Shader "Custom/InvertShader"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        // No culling or depth
        Cull Off ZWrite Off ZTest Always

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;

                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;

                UNITY_VERTEX_OUTPUT_STEREO
            };

            v2f vert(appdata v)
            {
                v2f o;

                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_INITIALIZE_OUTPUT(v2f, o); //Insert
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o); //Insert

                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            //sampler2D _MainTex;
            UNITY_DECLARE_SCREENSPACE_TEXTURE(_MainTex); //Insert

            fixed4 frag(v2f i) : SV_Target
            {
                UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i); //Insert

                fixed4 col = UNITY_SAMPLE_SCREENSPACE_TEXTURE(_MainTex, i.uv); //Insert
                // just invert the colors
                col.rgb = 1 - col.rgb;
                return col;
            }
            ENDCG
        }
    }
}