阴影图集边缘突然变暗：PCF 卷积核不能越过瓦片所有权

public readonly record struct Int2(int X, int Y);
public readonly record struct Tap(int X, int Y);

public readonly record struct TileRect(int MinX, int MinY, int Width, int Height)
{
    public int MaxX => checked(MinX + Width - 1);
    public int MaxY => checked(MinY + Height - 1);
}

public static class ShadowAtlasPcf
{
    public static Tap[] BuildKernel(
        Int2 atlasSize,
        TileRect tile,
        double localU,
        double localV,
        int radius,
        bool clampToTile)
    {
        Validate(atlasSize, tile, localU, localV, radius);

        var centerX = tile.MinX + localU * tile.Width - 0.5;
        var centerY = tile.MinY + localV * tile.Height - 0.5;
        var taps = new Tap[checked((radius * 2 + 1) * (radius * 2 + 1))];
        var index = 0;

        for (var y = -radius; y <= radius; y++)
        for (var x = -radius; x <= radius; x++)
        {
            var tapX = (int)Math.Floor(centerX + x + 0.5);
            var tapY = (int)Math.Floor(centerY + y + 0.5);

            if (clampToTile)
            {
                tapX = Math.Clamp(tapX, tile.MinX, tile.MaxX);
                tapY = Math.Clamp(tapY, tile.MinY, tile.MaxY);
            }

            taps[index++] = new Tap(tapX, tapY);
        }

        return taps;
    }

    private static void Validate(
        Int2 atlasSize,
        TileRect tile,
        double localU,
        double localV,
        int radius)
    {
        if (atlasSize.X <= 0 || atlasSize.Y <= 0)
            throw new ArgumentOutOfRangeException(nameof(atlasSize));
        if (tile.Width <= 0 || tile.Height <= 0 || tile.MinX < 0 || tile.MinY < 0 ||
            tile.MaxX >= atlasSize.X || tile.MaxY >= atlasSize.Y)
            throw new ArgumentOutOfRangeException(nameof(tile));
        if (!double.IsFinite(localU) || !double.IsFinite(localV) ||
            localU < 0 || localU > 1 || localV < 0 || localV > 1)
            throw new ArgumentOutOfRangeException(nameof(localU));
        if (radius < 0 || radius > 8)
            throw new ArgumentOutOfRangeException(nameof(radius));
    }
}

$ dotnet restore ShadowAtlasPcfLab.csproj -p:NuGetAudit=false
$ dotnet build ShadowAtlasPcfLab.csproj -c Release --no-restore --nologo
$ dotnet run --project ShadowAtlasPcfLab.csproj -c Release --no-build

Build succeeded. 0 Warning(s), 0 Error(s)
PASS edge kernel crosses adjacent tile
PASS tile clamp keeps all taps in owner
PASS neighbor depth darkens naive visibility
PASS interior kernel remains unchanged
PASS invalid tile is rejected before sampling
PASS endpoints and one texel tile stay owned
PASS randomized reference agrees
tests=7 passed=7 failed=0 skipped=0 elapsedMs=216.390
randomCases=10000 disagreements=0
fixed naiveOutside=3 clampedOutside=0
fixed naiveVisibility=0.666667 clampedVisibility=1.000000
exitCode=0