Add complete hierarchy and basics example

src/Flecs.NET.Examples/Cpp/Entities/Basics.cs

@@ -35,9 +35,16 @@
 alice.Remove<Walking>();
 
 // Iterate all entities with Position
-// ecs.each([](flecs::entity e, Position& p) {
-//     std::cout << e.name() << ": {" << p.x << ", " << p.y << "}" << "\n";
-// });
+using Filter filter = world.Filter(
+    filter: world.FilterBuilder().Term<Position>()
+);
+
+filter.Iter(it =>
+{
+    Column<Position> p = it.Field<Position>(1);
+    foreach (int i in it)
+        Console.WriteLine($"{it.Entity(i).Name()}: ({p[i].X}, {p[i].Y})");
+});
 
 public struct Position
 {
@@ -49,4 +56,10 @@ public struct Walking
 {
 }
 
+// Output
+// (10, 20)
+// [Position, Walking, (Identifier,Name)]
+// Alice: (10, 20)
+// Bob: (20, 30)
+
 #endif

src/Flecs.NET.Examples/Cpp/Entities/Hierarchy.cs

@@ -0,0 +1,68 @@
+#if Cpp_Entities_Hierarchy
+
+using Flecs.NET.Core;
+using static Flecs.NET.Bindings.Native;
+
+void IterateTree(Entity e, Position pParent = default)
+{
+    // Print hierarchical name of entity & the entity type
+    Console.WriteLine($"{e.Path()} [{e.Types().Str()}]");
+
+    // Get entity position
+    ref readonly Position p = ref e.Get<Position>();
+
+    // Calculate actual position
+    Position pActual = new() { X = p.X + pParent.X, Y = p.Y + pParent.Y };
+    Console.WriteLine($"({pActual.X}, {pActual.Y})\n");
+
+    // Iterate children recursively
+    e.Children(child => IterateTree(child, pActual));
+}
+
+using World world = World.Create();
+
+// Create a simple hierarchy.
+// Hierarchies use ECS relationships and the builtin flecs::ChildOf relationship to
+// create entities as children of other entities.
+
+Entity sun = world.Entity("Sun")
+    .Add<Star>()
+    .Set(new Position { X = 1, Y = 1 });
+
+world.Entity("Mercury")
+    .ChildOf(sun) // Shortcut for add(flecs::ChildOf, sun)
+    .Add<Planet>()
+    .Set(new Position { X = 1, Y = 1 });
+
+world.Entity("Venus")
+    .ChildOf(sun)
+    .Add<Planet>()
+    .Set(new Position { X = 2, Y = 2 });
+
+Entity earth = world.Entity("Earth")
+    .ChildOf(sun)
+    .Add<Planet>()
+    .Set(new Position { X = 3, Y = 3 });
+
+Entity moon = world.Entity("Moon")
+    .ChildOf(earth)
+    .Add<Moon>()
+    .Set(new Position { X = 0.1, Y = 0.1 });
+
+// Is the Moon a child of Earth?
+Console.WriteLine($"Child of Earth? {moon.Has(EcsChildOf, earth)}\n");
+
+// Do a depth-first walk of the tree
+IterateTree(sun);
+
+public struct Position
+{
+    public double X { get; set; }
+    public double Y { get; set; }
+}
+
+public struct Star { }
+public struct Planet { }
+public struct Moon { }
+
+#endif