// XC_BUILTIN_INFINITE_GRID_D3D12_PS
cbuffer GridConstants : register(b0) {
    float4x4 gViewProjectionMatrix;
    float4 gCameraPositionAndScale;
    float4 gCameraRightAndFade;
    float4 gCameraUpAndTanHalfFov;
    float4 gCameraForwardAndAspect;
    float4 gViewportNearFar;
    float4 gGridTransition;
};

struct VSOutput {
    float4 position : SV_POSITION;
};

float PristineGridLine(float2 uv) {
    float2 deriv = max(fwidth(uv), float2(1e-6, 1e-6));
    float2 uvMod = frac(uv);
    float2 uvDist = min(uvMod, 1.0 - uvMod);
    float2 distInPixels = uvDist / deriv;
    float2 lineAlpha = 1.0 - smoothstep(0.0, 1.0, distInPixels);
    float density = max(deriv.x, deriv.y);
    float densityFade = 1.0 - smoothstep(0.5, 1.0, density);
    return max(lineAlpha.x, lineAlpha.y) * densityFade;
}

float AxisLineAA(float coord, float deriv) {
    float distInPixels = abs(coord) / max(deriv, 1e-6);
    return 1.0 - smoothstep(0.0, 1.5, distInPixels);
}

struct GridLayer {
    float minor;
    float major;
};

GridLayer SampleGridLayer(float2 worldPos2D, float baseScale) {
    GridLayer layer;
    const float2 gridCoord1 = worldPos2D / baseScale;
    const float2 gridCoord10 = worldPos2D / (baseScale * 10.0);
    const float grid1 = PristineGridLine(gridCoord1);
    const float grid10 = PristineGridLine(gridCoord10);
    const float2 deriv1 = fwidth(gridCoord1);
    const float lodFactor = smoothstep(0.3, 0.6, max(deriv1.x, deriv1.y));

    layer.major = max(grid10, grid1 * 0.35);
    layer.minor = grid1 * (1.0 - lodFactor);
    return layer;
}

struct PSOutput {
    float4 color : SV_TARGET0;
    float depth : SV_Depth;
};

PSOutput MainPS(VSOutput input) {
    const float2 viewportSize = max(gViewportNearFar.xy, float2(1.0, 1.0));
    const float scale = max(gCameraPositionAndScale.w, 1e-4);
    const float fadeDistance = max(gCameraRightAndFade.w, scale * 10.0);
    const float tanHalfFov = max(gCameraUpAndTanHalfFov.w, 1e-4);
    const float aspect = max(gCameraForwardAndAspect.w, 1e-4);
    const float transitionBlend = saturate(gGridTransition.x);
    const float nearClip = gViewportNearFar.z;
    const float sceneFarClip = gViewportNearFar.w;

    const float2 ndc = float2(
        (input.position.x / viewportSize.x) * 2.0 - 1.0,
        1.0 - (input.position.y / viewportSize.y) * 2.0);

    const float3 cameraPosition = gCameraPositionAndScale.xyz;
    const float3 rayDirection = normalize(
        gCameraForwardAndAspect.xyz +
        ndc.x * aspect * tanHalfFov * gCameraRightAndFade.xyz +
        ndc.y * tanHalfFov * gCameraUpAndTanHalfFov.xyz);

    if (abs(rayDirection.y) < 1e-5) {
        discard;
    }

    const float t = -cameraPosition.y / rayDirection.y;
    if (t <= nearClip) {
        discard;
    }

    const float3 worldPosition = cameraPosition + rayDirection * t;
    float depth = 0.999999;
    if (t < sceneFarClip) {
        const float4 clipPosition = mul(gViewProjectionMatrix, float4(worldPosition, 1.0));
        if (clipPosition.w <= 1e-6) {
            discard;
        }

        depth = clipPosition.z / clipPosition.w;
        if (depth <= 0.0 || depth >= 1.0) {
            discard;
        }
    }

    const float radialFade =
        1.0 - smoothstep(fadeDistance * 0.3, fadeDistance, length(worldPosition - cameraPosition));
    const float normalFade = smoothstep(0.0, 0.15, abs(rayDirection.y));
    const float fadeFactor = radialFade * normalFade;
    if (fadeFactor < 1e-3) {
        discard;
    }

    const float2 worldPos2D = worldPosition.xz;
    const GridLayer baseLayer = SampleGridLayer(worldPos2D, scale);
    const GridLayer nextLayer = SampleGridLayer(worldPos2D, scale * 10.0);
    const float minorGridIntensity = lerp(baseLayer.minor, nextLayer.minor, transitionBlend);
    const float majorGridIntensity = lerp(baseLayer.major, nextLayer.major, transitionBlend);
    float3 finalColor = float3(0.56, 0.56, 0.56);
    float finalAlpha = max(
        0.13 * minorGridIntensity * fadeFactor,
        0.28 * majorGridIntensity * fadeFactor);

    const float2 worldDeriv = max(fwidth(worldPos2D), float2(1e-6, 1e-6));
    const float xAxisAlpha = AxisLineAA(worldPos2D.y, worldDeriv.y) * fadeFactor;
    const float zAxisAlpha = AxisLineAA(worldPos2D.x, worldDeriv.x) * fadeFactor;

    const float axisAlpha = max(xAxisAlpha, zAxisAlpha);
    finalAlpha = max(finalAlpha, 0.34 * saturate(axisAlpha));

    if (finalAlpha < 1e-3) {
        discard;
    }

    PSOutput output;
    output.color = float4(finalColor, finalAlpha);
    output.depth = depth;
    return output;
}