Added Grid Units for asset placement.

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