Shader "URP_Test/PostOutline_2"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _SampleDistance ("SampleDistance", Float) = 0.01
    }
    SubShader
    {
        Tags
        {
            "RenderType"="Opaque"
            "RenderPipeline" = "UniversalPipeline"
        }

        Cull Off 
        ZWrite Off 
        ZTest Off

        Pass
        {
            Name "DrawEdge"
            // 轮廓
            HLSLPROGRAM
            #pragma vertex VERT
            #pragma fragment FRAG
            #pragma target 2.0

            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            CBUFFER_START(UnityPerMaterial)

                float4 _MainTex_TexelSize;
                float _SampleDistance;

            CBUFFER_END
            
            TEXTURE2D(_MainTex);
            SAMPLER(sampler_MainTex);

            struct a2v
            {
                float4 positionOS   : POSITION;
                float2 uv0          : TEXCOORD;
            };

            struct v2f
            {
                float4 positionCS : SV_POSITION;
                float4 texcoord0  : TEXCOORD0;
            };

            v2f VERT(a2v i)
            {
                v2f o;
                o.positionCS = TransformObjectToHClip(i.positionOS.xyz);
                o.texcoord0 = float4(i.uv0, _SampleDistance * _MainTex_TexelSize.x, _SampleDistance * _MainTex_TexelSize.y);
                return o;
            }

            half4 FRAG(v2f i):SV_TARGET
            {
                half4 centerCol = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord0.xy);
                half offsetX = i.texcoord0.z;
                half offsetY = i.texcoord0.w;
                half4 leftCol = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord0.xy + float2(-offsetX, 0));
                half4 rightCol = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord0.xy + float2(offsetX, 0));
                half4 upCol = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord0.xy + float2(0, offsetY));
                half4 downCol = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord0.xy + float2(0, -offsetY));
                // // 左下角
                // half4 leftDownCol = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord0.xy + float2(-offsetX, -offsetY));
                // // 右下角
                // half4 rightDownCol = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord0.xy + float2(offsetX, -offsetY));
                // // 左上角
                // half4 leftUpCol = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord0.xy + float2(-offsetX, offsetY));
                // // 右上角
                // half4 rightUpCol = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord0.xy + float2(offsetX, offsetY));

                // 检测是否是边缘，保持 left -> right -> up -> down 的优先级
                half centerMask = 1.0h - step(0.5h, centerCol.a);
                half leftMask = centerMask * (1.0h - step(leftCol.a, 0.5h));
                half rightMask = centerMask * (1.0h - leftMask) * (1.0h - step(rightCol.a, 0.5h));
                half upMask = centerMask * (1.0h - leftMask) * (1.0h - rightMask) * (1.0h - step(upCol.a, 0.5h));
                half downMask = centerMask * (1.0h - leftMask) * (1.0h - rightMask) * (1.0h - upMask) * (1.0h - step(downCol.a, 0.5h));
                half3 edgeColor = leftCol.xyz * leftMask
                    + rightCol.xyz * rightMask
                    + upCol.xyz * upMask
                    + downCol.xyz * downMask;
                half edgeAlpha = saturate(leftMask + rightMask + upMask + downMask);
                return half4(edgeColor, edgeAlpha);
            }

            ENDHLSL
        }
        
    }
}