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feat(pathfinding): .swb format v8 compact index (#3b) (#2471)

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## Summary
Phase #3b (final roadmap item), stacked on #2470. Compacts the index trailer from 20 to 8 bytes/chunk.

Trammel: 19.2 MB → 17.9 MB. Roadmap total: 565 MB → 17.9 MB (−96.8%).

## Details
- Trailer stores `{ u32 packedKey = (ChunkX << 16) | ChunkY, u32 recordLength }` per chunk, in record write order; the file offset is dropped and reconstructed by cumulative recordLength from HeaderSize.
- No record reordering, no varint; fixed-stride, TryReadChunk unchanged.
- Also simplifies the accumulated `.swb` code comments across the stack.
- Format v8; v7 files rejected and re-baked once.

## Tests
v8 multi-chunk round-trip (cumulative offset reconstruction) + the v6/v7 suite; full pathfinding suite green; Release build clean.
This commit is contained in:
Kamron Batman 2026-06-07 01:22:20 -07:00 • committed by GitHub
parent c265bcbb5e
commit c7aaf33de9
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16 changed files with 960 additions and 868 deletions
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51
Projects/UOContent/Engines/Pathing/Cache/StepChunk.cs
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@ -4,17 +4,19 @@ namespace Server.Engines.Pathing.Cache;
/// <summary>
/// Per-chunk storage backing StepCache. Holds raw walk + swim masks and destination Z
/// values for each of 256 cells in a 16x16 chunk, plus build-time metadata (multis
/// version, multi-Z strata) and LRU bookkeeping.
/// values for each of 256 cells in a 16x16 chunk, plus build-time metadata (multis version, multi-Z strata)
/// and LRU bookkeeping.
/// </summary>
internal sealed class StepChunk
{
public const int CellsPerChunk = 256; // 16 x 16
/// <summary>Bit i of WalkMask[c] = "default walker can step from cell c to neighbor (Direction)i". Raw — no diagonal corner-cut applied here.</summary>
/// <summary>Bit i of WalkMask[c] = "default walker can step from cell c to neighbor (Direction)i".
/// Raw — no diagonal corner-cut applied here.</summary>
public readonly byte[] WalkMask = new byte[CellsPerChunk];
/// <summary>Bit i of WetMask[c] = "swim-only mob can step from cell c to neighbor (Direction)i". Layered with WalkMask via canSwim/cantWalk capability flags.</summary>
/// <summary>Bit i of WetMask[c] = "swim-only mob can step from cell c to neighbor (Direction)i".
/// Layered with WalkMask via canSwim/cantWalk capability flags.</summary>
public readonly byte[] WetMask = new byte[CellsPerChunk];
public readonly sbyte[] SourceZ = new sbyte[CellsPerChunk];
@ -103,25 +105,6 @@ internal sealed class StepChunk
}
}
/// <summary>Test/serialization hook: install pre-built swim-layer arrays. Pass nulls to clear.</summary>
internal void SetSwimLayer(
sbyte[] swimSourceZ, byte[] swimMask,
sbyte[] zN, sbyte[] zNE, sbyte[] zE, sbyte[] zSE,
sbyte[] zS, sbyte[] zSW, sbyte[] zW, sbyte[] zNW
)
{
_swimSourceZ = swimSourceZ;
_swimMask = swimMask;
_swimZN_extra = zN;
_swimZNE_extra = zNE;
_swimZE_extra = zE;
_swimZSE_extra = zSE;
_swimZS_extra = zS;
_swimZSW_extra = zSW;
_swimZW_extra = zW;
_swimZNW_extra = zNW;
}
/// <summary>Sentinel: cell has no strata — single-Z, use the main Walk/Wet arrays.</summary>
public const ushort NoStrata = ushort.MaxValue;
@ -151,8 +134,7 @@ internal sealed class StepChunk
public bool IsCellMultiZ(int cellIndex) => GetStrataOffset(cellIndex) != NoStrata;
public ushort GetStrataOffset(int cellIndex) =>
_strataOffsetByCell == null ? NoStrata : _strataOffsetByCell[cellIndex];
public ushort GetStrataOffset(int cellIndex) => _strataOffsetByCell == null ? NoStrata : _strataOffsetByCell[cellIndex];
public ReadOnlySpan<byte> StrataData =>
_strataData == null ? ReadOnlySpan<byte>.Empty : _strataData.AsSpan();
@ -182,18 +164,13 @@ internal sealed class StepChunk
/// record. Chunks with a swim layer (shore cells) are never uniform — their per-cell swim
/// data must be preserved via the Full record.
/// </summary>
internal bool IsUniform()
{
if (_strataOffsetByCell != null || HasSwimLayer)
{
return false;
}
return AllSame(WalkMask) && AllSame(WetMask) && AllSame(SourceZ)
&& AllSame(WalkZN) && AllSame(WalkZNE) && AllSame(WalkZE) && AllSame(WalkZSE)
&& AllSame(WalkZS) && AllSame(WalkZSW) && AllSame(WalkZW) && AllSame(WalkZNW)
&& AllSame(SwimZN) && AllSame(SwimZNE) && AllSame(SwimZE) && AllSame(SwimZSE)
&& AllSame(SwimZS) && AllSame(SwimZSW) && AllSame(SwimZW) && AllSame(SwimZNW);
}
internal bool IsUniform() => _strataOffsetByCell == null
&& !HasSwimLayer
&& AllSame(WalkMask) && AllSame(WetMask) && AllSame(SourceZ)
&& AllSame(WalkZN) && AllSame(WalkZNE) && AllSame(WalkZE) && AllSame(WalkZSE)
&& AllSame(WalkZS) && AllSame(WalkZSW) && AllSame(WalkZW) && AllSame(WalkZNW)
&& AllSame(SwimZN) && AllSame(SwimZNE) && AllSame(SwimZE) && AllSame(SwimZSE)
&& AllSame(SwimZS) && AllSame(SwimZSW) && AllSame(SwimZW) && AllSame(SwimZNW);
// "All 256 cells equal" via SIMD-accelerated ContainsAnyExcept (skip cell 0, the reference).
private static bool AllSame(byte[] a) => a.Length < 2 || !a.AsSpan(1).ContainsAnyExcept(a[0]);