Tests - add Test_Tree_traverse() example

src/Tests/ECS/Entity/Test_Tree.cs

@@ -0,0 +1,48 @@
+using System.Numerics;
+using Friflo.Engine.ECS;
+using NUnit.Framework;
+using static NUnit.Framework.Assert;
+
+// ReSharper disable InconsistentNaming
+// ReSharper disable once CheckNamespace
+namespace Tests.ECS
+{
+public struct GlobalPosition : IComponent
+{
+    public Vector3 value;
+    public readonly override string ToString() => value.ToString();
+}
+
+public static class Test_Tree
+{
+
+    [Test]
+    public static void Test_Tree_traverse()
+    {
+        var store   = new EntityStore();
+        var root    = store.CreateEntity(new GlobalPosition());
+        var child1  = store.CreateEntity(new GlobalPosition(), new Position(5, 0, 0));
+        var child2  = store.CreateEntity(new GlobalPosition(), new Position(0, 3, 0));
+        root.AddChild(child1);
+        root.AddChild(child2);
+
+        TraverseHierarchy(root);
+
+        AreEqual(new Vector3(5,0,0), child1.GetComponent<GlobalPosition>().value);
+        AreEqual(new Vector3(0,3,0), child2.GetComponent<GlobalPosition>().value);
+    }
+
+    private static void TraverseHierarchy(Entity parent)
+    {
+        var parentGlobal = parent.GetComponent<GlobalPosition>().value;
+        foreach (var child in parent.ChildEntities) {
+            var data = child.Data;
+            if (!data.Has<Position>()) {
+                continue;
+            }
+            data.Get<GlobalPosition>().value = parentGlobal + data.Get<Position>().value;
+            TraverseHierarchy(child);
+        }
+    }
+}
+}