Shader "Unlit/DualBlur"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Offset("BlurOffset", float) = 1
    }
    SubShader
    {
        CGINCLUDE
            #include "UnityCG.cginc"

            uniform sampler2D _MainTex;
            uniform float4 _MainTex_ST;
            uniform half _Offset;
            float4 _MainTex_TexelSize;

            struct a2f_default
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            // 降采样 顶-片结构体
            struct v2f_downSample
            {
                float4 vertex : SV_POSITION;
                float2 texcoord: TEXCOORD0;
                float2 uv: TEXCOORD1;
                float4 uv01: TEXCOORD2;
                float4 uv23: TEXCOORD3;
            };
            // 升采样 顶-片结构体
            struct v2f_upSample
            {
                float4 vertex: SV_POSITION;
                float2 texcoord: TEXCOORD0;
                float4 uv01: TEXCOORD1;
                float4 uv23: TEXCOORD2;
                float4 uv45: TEXCOORD3;
                float4 uv67: TEXCOORD4;
            };

            v2f_downSample VertDownSample(a2f_default v)
            {
                v2f_downSample o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.texcoord = v.uv;
                #if UNITY_UV_STARTS_AT_TOP
                    o.texcoord = o.texcoord * float2(1.0, -1.0) + float2(0.0, 1.0);
                #endif
                float2 uv = TRANSFORM_TEX(o.texcoord, _MainTex);
                
                _MainTex_TexelSize *= 0.5;
                o.uv = uv;
                o.uv01.xy = uv - _MainTex_TexelSize * float2(1 + _Offset, 1 + _Offset);//top right
                o.uv01.zw = uv + _MainTex_TexelSize * float2(1 + _Offset, 1 + _Offset);//bottom left
                o.uv23.xy = uv - float2(_MainTex_TexelSize.x, -_MainTex_TexelSize.y) * float2(1 + _Offset, 1 + _Offset);//top left
                o.uv23.zw = uv + float2(_MainTex_TexelSize.x, -_MainTex_TexelSize.y) * float2(1 + _Offset, 1 + _Offset);//bottom right

                return o;
            }

            half4 FragDownSample(v2f_downSample i): SV_Target
            {
                half4 sum = tex2D(_MainTex, i.uv) * 4;
                sum += tex2D(_MainTex, i.uv01.xy);
                sum += tex2D(_MainTex, i.uv01.zw);
                sum += tex2D(_MainTex, i.uv23.xy);
                sum += tex2D(_MainTex, i.uv23.zw);
                
                return half4(sum.rgb * 0.125, 1.0);
            }

            v2f_upSample VertUpSample(a2f_default v)
            {
                v2f_upSample o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.texcoord = v.uv;
                #if UNITY_UV_STARTS_AT_TOP
                    o.texcoord = o.texcoord * float2(1.0, -1.0) + float2(0.0, 1.0);
                #endif
                float2 uv = TRANSFORM_TEX(o.texcoord, _MainTex);
                
                _MainTex_TexelSize *= 0.5;
                _Offset = float2(1 + _Offset, 1 + _Offset);
                
                o.uv01.xy = uv + float2(-_MainTex_TexelSize.x * 2, 0) * _Offset;
                o.uv01.zw = uv + float2(-_MainTex_TexelSize.x, _MainTex_TexelSize.y) * _Offset;
                o.uv23.xy = uv + float2(0, _MainTex_TexelSize.y * 2) * _Offset;
                o.uv23.zw = uv + _MainTex_TexelSize * _Offset;
                o.uv45.xy = uv + float2(_MainTex_TexelSize.x * 2, 0) * _Offset;
                o.uv45.zw = uv + float2(_MainTex_TexelSize.x, -_MainTex_TexelSize.y) * _Offset;
                o.uv67.xy = uv + float2(0, -_MainTex_TexelSize.y * 2) * _Offset;
                o.uv67.zw = uv - _MainTex_TexelSize * _Offset;
                
                return o;
            }
            
            half4 FragUpSample(v2f_upSample i): SV_Target
            {
                half4 sum = 0;
                sum += tex2D(_MainTex, i.uv01.xy);
                sum += tex2D(_MainTex, i.uv01.zw) * 2;
                sum += tex2D(_MainTex, i.uv23.xy);
                sum += tex2D(_MainTex, i.uv23.zw) * 2;
                sum += tex2D(_MainTex, i.uv45.xy);
                sum += tex2D(_MainTex, i.uv45.zw) * 2;
                sum += tex2D(_MainTex, i.uv67.xy);
                sum += tex2D(_MainTex, i.uv67.zw) * 2;
                
                return half4(sum.rgb * 0.0833, 1.0);
            }
        ENDCG

        Cull Off ZWrite Off ZTest Always
		
		Pass
		{
			CGPROGRAM
			
			#pragma vertex VertDownSample
			#pragma fragment FragDownSample
			// #pragma enable_d3d11_debug_symbols
			ENDCG
			
		}
		
		Pass
		{
			CGPROGRAM
			
			#pragma vertex VertUpSample
			#pragma fragment FragUpSample
			// #pragma enable_d3d11_debug_symbols
			ENDCG
			
		}
    }
}