using UnityEngine;
using UnityEngine.UI;

public class UIBgBlur : MonoBehaviour
{
    // 高斯模糊迭代次数
    [Range(0, 6)]
    public int Iterations = 5;
    // 每次迭代纹理坐标偏移的速度
    [Range(0.2f, 4.0f)]
    public float BlurSpread = 3f;
    // 降采样比率 
    [Range(1, 8)]
    public int DownSample = 4;
    private RawImage _blurImage;
    private RenderTexture _srcTexture, _destTexture;
    private Texture2D _texture2D;
    private Material _material;
    private void Awake()
    {
        _blurImage = transform.GetComponent<RawImage>();
        _material = _blurImage.material;
        _blurImage.material = null;

        _srcTexture = new RenderTexture(Screen.width, Screen.height, 24, RenderTextureFormat.ARGB32);
        _destTexture = new RenderTexture(Screen.width, Screen.height, 24, RenderTextureFormat.ARGB32);

        SetEnanble(true);
    }

    public void SetSortingOrder(int order)
    {
        Canvas blurCanvas = GetComponent<Canvas>();
        blurCanvas.overrideSorting = true;
        blurCanvas.sortingOrder = order;
    }

    public void SetEnanble(bool isOK)
    {
        Camera camera = Camera.main;
        _blurImage.gameObject.SetActive(isOK && camera != null);
        if (isOK)
            DrawCameraBlur(camera);
    }

    /// <summary>
    /// 绘制相机的图片
    /// </summary> 
    private void DrawCameraBlur(Camera camera)
    {

        if (camera == null)
            return;
        //保存相机渲染用于后面恢复
        var cameraPrevT = camera.targetTexture;
        camera.targetTexture = _srcTexture;
        camera.Render();
        // 还原相机渲染目标
        camera.targetTexture = cameraPrevT;
        OnRender(_srcTexture, _destTexture);
        // 设置当前活动的渲染纹理
        RenderTexture.active = _destTexture;
        //创建一个Texture2D
        if (_texture2D == null)
            _texture2D = new Texture2D(_destTexture.width, _destTexture.height, TextureFormat.RGB24, false);
        var texRect = new Rect(0, 0, _destTexture.width, _destTexture.height);
        _texture2D.ReadPixels(texRect, 0, 0);
        _texture2D.Apply();
        // 清空
        RenderTexture.active = null;
        // 赋值给RawImage
        _blurImage.texture = _texture2D;
    }

    /// <summary>
    /// 用Shader渲染高斯模糊
    /// </summary> 
    private void OnRender(RenderTexture src, RenderTexture dest)
    {
        if (_material != null)
        {
            // 降采样的纹理宽度
            int rtW = src.width / DownSample;
            // 降采样的纹理高度
            int rtH = src.height / DownSample;
            RenderTexture buffer0 = RenderTexture.GetTemporary(rtW, rtH, 0);
            // 滤波模式设置为双线性
            buffer0.filterMode = FilterMode.Bilinear;
            Graphics.Blit(src, buffer0);
            for (int i = 0; i < Iterations; i++)
            {
                // 设置模糊尺寸(纹理坐标的偏移量)
                _material.SetFloat("_BlurSize", 1.0f + i * BlurSpread);
                RenderTexture buffer1 = RenderTexture.GetTemporary(rtW, rtH, 0);
                // 渲染垂直的Pass
                Graphics.Blit(buffer0, buffer1, _material, 0);
                RenderTexture.ReleaseTemporary(buffer0);
                buffer0 = buffer1;
                buffer1 = RenderTexture.GetTemporary(rtW, rtH, 0);
                // 渲染水平的Pass
                Graphics.Blit(buffer0, buffer1, _material, 1);
                RenderTexture.ReleaseTemporary(buffer0);
                buffer0 = buffer1;
            }
            Graphics.Blit(buffer0, dest);
            RenderTexture.ReleaseTemporary(buffer0);
        }
        else
        {
            Graphics.Blit(src, dest);
        }
    }
}

