Help getting blob shadow using stencil buffer to work

Unity Engine
1

Hi all,
I’m trying to wrap my head around the use of stencil buffer by doing a simple blob shadow with it but I’m not getting the expected result.

2285023--153510--shadow.jpg
2285023--153510--shadow.jpg1000×349 59.9 KB

It seems simple in theory, but I’m unable to get the back facing polygons to clear the stencil buffer. Here’s my attempt using a single shader pass. Any ideas? Thanks!

Shader code

Shader "Custom/Stencil Shadow" {
    Properties {
        _Color ("Color", Color) = (1,1,1,1)
    }
    SubShader {
        Tags { "RenderType"="Opaque" "Queue"="Geometry-1"}

Pass {
//            ZWrite Off
            Cull Off
            Lighting Off
            Blend DstColor OneMinusSrcAlpha
           
            Stencil {
                Ref 0
                ReadMask 1
                WriteMask 1
               
                CompFront Equal            // Front
                PassFront IncrSat
//                FailFront Keep
//                ZFailFront Keep
               
                CompBack Greater        // Back
//                PassBack Keep
//                FailBack Keep
                ZFailBack IncrSat
            }
       
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            struct appdata {
                float4 vertex : POSITION;
            };
            struct v2f {
                float4 pos : SV_POSITION;
            };
            v2f vert(appdata v) {
                v2f o;
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                return o;
            }
            half4 frag(v2f i) : SV_Target {
                return half4(0,0,0,0.5);
            }
            ENDCG
        }

    }
    FallBack "Diffuse"
}
2

I too want to do that, to use as light Toon, nobody knows how to do that? it would be fabulous.