Properly link flecs library

engine/libs/flecs/examples/cpp/prefabs/slots/src/main.cpp

@@ -0,0 +1,65 @@
+#include <slots.h>
+#include <iostream>
+
+// Slots can be combined with prefab hierarchies to make it easier to access
+// the child entities created for an instance.
+//
+// To create a slot, the SlotOf relationship is added to the child of a prefab,
+// with as relationship target the prefab for which to register the slot. When
+// the prefab is instantiated, each slot will be added as a relationship pair
+// to the instance that looks like this:
+//   (PrefabChild, InstanceChild)
+//
+// For a SpaceShip prefab and an Engine child, that pair would look like this:
+//   (SpaceShip.Engine, Instance.Engine)
+//
+// To get the entity for a slot, an application can use the regular functions
+// to inspect relationships and relationship targets (see code).
+//
+// Slots can be added to any level of a prefab hierarchy, as long as it is above
+// (a parent of) the slot itself. When the prefab tree is instantiated, the 
+// slots are added to the entities that correspond with the prefab children.
+//
+// Without slots, an application would have to rely on manually looking up 
+// entities by name to get access to the instantiated children, like what the
+// hierarchy example does.
+
+int main() {
+    flecs::world ecs;
+
+    // Create the same prefab hierarchy as from the hierarchy example, but now
+    // with the SlotOf relationship.
+    flecs::entity SpaceShip = ecs.prefab("SpaceShip");
+        flecs::entity Engine = ecs.prefab("Engine")
+            .child_of(SpaceShip)
+            .slot_of(SpaceShip);
+
+        flecs::entity Cockpit = ecs.prefab("Cockpit")
+            .child_of(SpaceShip)
+            .slot_of(SpaceShip);
+
+    // Add an additional child to the Cockpit prefab to demonstrate how 
+    // slots can be different from the parent. This slot could have been
+    // added to the Cockpit prefab, but instead we register it on the top
+    // level SpaceShip prefab.
+    flecs::entity PilotSeat = ecs.prefab("PilotSeat")
+        .child_of(Cockpit)
+        .slot_of(SpaceShip);
+
+    // Create a prefab instance.
+    flecs::entity inst = ecs.entity("my_spaceship").is_a(SpaceShip);
+
+    // Get the instantiated entities for the prefab slots
+    flecs::entity inst_engine = inst.target(Engine);
+    flecs::entity inst_cockpit = inst.target(Cockpit);
+    flecs::entity inst_seat = inst.target(PilotSeat);
+    
+    std::cout << "instance engine:  " << inst_engine.path() << "\n";
+    std::cout << "instance cockpit: " << inst_cockpit.path() << "\n";
+    std::cout << "instance seat:    " << inst_seat.path() << "\n";
+
+    // Output:
+    //  instance engine:  ::my_spaceship::Engine
+    //  instance cockpit: ::my_spaceship::Cockpit
+    //  instance seat:    ::my_spaceship::Cockpit::PilotSeat
+}