Shader "Unlit/LoadScreen"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _BlurRadius ("BlurRadius", Range(0, 50)) = 0  //模糊半径
		_TextureSize ("TextureSize", Float) = 640 
		_SecTex("SecTex",2D) = "white" {}
    }
    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;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            sampler2D _SecTex;
            float4 _MainTex_ST;
            int _BlurRadius;
			float _TextureSize;
			float GetGaussWeight(float x, float y, float sigma)
			{
				float sigma2 = pow(sigma, 2.0f);		
				float left = 1 / (2 * sigma2 * 3.1415926f);
				float right = exp(-(x*x+y*y)/(2*sigma2));	 //e的指数幂
				return left * right;
			}
			
			float4 GaussBlur(float2 uv)		 //高斯公式
			{
				float sigma = (float)_BlurRadius / 3.0f;//权重
				float4 col = float4(0, 0, 0, 0);
				for (int x = - _BlurRadius; x <= _BlurRadius; ++x)
				{
					for (int y = - _BlurRadius; y <= _BlurRadius; ++y)
					{
						//获取周围像素的颜色
						//转为uv上的坐标值
						float4 color = tex2D(_SecTex, uv + float2(x / _TextureSize, y / _TextureSize));
						//获取此像素的权重
						float weight = GetGaussWeight(x, y, sigma);
						//计算此点的最终颜色
						col += color * weight;	//颜色乘以权重
					}
				}
				return col;
			}

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

            float4 frag (v2f i) : SV_Target
            {
                float4 black = float4(0,0,0,0);
                float4 col = GaussBlur(i.uv);
                col*=1+_BlurRadius;
                col=smoothstep(0.1,0.9,col);
                col=step(col,0.5);
                col*=tex2D(_MainTex,i.uv);
                col = lerp(col,black,_BlurRadius*(1.0/50));
                return col;
            }
            ENDCG
        }
    }
}