Shader "Custom/2D/OutlineShape"
{
    Properties
    {
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
        
        [Header(Base Settings)]
        [MainColor] [HDR] _BaseColor ("Base Color (本身颜色)", Color) = (1,1,1,1)
        [Range(0, 1)] _BaseAlpha ("Base Alpha (本体透明度)", Float) = 1.0
        
        [Space(10)]
        [Header(Outline Settings)]
        [Toggle(_OUTLINE_ON)] _EnableOutline("Enable Outline (启用描边)", Float) = 1
        [HDR] _OutlineColor ("Outline Color (描边颜色)", Color) = (1, 1, 0, 1)
        [Range(0, 50)] _OutlineWidth ("Outline Width (描边粗细 像素)", Float) = 5.0
        [Range(0.01, 1)] _AlphaThreshold ("Inner Threshold (内描边判定阈值:寻找边界)", Float) = 0.5
        [Range(0.01, 1)] _OutlineSmoothness ("Outline Smoothness (描边平滑度:抗锯齿)", Float) = 0.2

        // Below properties are required for SpriteRenderer internal data passing and ETC1 support
        [HideInInspector] _RendererColor ("RendererColor", Color) = (1,1,1,1)
        [HideInInspector] _Flip ("Flip", Vector) = (1,1,1,1)
        [HideInInspector] _AlphaTex ("External Alpha", 2D) = "white" {}
        [HideInInspector] _EnableExternalAlpha ("Enable External Alpha", Float) = 0
    }

    SubShader
    {
        Tags
        { 
            "RenderPipeline" = "UniversalPipeline"
            "Queue" = "Transparent"
            "RenderType" = "Transparent"
            "IgnoreProjector" = "True"
            "PreviewType" = "Plane"
            "CanUseSpriteAtlas" = "True"
        }

        Cull Off
        Lighting Off
        ZWrite Off
        Blend SrcAlpha OneMinusSrcAlpha

        Pass
        {
            Name "SpriteOutline"

            HLSLPROGRAM
            #pragma target 2.0
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_local _ ETC1_EXTERNAL_ALPHA
            // 新增: 基于本地关键字的着色器变体，如果关闭描边，将彻底剔除描边代码
            #pragma shader_feature_local_fragment _OUTLINE_ON

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

            struct Attributes
            {
                float3 positionOS   : POSITION;
                float4 color        : COLOR;
                float2 uv           : TEXCOORD0;
            };

            struct Varyings
            {
                float4 positionCS   : SV_POSITION;
                float2 uv           : TEXCOORD0;
                half4 color         : COLOR;
            };

            TEXTURE2D(_MainTex);
            SAMPLER(sampler_MainTex);
            float4 _MainTex_TexelSize;

            #if defined(ETC1_EXTERNAL_ALPHA)
                TEXTURE2D(_AlphaTex);
                SAMPLER(sampler_AlphaTex);
            #endif

            CBUFFER_START(UnityPerMaterial)
                half4 _BaseColor;
                half _BaseAlpha;
                half4 _OutlineColor;
                float _OutlineWidth;
                float _AlphaThreshold;
                float _OutlineSmoothness;
                half4 _RendererColor;
                float4 _Flip;
                float _EnableExternalAlpha;
            CBUFFER_END

            Varyings vert(Attributes IN)
            {
                Varyings OUT;
                float3 pos = IN.positionOS;
                pos.xy *= _Flip.xy;

                OUT.positionCS = TransformObjectToHClip(pos);
                OUT.uv = IN.uv;
                
                // 注意这里颜色相乘，但不包括 Alpha，Alpha后续单独计算
                OUT.color = IN.color * _BaseColor * _RendererColor;
                return OUT;
            }

            half SampleSpriteAlpha(float2 uv)
            {
                // 若 UV 超出单张贴图边界(0~1)，强制视作完全透明。
                // 这解决了因图片边缘紧贴画布，受 Wrap Mode(Clamp/Repeat) 影响导致无法检测到外部透明度的问题
                if (any(uv < 0.0) || any(uv > 1.0))
                {
                    return 0.0;
                }

                half a = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv).a;
                #if defined(ETC1_EXTERNAL_ALPHA)
                if (_EnableExternalAlpha > 0.0)
                {
                    a = SAMPLE_TEXTURE2D(_AlphaTex, sampler_AlphaTex, uv).r;
                }
                #endif
                return a;
            }
            
            half3 SampleSpriteRGB(float2 uv)
            {
                 half4 col = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv);
                 return col.rgb;
            }

            half4 frag(Varyings IN) : SV_Target
            {
                // 1. 获取当前像素原始Alpha
                half originalAlpha = SampleSpriteAlpha(IN.uv);
                half baseAlphaMultiplier = IN.color.a;

                // 若原图毫无 Alpha，极其干净地剔除，提高性能
                if (originalAlpha < 0.01)
                {
                    return half4(0,0,0,0);
                }

                #if defined(_OUTLINE_ON)
                // --- 开启描边的情况 ---

                // 2. 多重采样寻找该像素周围一定范围内，Alpha的最小值
                float2 offsetX = float2(_MainTex_TexelSize.x, 0.0) * _OutlineWidth;
                float2 offsetY = float2(0.0, _MainTex_TexelSize.y) * _OutlineWidth;
                float2 offsetDiag = float2(_MainTex_TexelSize.x, _MainTex_TexelSize.y) * _OutlineWidth * 0.7071;

                half minAlpha = originalAlpha;
                
                minAlpha = min(minAlpha, SampleSpriteAlpha(IN.uv + offsetX));
                minAlpha = min(minAlpha, SampleSpriteAlpha(IN.uv - offsetX));
                minAlpha = min(minAlpha, SampleSpriteAlpha(IN.uv + offsetY));
                minAlpha = min(minAlpha, SampleSpriteAlpha(IN.uv - offsetY));

                minAlpha = min(minAlpha, SampleSpriteAlpha(IN.uv + offsetDiag));
                minAlpha = min(minAlpha, SampleSpriteAlpha(IN.uv - offsetDiag));
                minAlpha = min(minAlpha, SampleSpriteAlpha(IN.uv + float2(-offsetDiag.x, offsetDiag.y)));
                minAlpha = min(minAlpha, SampleSpriteAlpha(IN.uv + float2(offsetDiag.x, -offsetDiag.y)));

                // 3. 计算“这是否是一个描边像素” (0:本体, 1:描边)
                half isEdge = 1.0 - smoothstep(_AlphaThreshold - _OutlineSmoothness, _AlphaThreshold + _OutlineSmoothness, minAlpha);

                // 4. 透明度混合
                half finalObjectAlpha = originalAlpha * baseAlphaMultiplier * _BaseAlpha;
                half finalOutlineAlpha = originalAlpha * baseAlphaMultiplier * _OutlineColor.a;
                half finalAlpha = lerp(finalObjectAlpha, finalOutlineAlpha, isEdge);
                
                // 5. 计算颜色
                half3 rawColor = SampleSpriteRGB(IN.uv) * IN.color.rgb; // 包含了BaseColor
                half3 finalRGB = lerp(rawColor, _OutlineColor.rgb, isEdge);

                return half4(finalRGB, finalAlpha);
                
                #else
                // --- 关闭描边的情况，以极低开销渲染原本材质 ---
                
                half finalObjectAlpha = originalAlpha * baseAlphaMultiplier * _BaseAlpha;
                half3 rawRGB = SampleSpriteRGB(IN.uv) * IN.color.rgb;

                return half4(rawRGB, finalObjectAlpha);
                
                #endif
            }
            ENDHLSL
        }
    }
}