高斯模糊-原理类似近视眼

实现ps里用过的模糊效果，还是挺有意思的！ 

Shader "Unlit/gaussian_blur"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
		_GaussianBlur("高斯模糊值",Range(0.001,0.01)) = 0.001
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag

			
			#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;
			float _GaussianBlur;

			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
			{
				// sample the texture
				float2 tempUV = i.uv;

				fixed4 col = tex2D(_MainTex, tempUV);//原来的颜色值
				fixed4 col1 = tex2D(_MainTex, tempUV + float2(-_GaussianBlur,0));//叠加左边的颜色
				fixed4 col2 = tex2D(_MainTex, tempUV + float2(_GaussianBlur,0));//叠加右边的颜色
				fixed4 col3 = tex2D(_MainTex, tempUV + float2(0,-_GaussianBlur));//叠加下边的颜色
				fixed4 col4 = tex2D(_MainTex, tempUV + float2(0,_GaussianBlur));//叠加上边的颜色
				col = (col + col1 + col2 + col3 + col4)/5;//取平均值
				//_GaussianBlur的值越大“聚焦”越模糊，就像近视一样
				return col;
			}
			ENDCG
		}
	}
}