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

Shader "MyShader/GaussianBlur" { // 高斯模糊
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {} // 主纹理
        _BlurSize ("Blur Size", Float) = 1.0 // 模糊尺寸(纹理坐标的偏移量)
    }
 
    SubShader {
        CGINCLUDE
        
        #include "UnityCG.cginc"
        
        sampler2D _MainTex; // 主纹理
        half4 _MainTex_TexelSize; // _MainTex的像素尺寸大小, float4(1/width, 1/height, width, height)
        float _BlurSize; // 模糊尺寸(纹理坐标的偏移量)
          
        struct v2f {
            float4 pos : SV_POSITION; // 模型空间顶点坐标
            half2 uv[5]: TEXCOORD0; // 5个邻域的纹理坐标
        };
          
        v2f vertBlurVertical(appdata_img v) { // 垂直模糊顶点着色器
            v2f o;
            o.pos = UnityObjectToClipPos(v.vertex); // 模型空间顶点坐标变换到裁剪空间, 等价于: mul(UNITY_MATRIX_MVP, v.vertex)
            half2 uv = v.texcoord;
            o.uv[0] = uv;
            o.uv[1] = uv + float2(0.0, _MainTex_TexelSize.y * 1.0) * _BlurSize;
            o.uv[2] = uv - float2(0.0, _MainTex_TexelSize.y * 1.0) * _BlurSize;
            o.uv[3] = uv + float2(0.0, _MainTex_TexelSize.y * 2.0) * _BlurSize;
            o.uv[4] = uv - float2(0.0, _MainTex_TexelSize.y * 2.0) * _BlurSize;      
            return o;
        }
        
        v2f vertBlurHorizontal(appdata_img v) { // 水平模糊顶点着色器
            v2f o;
            o.pos = UnityObjectToClipPos(v.vertex); // 模型空间顶点坐标变换到裁剪空间, 等价于: mul(UNITY_MATRIX_MVP, v.vertex)
            half2 uv = v.texcoord;
            o.uv[0] = uv;
            o.uv[1] = uv + float2(_MainTex_TexelSize.x * 1.0, 0.0) * _BlurSize;
            o.uv[2] = uv - float2(_MainTex_TexelSize.x * 1.0, 0.0) * _BlurSize;
            o.uv[3] = uv + float2(_MainTex_TexelSize.x * 2.0, 0.0) * _BlurSize;
            o.uv[4] = uv - float2(_MainTex_TexelSize.x * 2.0, 0.0) * _BlurSize;      
            return o;
        }
 
        fixed4 fragBlur(v2f i) : SV_Target {
            float weight[3] = {0.4026, 0.2442, 0.0545}; // 大小为5的一维高斯核，实际只需记录3个权值
            fixed3 sum = tex2D(_MainTex, i.uv[0]).rgb * weight[0];
            for (int j = 1; j < 3; j++) {
                sum += tex2D(_MainTex, i.uv[j * 2 - 1]).rgb * weight[j]; // 中心右侧或下侧的纹理*权值
                sum += tex2D(_MainTex, i.uv[j * 2]).rgb * weight[j]; // 中心左侧或上侧的纹理*权值
            }
            return fixed4(sum, 1.0);
        }
            
        ENDCG
        
        ZTest Always Cull Off ZWrite Off
        
        Pass {
            NAME "GAUSSIAN_BLUR_VERTICAL"
            
            CGPROGRAM
              
            #pragma vertex vertBlurVertical  
            #pragma fragment fragBlur
              
            ENDCG  
        }
        
        Pass {  
            NAME "GAUSSIAN_BLUR_HORIZONTAL"
            
            CGPROGRAM  
            
            #pragma vertex vertBlurHorizontal  
            #pragma fragment fragBlur
            
            ENDCG
        }
    }
 
    FallBack "Diffuse"
}