unity 高斯模糊 shader

Shader "Custom/BackBlur"
{
    Properties
    {
        _MainTex("Sprite Texture", 2D) = "white" {}
        _Color("Main Color", Color) = (1,1,1,1)
        _Size("Size", Range(0, 20)) = 1
    }
        SubShader
        {
            Tags { "Queue" = "Transparent" "IgnoreProjector" = "True" "RenderType" = "Transparent" "PreviewType" = "Plane" "CanUseSpriteAtlas" = "True" }
            LOD 200
            ZWrite Off
            Blend SrcAlpha OneMinusSrcAlpha

            // Horizontal blur  
            GrabPass {}
            Pass
            {
                Tags { "LightMode" = "Always" }
                Name "BackBlurHor"
                CGPROGRAM
                #pragma vertex vert  
                #pragma fragment frag  
                #pragma fragmentoption ARB_precision_hint_fastest  
                #include "UnityCG.cginc"  

                struct appdata_t
                {
                    float4 vertex : POSITION;
                    float2 texcoord : TEXCOORD0;
                    float4 color : COLOR;
                };

                struct v2f
                {
                    float4 vertex : POSITION;
                    float4 uvgrab : TEXCOORD0;
                    float4 color : COLOR;
                };

                v2f vert(appdata_t v)
                {
                    v2f o;
                    o.vertex = UnityObjectToClipPos(v.vertex);
                    #if UNITY_UV_STARTS_AT_TOP  
                    float scale = -1.0;
                    #else  
                    float scale = 1.0;
                    #endif  
                    o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y * scale) + o.vertex.w) * 0.5;
                    o.uvgrab.zw = o.vertex.zw;
                    o.color = v.color;
                    return o;
                }

                sampler2D _GrabTexture;
                float4 _GrabTexture_TexelSize;
                float _Size;
                uniform float4 _Color;

                half4 GrabPixel(v2f i, float weight, float kernelx)
                {
                    if (i.uvgrab.x == 0 && i.uvgrab.y == 0)
                        kernelx = 0;
                    return tex2Dproj(_GrabTexture, UNITY_PROJ_COORD(float4(i.uvgrab.x + _GrabTexture_TexelSize.x * kernelx * _Size, i.uvgrab.y, i.uvgrab.z, i.uvgrab.w))) * weight;
                }

                half4 frag(v2f i) : COLOR
                {
                    half4 sum = half4(0,0,0,0);
                    sum += GrabPixel(i, 0.05, -4.0);
                    sum += GrabPixel(i, 0.09, -3.0);
                    sum += GrabPixel(i, 0.12, -2.0);
                    sum += GrabPixel(i, 0.15, -1.0);
                    sum += GrabPixel(i, 0.18, 0.0);
                    sum += GrabPixel(i, 0.15, +1.0);
                    sum += GrabPixel(i, 0.12, +2.0);
                    sum += GrabPixel(i, 0.09, +3.0);
                    sum += GrabPixel(i, 0.05, +4.0);

                    float4 col5 = tex2Dproj(_GrabTexture, UNITY_PROJ_COORD(i.uvgrab));
                    float decayFactor = 1.0f;
                    sum = lerp(col5, sum, decayFactor) * i.color * _Color;

                    return sum;
                }
                ENDCG
            }

            // Vertical blur  
            GrabPass {}
            Pass
            {
                Tags { "LightMode" = "Always" }
                Name "BackBlurVer"
                CGPROGRAM
                #pragma vertex vert  
                #pragma fragment frag  
                #pragma fragmentoption ARB_precision_hint_fastest  
                #include "UnityCG.cginc"  

                struct appdata_t
                {
                    float4 vertex : POSITION;
                    float2 texcoord : TEXCOORD0;
                    float4 color : COLOR;
                };

                struct v2f
                {
                    float4 vertex : POSITION;
                    float4 uvgrab : TEXCOORD0;
                    float4 color : COLOR;
                };

                v2f vert(appdata_t v)
                {
                    v2f o;
                    o.vertex = UnityObjectToClipPos(v.vertex);
                    #if UNITY_UV_STARTS_AT_TOP  
                    float scale = -1.0;
                    #else  
                    float scale = 1.0;
                    #endif  
                    o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y * scale) + o.vertex.w) * 0.5;
                    o.uvgrab.zw = o.vertex.zw;
                    o.color = v.color;
                    return o;
                }

                sampler2D _GrabTexture;
                float4 _GrabTexture_TexelSize;
                float _Size;
                uniform float4 _Color;

                half4 GrabPixel(v2f i, float weight, float kernely)
                {
                    if (i.uvgrab.x == 0 && i.uvgrab.y == 0)
                        kernely = 0;
                    return tex2Dproj(_GrabTexture, UNITY_PROJ_COORD(float4(i.uvgrab.x, i.uvgrab.y + _GrabTexture_TexelSize.y * kernely * _Size, i.uvgrab.z, i.uvgrab.w))) * weight;
                }

                half4 frag(v2f i) : COLOR
                {
                    half4 sum = half4(0,0,0,0);
                    sum += GrabPixel(i, 0.05, -4.0);
                    sum += GrabPixel(i, 0.09, -3.0);
                    sum += GrabPixel(i, 0.12, -2.0);
                    sum += GrabPixel(i, 0.15, -1.0);
                    sum += GrabPixel(i, 0.18, 0.0);
                    sum += GrabPixel(i, 0.15, +1.0);
                    sum += GrabPixel(i, 0.12, +2.0);
                    sum += GrabPixel(i, 0.09, +3.0);
                    sum += GrabPixel(i, 0.05, +4.0);

                    float4 col5 = tex2Dproj(_GrabTexture, UNITY_PROJ_COORD(i.uvgrab));
                    float decayFactor = 1.0f;
                    sum = lerp(col5, sum, decayFactor) * i.color * _Color;

                    return sum;
                }
                ENDCG
            }
        }
            FallBack "Diffuse"
}