feat: Replace FastAStarAlgorithm with BitmapAStarAlgorithm (#2446)

## Summary Replaces `FastAStarAlgorithm` with `BitmapAStarAlgorithm`: one cache lookup per cell expansion (8-direction mask + per-direction destination Z) instead of 8 separate `MovementImpl.CheckMovement` calls. Adds the supporting cache infrastructure to back it. Public API unchanged — `MovementPath` / `Mobile.Move` / `CalcMoves.Find` return the same shapes; the algorithm swap is internal. ## What's in this PR - **`BitmapAStarAlgorithm`** — A* that issues one `StepCache.TryGetMask` call per cell expansion. Inline fallthrough to the per-cell slow path for multi-Z, off-map, source-Z mismatch, and non-default walkers. - **`StepCache`** — singleton chunk store keyed by `(mapId, chunkX, chunkY)`. Lazily built on first query, invalidated by `Sector.MultisVersion` mismatch, memory-bounded by sampled probabilistic LRU. - **`StepProbe`** — computes static-only walkability for a single cell, mirroring `MovementImpl.Check` minus the item / mobile collision phases. - **`StepMask` / `StepChunk`** — value / storage types for the per-cell results. - **`CacheEvictionTimer`** — periodic cap backstop (60s interval; early-returns when not over cap). - **`Map.Sector.MultisVersion`** promoted to `public` so the cache can detect dynamic-static invalidations cheaply. ## Eviction strategy Sampled probabilistic LRU (Redis-style). Per eviction, sample 5 random keys from a parallel `List<long>` kept in lockstep with the chunk dictionary; evict the oldest of the sample via swap-and-pop. O(1) per eviction regardless of resident count, so sustained cap pressure has no perpetual perf hit. ## Capability handling (interim) Non-default walkers (non-GM players, creatures with `CanSwim` / `CanFly` / `CanOpenDoors` / `CanMoveOverObstacles`) route entirely through the per-cell slow path via `BitmapAStarAlgorithm.GetSuccessorsSlowPath`. The 2-pass design (cache + capability overlay + dynamic-obstacle pass) lands in the follow-up PR.
2026-05-05 21:53:43 -07:00 · 2026-05-05 21:53:43 -07:00 · 6a3804addc
commit 6a3804addc
parent ee1bf23b72
16 changed files with 1832 additions and 50 deletions
--- a/Projects/UOContent.Tests/Tests/Engines/Pathing/StepCacheParityTests.cs
+++ b/Projects/UOContent.Tests/Tests/Engines/Pathing/StepCacheParityTests.cs
@ -0,0 +1,90 @@
+using Server.Engines.Pathing.Cache;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Server.Tests.Pathfinding;
+
+[Collection("Sequential Pathfinding Tests")]
+public class StepCacheParityTests
+{
+    private readonly ITestOutputHelper _output;
+
+    public StepCacheParityTests(ITestOutputHelper output)
+    {
+        _output = output;
+    }
+
+    [Theory]
+    [InlineData("britain_inn_dense", 1480, 1610, 32)]
+    [InlineData("trammel_open_plain", 1500, 1600, 32)]
+    [InlineData("britain_causeway", 1475, 1641, 32)]
+    public void CacheMatchesBaker(string label, int xStart, int yStart, int size)
+    {
+        var cache = StepCache.Instance;
+        cache.Clear();
+
+        var map = Map.Maps[1];
+        Assert.NotNull(map);
+
+        var disagreements = 0;
+        var samples = 0;
+        var multiZ = 0;
+
+        for (var x = xStart; x < xStart + size; x++)
+        {
+            for (var y = yStart; y < yStart + size; y++)
+            {
+                map.GetAverageZ(x, y, out _, out var avgZ, out _);
+
+                // The cache bakes from the slow path's standing Z (the Z a creature actually
+                // stands at on this cell). Query with the same Z so the source-Z guard
+                // doesn't false-positive on every paver cell.
+                var sourceZ = (sbyte)StepProbe.ComputeStandingZ(map, x, y, avgZ);
+
+                var baker = StepProbe.ComputeMaskAt(map, x, y, sourceZ);
+
+                var ok = cache.TryGetMask(
+                    map, x, y, sourceZ,
+                    out var mask,
+                    out var dN, out var dNE, out var dE, out var dSE,
+                    out var dS, out var dSW, out var dW, out var dNW,
+                    out var hitKind
+                );
+
+                samples++;
+
+                if (hitKind == CacheHitKind.Fallthrough_MultiZ)
+                {
+                    multiZ++;
+                    continue;
+                }
+
+                Assert.True(ok, $"Cache returned !ok at ({x},{y}) hitKind={hitKind}");
+
+                if (mask != baker.Mask)
+                {
+                    disagreements++;
+                    _output.WriteLine($"MASK DIFF @ ({x},{y}) cache=0x{mask:X2} baker=0x{baker.Mask:X2}");
+                    continue;
+                }
+
+                if (dN != baker.DestZ_N || dNE != baker.DestZ_NE || dE != baker.DestZ_E || dSE != baker.DestZ_SE
+                    || dS != baker.DestZ_S || dSW != baker.DestZ_SW || dW != baker.DestZ_W || dNW != baker.DestZ_NW)
+                {
+                    disagreements++;
+                    _output.WriteLine($"Z DIFF @ ({x},{y}) cache=({dN},{dNE},{dE},{dSE},{dS},{dSW},{dW},{dNW}) baker=({baker.DestZ_N},{baker.DestZ_NE},{baker.DestZ_E},{baker.DestZ_SE},{baker.DestZ_S},{baker.DestZ_SW},{baker.DestZ_W},{baker.DestZ_NW})");
+                }
+            }
+        }
+
+        _output.WriteLine($"[{label}] samples={samples} disagreements={disagreements} multiZ={multiZ}");
+
+        // Non-vacuity: at least the inn region must have at least one cell that produced a real cache answer.
+        if (label == "britain_inn_dense")
+        {
+            Assert.True(samples - multiZ > 0, "expected real cache answers in dense region");
+        }
+
+        Assert.Equal(0, disagreements);
+    }
+}