取是否有屏幕内顶点这样一个结果，来进行简单的识别操作。

而在开启透明之后，还可以用透明度叠加来获取更复杂的结果。

2.实践

首先实践结果并没有想象的那么好，因为如果纯用三角面来做顶点部分的判断未免太费效率了。

所以我改成了传入顶点判断并生成面的方式，并且缩小了传入图片的像素大小。

Graphics.DrawProcedural(MeshTopology.Points, blueTex.width * blueTex.height, 1);

毕竟更多的运用场合是用来做刮刮卡或者擦除的识别。只需要检测mask图片。

上代码：

Shader "Hidden/FooShader"
{
    Properties
    {
    }
    SubShader
    {
        Blend One One

        tags
        {
            "Queue" = "Transparent"
            "RenderType" = "Transparent"
        }

        Pass
        {
            CGPROGRAM
            #pragma target 4.0
            #pragma vertex vert
            #pragma geometry geom
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct v2f
            {
                float4 color : COLOR;
                float4 vertex : SV_POSITION;
            };

            sampler2D _Image;
            float4 _ImageSize;

            v2f vert(uint vid : SV_VertexID)
            {
                v2f o = (v2f)0;

                half y = floor(vid / _ImageSize.x);
                half x = (vid - y * _ImageSize.x) / _ImageSize.x;
                y = y / _ImageSize.y;

                o.vertex = 0;

                float4 image_col = tex2Dlod(_Image, half4(x,y,0,0));

                if (all(image_col.rgb == half3(0, 0, 1)))
                //if (all(image_col.rgb == half3(0, 1, 1)))    /*error*/
                {
                    o.color = 1;
                }
                else
                {
                    o.color = 0;
                }

                return o;
            }

            [maxvertexcount(4)]
            void geom(point v2f vertElement[1], inout TriangleStream<v2f> triStream)
            {
                if (vertElement[0].color.r <= 0) return;

                float size = 10;

                float4 v1 = vertElement[0].vertex + float4(-size, -size, 0, 0);
                float4 v2 = vertElement[0].vertex + float4(-size, size, 0, 0);
                float4 v3 = vertElement[0].vertex + float4(size, -size, 0, 0);
                float4 v4 = vertElement[0].vertex + float4(size, size, 0, 0);

                v2f r = (v2f)0;

                r.vertex = mul(UNITY_MATRIX_VP, v1);
                r.color = vertElement[0].color;
                triStream.Append(r);

                r.vertex = mul(UNITY_MATRIX_VP, v2);
                r.color = vertElement[0].color;
                triStream.Append(r);

                r.vertex = mul(UNITY_MATRIX_VP, v3);
                r.color = vertElement[0].color;
                triStream.Append(r);

                r.vertex = mul(UNITY_MATRIX_VP, v4);
                r.color = vertElement[0].color;
                triStream.Append(r);
            }

            fixed4 frag(v2f i) : SV_Target
            {
                return i.color;
            }
            ENDCG
        }
    }
}

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

namespace Hont
{
    public class Foo : MonoBehaviour
    {
        void Start()
        {
            var blueTex = new Texture2D(64, 64);
            for (int x = 0; x < blueTex.width; x++)
                for (int y = 0; y < blueTex.height; y++)
                    blueTex.SetPixel(x, y, Color.blue);
            blueTex.Apply();

            var mat = new Material(Shader.Find("Hidden/FooShader"));
            mat.SetTexture("_Image", blueTex);
            mat.SetVector("_ImageSize", new Vector4(blueTex.width, blueTex.height));
            mat.SetPass(0);
            var tempRT = RenderTexture.GetTemporary(16, 16, 0, RenderTextureFormat.ARGB32, RenderTextureReadWrite.sRGB, 1);
            tempRT.filterMode = FilterMode.Point;
            tempRT.autoGenerateMips = false;
            tempRT.anisoLevel = 0;
            tempRT.wrapMode = TextureWrapMode.Clamp;
            var cacheRT = RenderTexture.active;
            RenderTexture.active = tempRT;
            Graphics.DrawProcedural(MeshTopology.Points, blueTex.width * blueTex.height, 1);
            var tex2D = new Texture2D(16, 16, TextureFormat.ARGB32, false, false);
            tex2D.wrapMode = TextureWrapMode.Clamp;
            tex2D.anisoLevel = 0;
            tex2D.filterMode = FilterMode.Point;
            tex2D.ReadPixels(new Rect(0, 0, 16, 16), 0, 0);
            var firstPixel = tex2D.GetPixel(0, 0);
            Debug.Log("firstPixel: " + firstPixel);
            RenderTexture.active = cacheRT;
            RenderTexture.ReleaseTemporary(tempRT);
        }
    }
}

