Shader "Custom/Outline"
{
    Properties
    {
        _MainTex ("Main Texture", 2D) = "white" {}
        _OutlineColor ("Outline Color", Color) = (1,0.5,0,1)
        _OutlineWidth ("Outline Width", Range(0, 0.5)) = 0.1
        _GlowIntensity ("Glow Intensity", Range(0, 10)) = 3
        _Falloff ("Falloff", Range(0.1, 5)) = 2
    }

    SubShader
    {
        Tags { "RenderType"="Transparent" "Queue"="Transparent" }
        LOD 100

        Pass
        {
            Cull Off
            Blend SrcAlpha OneMinusSrcAlpha
            ZWrite Off

            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;
                float2 scaledWidth : TEXCOORD1;
                float2 uvSign : TEXCOORD2;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float4 _OutlineColor;
            float _OutlineWidth;
            float _GlowIntensity;
            float _Falloff;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                
                // 计算缩放符号
                float2 scaleSign = float2(
                    sign(unity_ObjectToWorld._m00),
                    sign(unity_ObjectToWorld._m11)
                );
                
                // 修正UV方向
                o.uv = v.uv * scaleSign + (1 - scaleSign)/2;
                o.uv = TRANSFORM_TEX(o.uv, _MainTex);
                
                // 计算有效描边宽度（基于世界空间缩放）
                float2 worldScale = float2(
                    length(unity_ObjectToWorld._m00_m10_m20),
                    length(unity_ObjectToWorld._m01_m11_m21)
                );
                o.scaledWidth = _OutlineWidth / abs(worldScale) * 0.5;
                
                o.uvSign = scaleSign;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // 基础颜色采样（处理镜像）
                float2 baseUV = i.uv;
                if(i.uvSign.x < 0) baseUV.x = 1 - baseUV.x;
                if(i.uvSign.y < 0) baseUV.y = 1 - baseUV.y;
                
                fixed4 col = tex2D(_MainTex, baseUV);
                if(col.a > 0.99) return col;

                // 渐变参数初始化
                float maxDistance = length(i.scaledWidth);
                float glow = 0;

                // 多级采样实现渐变
                const int steps = 8;
                for(int s=1; s<=steps; s++)
                {
                    float progress = s/(float)steps;
                    float currentWidth = progress * maxDistance;

                    // 环形采样
                    for(float angle=0; angle<6.283; angle+=1.047) // 60度步进
                    {
                        float2 dir = float2(cos(angle), sin(angle));
                        float2 sampleUV = baseUV + dir * currentWidth;
                        fixed4 sampleCol = tex2D(_MainTex, sampleUV);

                        if(sampleCol.a > 0.95)
                        {
                            // 距离衰减计算
                            float attenuation = 1 - pow(progress, _Falloff);
                            glow += attenuation * _GlowIntensity / steps;
                            break;
                        }
                    }
                }

                // 颜色混合（非线性插值）
                float glowFactor = saturate(glow);
                fixed4 final = col;
                final.rgb = lerp(col.rgb, _OutlineColor.rgb, glowFactor);
                final.a = max(col.a, glowFactor * _OutlineColor.a);

                return final;
            }
            ENDCG
        }
    }
}