Shader "VRTK/OutlineBasic"
{
    Properties
    {
        _OutlineColor("Outline Color", Color) = (1, 0, 0, 1)
        _Thickness("Thickness", float) = 1
    }

    SubShader
    {
        Tags
        {
            "Queue" = "Transparent"
            "IgnoreProjector" = "True"
            "RenderType" = "Transparent"
        }

        // Fill the stencil buffer
        Pass
        {
            Stencil
            {
                Ref 1
                Comp Always
                Pass Replace
                ZFail Replace
            }

            ColorMask 0
        }

        // Draw the outline
        Pass
        {
            Blend SrcAlpha OneMinusSrcAlpha
            ZWrite Off // On (default) = Ignore lights etc. Should this be a property?
            Stencil
            {
                Ref 0
                Comp Equal
            }

            CGPROGRAM
                #pragma vertex vert
                #pragma geometry geom
                #pragma fragment frag

                #include "UnityCG.cginc"
                half4 _OutlineColor;
                float _Thickness;

                struct appdata
                {
                    float4 vertex : POSITION;
                };

                struct v2g
                {
                    float4 pos : SV_POSITION;
                };

                v2g vert(appdata IN)
                {
                    v2g OUT;
                    OUT.pos = UnityObjectToClipPos(IN.vertex);
                    return OUT;
                }

                void geom2(v2g start, v2g end, inout TriangleStream<v2g> triStream)
                {
                    float width = _Thickness / 100;
                    float4 parallel = (end.pos - start.pos) * width;
                    float4 perpendicular = normalize(float4(parallel.y, -parallel.x, 0, 0)) * width;
                    float4 v1 = start.pos - parallel;
                    float4 v2 = end.pos + parallel;
                    v2g OUT;
                    OUT.pos = v1 - perpendicular;
                    triStream.Append(OUT);
                    OUT.pos = v1 + perpendicular;
                    triStream.Append(OUT);
                    OUT.pos = v2 - perpendicular;
                    triStream.Append(OUT);
                    OUT.pos = v2 + perpendicular;
                    triStream.Append(OUT);
                }

                [maxvertexcount(12)]
                void geom(triangle v2g IN[3], inout TriangleStream<v2g> triStream)
                {
                    geom2(IN[0], IN[1], triStream);
                    geom2(IN[1], IN[2], triStream);
                    geom2(IN[2], IN[0], triStream);
                }

                half4 frag(v2g IN) : COLOR
                {
                    _OutlineColor.a = 1;
                    return _OutlineColor;
                }
            ENDCG
        }
    }
    FallBack "Diffuse"
}