Shader "Unlit/ToolTipLine"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Color ("Tint", Color) = (1,1,1,1)
    }
    SubShader
    {
        LOD 100

        Pass
        {
            //线条未被遮挡住时，采用此Pass渲染
            Tags { "RenderType" = "Transparent" }

            Blend SrcAlpha OneMinusSrcAlpha
            ZWrite On
            ZTest LEqual

            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;
            float4 _MainTex_ST;
            fixed4 _Color;

            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;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv) * _Color;
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                //边缘渐变发光效果
                /* 普通算法
                if (i.uv.y <= 0.5)
                    col.a = smoothstep(0, 0.5, i.uv.y);
                else
                    col.a = 1 - smoothstep(0.5, 1, i.uv.y);
                */
                //优化后的算法
                col.a = smoothstep(0, 0.5, i.uv.y) * step(i.uv.y, 0.5) + (1 - smoothstep(0.5, 1, i.uv.y)) * step(0.5, i.uv.y);
                return col;
            }
            ENDCG
        }

        Pass
        {
            //线条被遮挡时，采用此Pass渲染
            Tags { "RenderType" = "Transparent" }

            Blend SrcAlpha OneMinusSrcAlpha
            ZWrite On
            ZTest Greater

            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;
            float4 _MainTex_ST;
            fixed4 _Color;

            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;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv) * _Color;
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                col.a = smoothstep(0, 0.5, i.uv.y) * step(i.uv.y, 0.5) + (1 - smoothstep(0.5, 1, i.uv.y)) * step(0.5, i.uv.y);
                col.a *= 0.1;
                return col;
            }
            ENDCG
        }
    }
}

效果截图