Added Grid Units for asset placement.

Assets/Scripts/Grid Units.meta

@@ -0,0 +1,8 @@
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+guid: d181bf8b664de9e4cb7f81dad16d3f50
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
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Assets/Scripts/Grid Units/Grid.cs

@@ -0,0 +1,89 @@
+using Unity.Mathematics;
+using UnityEngine;
+using static Unity.Mathematics.math;
+using RigidTransform = Unity.Mathematics.RigidTransform;
+using quaternion = Unity.Mathematics.quaternion;
+
+public static class Grid
+{
+    
+    public static float CellSize = 0.25f;
+    public static float HalfCellSize => CellSize / 2;
+    
+    public static int3 ToSnappedDirection(this float3 direction)
+    {
+        float3 absDirection = abs(direction);
+        int axisIndex = absDirection.x >= absDirection.y
+            ? absDirection.x >= absDirection.z ? 0 : 2
+            : absDirection.y >= absDirection.z ? 1 : 2;
+
+        int3 snappedDirection = 0;
+        snappedDirection[axisIndex] = direction[axisIndex] > 0f ? 1 : -1;
+        return snappedDirection;
+    }
+    
+    public static int3x3 ToSnappedOrientation(this quaternion rotation)
+    {
+        float3x3 orientation = float3x3(rotation);
+
+        int3 snappedRight = ToSnappedDirection(orientation.c0);
+
+        int3 upMask = (int3)(snappedRight == 0);
+        int3 snappedUp = ToSnappedDirection(orientation.c1 * upMask);
+
+        int3 forwardMask = upMask * (int3)(snappedUp == 0);
+        int3 snappedForward = ToSnappedDirection(orientation.c2 * forwardMask);
+
+        return int3x3(snappedRight, snappedUp, snappedForward);
+    }
+
+    public static float3 ToMeters(int3 size) => (float3)size * HalfCellSize;
+    
+    private static RigidTransform GetParentSpace(Transform t)
+    {
+        Transform parent = t.parent;
+        GridUnit parentUnit = parent != null ? parent.GetComponentInParent<GridUnit>() : null;
+        if (parentUnit == null)
+        {
+            return RigidTransform.identity;
+        }
+
+        Transform parentTransform = parentUnit.transform;
+        RigidTransform parentSpace = RigidTransform(parentTransform.rotation, parentTransform.position);
+
+        float3 corner = parentUnit.CenterOffset - ToMeters(parentUnit.Size);
+        parentSpace.pos = transform(parentSpace, corner);
+        return parentSpace;
+    }
+    
+    public static void SnapUnit(Transform t, int3 size, float3 centerOffset)
+    {
+        RigidTransform parentSpace = GetParentSpace(t);
+
+        RigidTransform rt = RigidTransform(t.rotation, t.position);
+
+        rt = mul(inverse(parentSpace), rt);
+
+        int3x3 snappedOrientation = rt.rot.ToSnappedOrientation();
+        rt.rot = quaternion.LookRotation(snappedOrientation.c2, snappedOrientation.c1);
+
+        float3 nudge = float3(1f);
+        if (size.x % 2 == 0)
+            nudge += snappedOrientation.c0;
+        if (size.y % 2 == 0)
+            nudge += snappedOrientation.c1;
+        if (size.z % 2 == 0)
+            nudge += snappedOrientation.c2;
+        nudge *= 0.5f;
+
+        float3 centerOffsetW = mul(rt.rot, centerOffset);
+        float3 centerW = rt.pos + centerOffsetW;
+        centerW = (round(centerW / CellSize - nudge) + nudge) * CellSize;
+        rt.pos = centerW - centerOffsetW;
+
+        rt = mul(parentSpace, rt);
+
+        t.SetPositionAndRotation(rt.pos, rt.rot);
+    }
+
+}

Assets/Scripts/Grid Units/Grid.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 742f76c1bb9643469274cdb6fceee9ac
+timeCreated: 1723893723

Assets/Scripts/Grid Units/GridUnit.cs

@@ -0,0 +1,58 @@
+using UnityEngine;
+using UnityEditor;
+using Unity.Mathematics;
+using static Unity.Mathematics.math;
+using static Grid;
+using Color = UnityEngine.Color;
+
+#if UNITY_EDITOR
+
+[ExecuteAlways]
+[SelectionBase]
+[DisallowMultipleComponent]
+public class GridUnit : MonoBehaviour
+{
+    
+    public int3 Size = new (1, 1, 1);
+    private Vector3 SizeInMeters => new (Size.x * CellSize, Size.y * CellSize, Size.z * CellSize);
+    
+    public float3 CenterOffset;
+
+    [SerializeField, HideInInspector]
+    private int3 cachedSize = new (1, 1, 1);
+    [SerializeField, HideInInspector]
+    private float3 cachedOffset;
+    
+    private bool isDirty => transform.hasChanged || 
+                            !all(cachedOffset != CenterOffset) || 
+                            !all(cachedSize == Size);
+
+    public void Update()
+    {
+        if (!isDirty)
+        {
+            return;
+        }
+        
+        SnapUnit(transform, Size, CenterOffset);
+
+        transform.hasChanged = false;
+            
+        cachedOffset = CenterOffset;
+        cachedSize = Size;
+    }
+
+    [DrawGizmo(GizmoType.InSelectionHierarchy)]
+    private static void DrawGizmo(GridUnit unit, GizmoType type)
+    {
+        Transform t = unit.transform;
+        quaternion rotation = t.rotation;
+        var position = (float3)t.position + mul(rotation, unit.CenterOffset);
+        
+        Gizmos.color = Color.white;
+        Gizmos.matrix = Matrix4x4.TRS(position, rotation, Vector3.one);
+        Gizmos.DrawWireCube(Vector3.zero, unit.SizeInMeters);
+    }
+}
+
+#endif

Assets/Scripts/Grid Units/GridUnit.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: af3e57595c24e7b4dbb6f7f44db23525
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Packages/manifest.json

@@ -2,6 +2,7 @@
   "dependencies": {
     "com.unity.ide.rider": "3.0.31",
     "com.unity.ide.visualstudio": "2.0.22",
+    "com.unity.mathematics": "1.2.6",
     "com.unity.textmeshpro": "3.0.6",
     "com.unity.ugui": "1.0.0",
     "com.unity.modules.ai": "1.0.0",

Packages/packages-lock.json

@@ -25,6 +25,13 @@
       },
       "url": "https://packages.unity.com"
     },
+    "com.unity.mathematics": {
+      "version": "1.2.6",
+      "depth": 0,
+      "source": "registry",
+      "dependencies": {},
+      "url": "https://packages.unity.com"
+    },
     "com.unity.test-framework": {
       "version": "1.1.33",
       "depth": 1,