MatCap shader imitation of blender 2.8s matcap

[mr-hog]

Hello I’m trying to make a blender2.8 matcap imitation so far its fairly good , the error is in the corners (hopefully i have the image attached correctly , black with white edges) , i don’t really know how to fix my mistake the idea is to use a dot product on a surface to eye vector with a tangent of the normals.
thanks.

Shader "Unlit/matcatallsurface_vf"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _MatCap ("matcap",2D) = "black" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
        Tags { "LightMode" = "Always" }
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
           

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                float3 normal : NORMAL;
        
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
                float2 mat : TEXCOORD1;
                
            };

            sampler2D _MainTex , _MatCap;
            float4 _MainTex_ST;
           
            v2f vert (appdata v)
            {
                v2f o;

                float3 worldPos = mul(unity_ObjectToWorld, v.vertex);
                float3 worldNormal = mul(unity_ObjectToWorld, v.normal);
                float3 toCam = normalize(_WorldSpaceCameraPos.xyz - worldPos);

                float3 cx = normalize( cross(-worldNormal, UNITY_MATRIX_V[1]) );
                float3 cy = normalize( cross(-worldNormal, UNITY_MATRIX_V[0]) );

                o.mat = float2( dot(toCam, cx) , dot(toCam, -cy) )*.5+.5;

                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
           
                return o;
            }
           
            fixed4 frag (v2f i) : SV_Target
            {
               
                fixed4 col = tex2D(_MainTex, i.uv);
                fixed4 matcap = tex2D(_MatCap, i.mat.xy);
                return col *2*matcap;
            }
            ENDCG
        }
    }
}

[mr-hog]

Ok my main problem seems to be in normalizing the cross product instead of getting something like (1,1) getting (.7,.7) for a length of 1,the above code has mat removed form appdata by accident trying to clean up post .
the odd problem now is serious curvature when looking at a similar surfaces of the viewing angle.