Shader "Custom/HexGridSimple"
{
    Properties
    {
        _BaseColor  ("Base Color (alpha 0 = прозрачный)", Color) = (0,0,0,0)
        _LineColor  ("Line Color", Color) = (1,1,1,1)
        _CellSize   ("Cell Size (радиус шестигранника)", Float) = 1
        _LineWidth  ("Line Width (доля от размера клетки)", Range(0.001, 0.5)) = 0.05
        _GridOrigin ("Grid Origin (XZ)", Vector) = (0,0,0,0)
    }
    SubShader
    {
        Tags { "RenderType"="Transparent" "Queue"="Transparent" "RenderPipeline"="UniversalPipeline" }

        Pass
        {
            Name "HexGrid"
            Tags { "LightMode"="UniversalForward" }
            Blend One OneMinusSrcAlpha      // premultiplied alpha
            ZWrite Off
            Cull Off

            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            CBUFFER_START(UnityPerMaterial)
                half4  _BaseColor;
                half4  _LineColor;
                float  _CellSize;
                float  _LineWidth;
                float4 _GridOrigin;
            CBUFFER_END

            struct Attributes { float4 positionOS : POSITION; };
            struct Varyings   { float4 positionCS : SV_POSITION; float3 positionWS : TEXCOORD0; };

            Varyings vert(Attributes IN)
            {
                Varyings OUT;
                OUT.positionWS = TransformObjectToWorld(IN.positionOS.xyz);
                OUT.positionCS = TransformWorldToHClip(OUT.positionWS);
                return OUT;
            }

            static const float SQRT3 = 1.7320508;
            static const float HALF_SQRT3 = 0.8660254;

            // Центр шестигранника, содержащего точку p (pointy-top, R = радиус описанной окружности)
            float2 HexCenter(float2 p, float R)
            {
                float q = (SQRT3 / 3.0 * p.x - 1.0 / 3.0 * p.y) / R;
                float r = (2.0 / 3.0 * p.y) / R;
                float3 c  = float3(q, -q - r, r);     // cube
                float3 rc = round(c);
                float3 d  = abs(rc - c);
                if (d.x > d.y && d.x > d.z) rc.x = -rc.y - rc.z;
                else if (d.y > d.z)         rc.y = -rc.x - rc.z;
                else                        rc.z = -rc.x - rc.y;
                return float2(R * SQRT3 * (rc.x + rc.z * 0.5), R * 1.5 * rc.z);
            }

            // Расстояние от точки (относительно центра) до ближайшего ребра
            float HexEdgeDist(float2 d, float R)
            {
                float h = max(abs(d.x),
                          max(abs( 0.5 * d.x + HALF_SQRT3 * d.y),
                              abs(-0.5 * d.x + HALF_SQRT3 * d.y)));
                return HALF_SQRT3 * R - h;
            }

            half4 frag(Varyings IN) : SV_Target
            {
                float2 p = IN.positionWS.xz - _GridOrigin.xy;
                float2 c = HexCenter(p, _CellSize);
                float  e = HexEdgeDist(p - c, _CellSize);

                float t  = 0.5 * _LineWidth * _CellSize;   // половина толщины линии
                float aa = fwidth(e);
                float lineMask = 1.0 - smoothstep(t - aa, t + aa, e);

                half4 b = half4(_BaseColor.rgb * _BaseColor.a, _BaseColor.a);
                half4 l = half4(_LineColor.rgb * _LineColor.a, _LineColor.a);
                return lerp(b, l, lineMask);
            }
            ENDHLSL
        }
    }
}