Shader "Soullies/DTM_RegularGridFloor"
{
    Properties
    {
        [HDR]_Color0("Color0", Color) = (1, 1, 1, 0)
        
        [Header(Grid Settings)]
        _GridSize("Grid Size (X, Y)", Vector) = (1.0, 1.0, 0, 0)
        _GridDensity("Grid Density (Quantity Multiplier)", Float) = 1.0
        
        _LineThickness("Line Thickness", Range(0.001, 0.5)) = 0.05
        
        _EdgeSoftness("Edge Softness", Range(0.0, 0.5)) = 0.01

        [Header(Animation Settings)]
        _MoveVector("Movement Vector (X, Y)", Vector) = (0.0, 1.0, 0, 0)

        [Header(Outer Enclosing Border)]
        [Toggle(_OUTER_BORDER_ON)] _EnableOuterBorder("Enable Outer Border", Float) = 0
        [HDR] _OuterBorderColor("Outer Border Color", Color) = (1, 1, 1, 1)
        _OuterBorderWidth("Outer Border Width", Range(0.0, 0.5)) = 0.02
        
        [Header(Render State)]
        [Enum(UnityEngine.Rendering.BlendMode)] _SrcBlend("Src Blend", Float) = 5 // SrcAlpha
        [Enum(UnityEngine.Rendering.BlendMode)] _DstBlend("Dst Blend", Float) = 10 // OneMinusSrcAlpha
        [Enum(Off, 0, On, 1)] _ZWrite("Z Write", Float) = 0
    }

    SubShader
    {
        Tags 
        { 
            "RenderPipeline" = "UniversalPipeline"
            "RenderType" = "Transparent" 
            "Queue" = "Transparent-300" 
            "UniversalMaterialType" = "Unlit"
            "IgnoreProjector" = "True"
        }

        Blend [_SrcBlend] [_DstBlend]
        ZWrite [_ZWrite]
        Cull Back
        
        Pass
        {
            Name "ForwardOnly"
            Tags { "LightMode" = "UniversalForwardOnly" }

            HLSLPROGRAM
            #pragma target 4.5
            #pragma prefer_hlslcc gles
            #pragma multi_compile_instancing
            #pragma multi_compile_fog
            #pragma shader_feature_local _OUTER_BORDER_ON

            #pragma vertex vert
            #pragma fragment frag

            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            struct Attributes
            {
                float4 positionOS   : POSITION;
                float2 uv           : TEXCOORD0;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct Varyings
            {
                float4 positionCS   : SV_POSITION;
                float3 positionWS   : TEXCOORD0;
                float2 uv           : TEXCOORD1;
                half   fogFactor    : TEXCOORD2;
                UNITY_VERTEX_INPUT_INSTANCE_ID
                UNITY_VERTEX_OUTPUT_STEREO
            };

            CBUFFER_START(UnityPerMaterial)
                half4 _Color0;
                float4 _GridSize;
                float  _GridDensity;
                float  _LineThickness;
                float  _EdgeSoftness;
                float4 _MoveVector;
                half4  _OuterBorderColor;
                float  _OuterBorderWidth;
            CBUFFER_END

            Varyings vert(Attributes input)
            {
                Varyings output = (Varyings)0;
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_TRANSFER_INSTANCE_ID(input, output);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(output);

                VertexPositionInputs vertexInput = GetVertexPositionInputs(input.positionOS.xyz);
                output.positionCS = vertexInput.positionCS;
                output.positionWS = vertexInput.positionWS;
                output.uv         = input.uv;
                output.fogFactor  = ComputeFogFactor(vertexInput.positionCS.z);

                return output;
            }

            half4 frag(Varyings input) : SV_Target
            {
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);

                // ==========================================
                // 1. Regular Grid Pattern (World Space UV)
                // ==========================================
                float2 worldUV = input.positionWS.xz;

                // Direct Linear Movement Animation
                float t = _Time.y; // Standard time in seconds
                worldUV -= _MoveVector.xy * t;

                // Density Multiplier
                float density = max(_GridDensity, 0.0001);
                float2 sizeDivisor = max(_GridSize.xy, float2(0.0001, 0.0001)) / density;
                
                // Scale UV
                float2 scaledUV = worldUV / sizeDivisor;

                // Generate pure regular grid lines mathematically
                // frac() maps to [0,1], we subtract 0.5 and take absolute to get a pyramid [0, 0.5]
                float2 cellUV = abs(frac(scaledUV) - 0.5); 
                
                // Distance to the closest grid edge
                float2 distToLine = 0.5 - cellUV;
                float closestLine = min(distToLine.x, distToLine.y);

                // Hardware screen-space derivative + Software Softness for AA
                float fw = fwidth(closestLine);
                float halfThickness = _LineThickness * 0.5;
                float edgeSoft = max(_EdgeSoftness, fw); // ensures it never hard aliases

                // Solid line with anti-aliased trailing edge
                float gridAlphaMask = smoothstep(halfThickness + edgeSoft, halfThickness - edgeSoft, closestLine);

                half3 gridColor = _Color0.rgb;
                half  gridAlpha = gridAlphaMask * _Color0.a;

                // ==========================================
                // 2. Outer Enclosing Border
                // ==========================================
                half3 finalColor = gridColor;
                half  finalAlpha = gridAlpha;

                #if defined(_OUTER_BORDER_ON)
                    // Calculate distance to nearest Mesh UV edge [0, 1]
                    float2 edgeDist = min(input.uv, 1.0 - input.uv);
                    float closestEdge = min(edgeDist.x, edgeDist.y);
                    
                    float borderfw = fwidth(closestEdge);
                    
                    // Creates a solid border with a smooth antialiased inner falloff
                    float borderMask = 1.0 - smoothstep(_OuterBorderWidth - borderfw, _OuterBorderWidth + borderfw, closestEdge);
                    
                    // Lerp grid to border
                    finalColor = lerp(gridColor, _OuterBorderColor.rgb, borderMask);
                    finalAlpha = lerp(gridAlpha, _OuterBorderColor.a, borderMask);
                #endif

                // Apply URP Fog
                finalColor = MixFog(finalColor, input.fogFactor);

                return half4(finalColor, finalAlpha);
            }
            ENDHLSL
        }
    }
    FallBack "Hidden/Universal Render Pipeline/FallbackError"
}