feat(core): add LandblockLoader with Stab+Building → WorldEntity mapping

src/AcDream.Core/World/LandblockLoader.cs

@@ -0,0 +1,77 @@
+using DatReaderWriter;
+using DatReaderWriter.DBObjs;
+
+namespace AcDream.Core.World;
+
+public static class LandblockLoader
+{
+    private const uint GfxObjMask = 0x01000000u;
+    private const uint SetupMask  = 0x02000000u;
+    private const uint TypeMask   = 0xFF000000u;
+
+    /// <summary>
+    /// Load a single landblock (heightmap + static objects) from the dats.
+    /// </summary>
+    /// <returns>Null if the landblock is missing from the cell dat.</returns>
+    public static LoadedLandblock? Load(DatCollection dats, uint landblockId)
+    {
+        var block = dats.Get<LandBlock>(landblockId);
+        if (block is null)
+            return null;
+
+        var info = dats.Get<LandBlockInfo>((landblockId & 0xFFFF0000u) | 0xFFFEu);
+        var entities = info is null
+            ? Array.Empty<WorldEntity>()
+            : BuildEntitiesFromInfo(info);
+
+        return new LoadedLandblock(landblockId, block, entities);
+    }
+
+    /// <summary>
+    /// Pure mapping from a parsed LandBlockInfo to a list of WorldEntity.
+    /// Each Stab and BuildingInfo becomes one entity. Unsupported id types
+    /// (neither GfxObj 0x01xxxxxx nor Setup 0x02xxxxxx) are silently skipped.
+    /// MeshRefs is left empty at this stage — Task 5 populates it.
+    /// </summary>
+    public static IReadOnlyList<WorldEntity> BuildEntitiesFromInfo(LandBlockInfo info)
+    {
+        var result = new List<WorldEntity>(info.Objects.Count + info.Buildings.Count);
+        uint nextId = 1;
+
+        foreach (var stab in info.Objects)
+        {
+            if (!IsSupported(stab.Id))
+                continue;
+            result.Add(new WorldEntity
+            {
+                Id = nextId++,
+                SourceGfxObjOrSetupId = stab.Id,
+                Position = stab.Frame.Origin,
+                Rotation = stab.Frame.Orientation,
+                MeshRefs = Array.Empty<MeshRef>(),
+            });
+        }
+
+        foreach (var building in info.Buildings)
+        {
+            if (!IsSupported(building.ModelId))
+                continue;
+            result.Add(new WorldEntity
+            {
+                Id = nextId++,
+                SourceGfxObjOrSetupId = building.ModelId,
+                Position = building.Frame.Origin,
+                Rotation = building.Frame.Orientation,
+                MeshRefs = Array.Empty<MeshRef>(),
+            });
+        }
+
+        return result;
+    }
+
+    private static bool IsSupported(uint id)
+    {
+        var type = id & TypeMask;
+        return type == GfxObjMask || type == SetupMask;
+    }
+}

src/AcDream.Core/World/LoadedLandblock.cs

@@ -0,0 +1,8 @@
+using DatReaderWriter.DBObjs;
+
+namespace AcDream.Core.World;
+
+public sealed record LoadedLandblock(
+    uint LandblockId,
+    LandBlock Heightmap,
+    IReadOnlyList<WorldEntity> Entities);

src/AcDream.Core/World/MeshRef.cs

@@ -0,0 +1,5 @@
+using System.Numerics;
+
+namespace AcDream.Core.World;
+
+public readonly record struct MeshRef(uint GfxObjId, Matrix4x4 PartTransform);

src/AcDream.Core/World/WorldEntity.cs

@@ -0,0 +1,12 @@
+using System.Numerics;
+
+namespace AcDream.Core.World;
+
+public sealed class WorldEntity
+{
+    public required uint Id { get; init; }
+    public required uint SourceGfxObjOrSetupId { get; init; }
+    public required Vector3 Position { get; init; }
+    public required Quaternion Rotation { get; init; }
+    public required IReadOnlyList<MeshRef> MeshRefs { get; init; }
+}