跑了一下代码之后我发现了三个问题，也是没解决的问题，一个是计算结果有误差

o.color = float4(0.05, 0, 0, 0);

输出是0.05结果却有一些出入。

特别是当返回颜色小于0.1之后，我尝试改变图像格式或者RT等参数依旧没能解决

第二个问题是开启透明后，透明图片的叠加是有上限的，毕竟深度有限，堆叠二十多层后，后面层会丢失。

第三个问题是传入图片尺寸过大直接导致带宽爆炸，以至于unity直接假死了，512x512的图片就是26万多的像素要处理，也就是26万多的顶点。

第三个问题很好解决，控制图片尺寸+让单个顶点采样更多像素即可。

对于第一个问题，目前还不需要太精确所以没解决但也能用。第二个问题可以用一些方法来缓解

比如在顶点shader中增加运算量，把返回值分散到rgba四个通道上去。

uint roll = (roll_width + roll_height) % 4;

if (roll == 0)
    result = float4(GAIN_VALUE, 0, 0, 0);

if (roll == 1)
    result = float4(0, GAIN_VALUE, 0, 0);

if (roll == 2)
    result = float4(0, 0, GAIN_VALUE, 0);

if (roll == 3)
    result = float4(0, 0, 0, GAIN_VALUE);

把更多的像素遍历放入顶点中，这样处理图片的顶点数量是原大小/n:

v2f vert(uint vid : SV_VertexID)
{
    v2f o = (v2f)0;

    o.vertex = 0;

    half2 image_size = half2(GRID_SIZE_X * LOOP_IMAGE_SIZE_X, GRID_SIZE_Y * LOOP_IMAGE_SIZE_Y);

    half y = floor(vid / LOOP_IMAGE_SIZE_X);
    half x = (vid - y * LOOP_IMAGE_SIZE_X) / LOOP_IMAGE_SIZE_X;
    y = y / LOOP_IMAGE_SIZE_Y;
    //将vid转化为x,y坐标

    for (half rx = 0; rx < GRID_SIZE_X; rx++)
    {
        for (half ry = 0; ry < GRID_SIZE_Y; ry++)
        {
            half xx = x + rx;
            half yy = y + ry;

            float4 r = Statistics_sample(_Image, _Rec_Color, half4(xx, yy, 0, 0), image_size);

            o.color += r;
        }
    }
    //一个顶点处理多个像素

    return o;
}

3.测试结果

最终达到了一个比较不错的结果，我把相关函数封装成了一个类。

我写了一个涂抹效果demo来测试一下，它通过识别白色像素的数量来判断是否为全部涂完：

工程文件我丢在了github上: https://github.com/hont127/Image-Rec-Base-unity-shader-

GUGI 中通过改变像素实现擦除

这种方法需要改精灵的设置，如下：

话不多说，直接上代码：

using System.Collections.Generic;
using System.Reflection.Emit;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.Profiling;
using UnityEngine.UI;


public class ChangeTexturePixel : MonoBehaviour, IDragHandler
{
    /// <summary> 擦除的像素数量 </summary>
    private int m_PixelAcount = 0;
    
    /// <summary> 是否擦除成功 </summary>
    private bool m_IsDrag = false;
    
    /// <summary> 擦除范围大小 </summary>
    [SerializeField][Range(10,100)]
    private int Radius = 10;
    
    /// <summary> 擦除完成度（不超过1）</summary>
    [SerializeField][Range(0,1)] 
    private float m_Complete; 
    
    private RawImage m_UITex;
    
    private Texture2D m_MyTex;

    [SerializeField]
    private Color m_Col = Color.clear;
    
    private int[][] m_PixelArray;
  
    private Dictionary<int, TexturePixel> m_TexPixelDic = new Dictionary<int, TexturePixel>();

    void Start()
    {
        m_IsDrag = false;
        m_UITex = GetComponent<RawImage>();
        var tex = m_UITex.texture as Texture2D;

        m_MyTex = new Texture2D(tex.width, tex.height, TextureFormat.ARGB32,
            false); 

        m_MyTex.SetPixels(tex.GetPixels());
        m_MyTex.Apply();
        m_UITex.texture = m_MyTex;
        
        int value = 0;
        m_PixelArray = new int[m_MyTex.width][];
        for (int i = 0; i < m_PixelArray.Length; i++)
        {
            m_PixelArray[i] = new int[m_MyTex.height];
            for (int j = 0; j < m_MyTex.height; j++)
            {
                m_PixelArray[i][j] = value;

                m_TexPixelDic.Add(value, new TexturePixel(m_MyTex, i, j));
                value++;
            }
        }
        
