unity 高斯模糊shader

闲着没事，写了个高斯模糊的shader，有用的到的可以mark

Shader "Unlit/GaussionBlur"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        //值越大，正态分布图像越扁，距离远的像素的权重越高，颗粒感越明显
        _Sigma("Sigma", Range(1, 30)) = 20
        //多少倍的Sigma，值越大，采样越多，越细腻，会循环(2n+1)(2n+1)次，所以这个值不要太大，太大也没用
		_Ratio("Sigma Ratio", Range(1, 4)) = 2
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // make fog work
            #pragma multi_compile_fog

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float4 _MainTex_TexelSize;

            float _Sigma;
            float _Ratio;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
				float sum=0;
				fixed4 col = fixed4(0,0,0,0);
				for (float j = -_Ratio*_Sigma; j <= _Ratio*_Sigma; j+=_Sigma)
				{
					for (float k = -_Ratio*_Sigma; k <= _Ratio*_Sigma; k+=_Sigma)
					{
						float2 _offset=float2(j,k)*_MainTex_TexelSize.xy;
                        float2 blurUV = i.uv + _offset;
                        if(blurUV.x >= 0 && blurUV.x <= 1 && blurUV.y >= 0 && blurUV.y <= 1)
                        {
                            //二维正态分布，公式：G(x,y)=exp(-(x²+y²)/(2σ²))/(2πσ²)
                            float weight = exp((_offset.x * _offset.x + _offset.y * _offset.y)/(-2 * _Sigma * _Sigma))/(6.2831852 * _Sigma * _Sigma);
						    col += tex2D(_MainTex, blurUV) * weight;
						    sum += weight;
                        }
					}
				}	

                return col/sum;
            }
            ENDCG
        }
    }
}

效果：