はしっこをグラデにするシェーダー

Shader "Unlit/AboutBg"
{
    Properties
    {
        _Width ("_Width", float) = 30
    }
    SubShader
    {
        Tags {"Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent"}
        LOD 100
        
        ZWrite Off
        Blend SrcAlpha OneMinusSrcAlpha

        Pass
        {
            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;
            };

            float _Width;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.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 = fixed4(0,0,0,1);
                
                float ww = _Width;
                float hh = _Width * _ScreenParams.y/_ScreenParams.x;

                float x0 = saturate( abs(i.uv.x)*ww );//はしっこほど０
                float x1 = saturate( abs(1-i.uv.x)*ww );//はしっこほど０
                float y0 = saturate( abs(i.uv.y)*hh );//はしっこほど０
                float y1 = saturate( abs(1-i.uv.y)*hh );//はしっこほど０

                float value = 1-min( min(y0,y1),min(x0,x1) );
                //col.rgb = 
                col.a = value;
                //col.a = (1 - col.a);

                // apply fog
                //UNITY_APPLY_FOG(i.fogCoord, col);
                return col;
            }
            ENDCG
        }
    }
}