    }

    /// <summary>
    ///  改变Texture2D像素点颜色
    /// </summary>
    /// <param name="x">Texture2D像素点X轴位置</param>
    /// <param name="y">Texture2D像素点Y轴位置</param>
    /// <param name="radius">改变像素的范围</param>
    /// <param name="col">改变后的颜色</param>
    void ChangePixelColorByCircle(int x, int y, int radius, Color col)
    {
        for (int i = -Radius; i < Radius; i++)
        {
            var py = y + i;
            if (py < 0 || py >= m_MyTex.height)
            {
                continue;
            }

            for (int j = -Radius; j < Radius; j++)
            {
                var px = x + j;
                if (px < 0 || px >= m_MyTex.width)
                {
                    continue;
                }

                if (new Vector2(px - x, py - y).magnitude > Radius)
                {
                    continue;
                }

                Profiler.BeginSample("text1");
                TexturePixel tp; //= texPixelDic[pixelArray[MyTex.width - 1][py]];

                if (px == 0)
                {
                    tp = m_TexPixelDic[m_PixelArray[m_MyTex.width - 1][py]];
                    tp.Scratch(m_Col);
                  
                }
                
                tp = m_TexPixelDic[m_PixelArray[px][py]];
                if (!tp.GetPixel())
                {
                    m_PixelAcount++;
                }
                tp.Scratch(m_Col);
                
                Profiler.EndSample();
            }
        }

        Profiler.BeginSample("text2");
        m_MyTex.Apply();
        Profiler.EndSample();
        Profiler.BeginSample("text3");
        Profiler.EndSample();
    }

     /// <summary>
     ///  擦除点
     /// </summary>
     /// <param name="mousePos">鼠标位置</param>
     /// <returns>擦除点</returns>
    Vector2 ScreenPoint2Pixel(Vector2 mousePos)
    {
        float imageWidth = m_UITex.rectTransform.sizeDelta.x;
        float imageHeight = m_UITex.rectTransform.sizeDelta.y;
        Vector3 imagePos = m_UITex.rectTransform.anchoredPosition3D;
        //求鼠标在image上的位置
        float HorizontalPercent =
            (mousePos.x - (Screen.width / 2 + imagePos.x - imageWidth / 2)) / imageWidth; //鼠标在Image 水平上的位置  %
        float verticalPercent =
            (mousePos.y - (Screen.height / 2 + imagePos.y - imageHeight / 2)) / imageHeight; //鼠标在Image 垂直上的位置  %
        float x = HorizontalPercent * m_MyTex.width;
        float y = verticalPercent * m_MyTex.height;
        return new Vector2(x, y);
    }

    
    /// <summary>
    ///  拖拽中。。。
    /// </summary>
    /// <param name="eventData">拖拽数据</param>
    public void OnDrag(PointerEventData eventData)
    {
        if (!m_IsDrag)
        {
            var posA = ScreenPoint2Pixel(eventData.position);
            ChangePixelColorByCircle((int) posA.x, (int) posA.y, Radius, m_Col);
            SetAllPixelFadeAlpha();

        }
    }

    /// <summary>
    ///  擦除完成时调用
    /// </summary>
    public void SetAllPixelFadeAlpha()
    {
        if (++m_PixelAcount >= m_MyTex.height*m_MyTex.width*m_Complete)
        {  
            m_UITex.color = Color.clear;
            m_IsDrag = true;
            Debug.Log("擦除完成");
        }
    }
}

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

public class TexturePixel
{
    public Texture2D myTex;
    //float alpha = 1;        //当前透明度
   // int scratchedTime = 0;//被刮的次数
    private int x;      //像素坐标X
    private int y;      //像素坐标Y
    //private bool scratcedPrevious = false;
    //private bool scratcedCurrent = false;
    public TexturePixel(Texture2D tex,int x,int y)
    {
        myTex = tex;
        this.x = x;
        this.y = y;
    }

    public void Scratch( Color targetCol)
    {
        myTex.SetPixel(x,y,targetCol);
      //  scratcedCurrent = true;
        //Debug.Log("x:"+x+"  y:"+y+"  a "+ targetCol.a);
    }

    public bool GetPixel()
    {
      Color color =  myTex.GetPixel(x, y);
      
      return color.a <= 0;
    }

以上方法是通过改变Texture2D像素点颜色实现擦除，主要内容：

// 设置像素点
 myTex.SetPixel(x,y,targetCol);
// 获取像素点
 myTex.GetPixel(x,y,targetCol);

项目文件我放在了gitee: https://gitee.com/ondaly/eraser_-master.git
项目案例查看。