// by Mr. Chap Gipity
Shader "Custom/OutlineOnlyHDR"
{
    Properties
    {
        [HDR]_OutlineColor("Outline (HDR Emission)", Color) = (5,5,5,1)
        _OutlineWidth("Width (view-space units)", Float) = 0.02
        _ZOffset("Depth Offset (units)", Float) = 0.0
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" "Queue"="Geometry+1" }

        // We only want the silhouette halo, so we draw
        // inflated backfaces after regular geometry.
        Pass
        {
            Name "OUTLINE_ONLY"
            Tags { "LightMode"="Always" }

            Cull Front           // draw backfaces only (silhouette)
            ZWrite On
            ZTest LEqual
            Offset 0, 0          // polygon offset off by default; use _ZOffset below

            CGPROGRAM
            #pragma vertex   vert
            #pragma fragment frag
            #pragma target 3.0
            #pragma multi_compile_instancing

            #include "UnityCG.cginc"

            fixed4 _OutlineColor;
            float  _OutlineWidth;
            float  _ZOffset;

            struct appdata
            {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float4 pos : SV_POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID
                UNITY_VERTEX_OUTPUT_STEREO
            };

            v2f vert (appdata v)
            {
                v2f o;
                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_INITIALIZE_OUTPUT(v2f, o);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);

                // World space position & normal
                float3 worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
                float3 worldNrm = UnityObjectToWorldNormal(v.normal);

                // View space position & normal
                float3 viewPos = mul(UNITY_MATRIX_V, float4(worldPos, 1)).xyz;
                float3 viewNrm = normalize(mul((float3x3)UNITY_MATRIX_V, worldNrm));

                // Extrude along view-space normal for (almost) constant on-screen thickness
                viewPos += viewNrm * _OutlineWidth;

                // Optional depth nudge to avoid z-fighting at grazing angles
                viewPos.z += _ZOffset;

                // Project
                o.pos = mul(UNITY_MATRIX_P, float4(viewPos, 1));

                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // Unlit, pure emission. Use HDR color for bloom.
                return _OutlineColor;
            }
            ENDCG
        }
    }

    Fallback Off
}