Demo 51 - Discard faces

Shader "Custom/FrontFaces"
{
    Properties
    {
        _MainTex ("Main Texture", 2D) = "white" {}
        _ScalarVal ("Value", Range(0.0, 1.0)) = 0.0
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        Pass {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            struct v2f {
                float4 pos : SV_POSITION;
                half2 uv : TEXCOORD0;
                fixed val : TEXCOORD1;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            half _ScalarVal;

            v2f vert(appdata_base v) {
                v2f o;
                float4 worldpos = mul(unity_ObjectToWorld, v.vertex);
                o.pos = mul(UNITY_MATRIX_VP, worldpos);
                o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);

                float3 worldnormal = normalize(mul(v.normal, (float3x3)unity_WorldToObject));

                if(dot(worldnormal, normalize(_WorldSpaceCameraPos.xyz - worldpos.xyz)) > _ScalarVal)
                    o.val = 1;
                else
                    o.val = 0;
                return o;
            }

            fixed4 frag(v2f i) : SV_Target {
                if(i.val < 0.99) discard;
                fixed4 col = tex2D(_MainTex, i.uv);
                return col;
            }

            ENDCG
        }
    }
}