Properly link flecs library

engine/libs/flecs/examples/cpp/observers/propagate/include/propagate.h

@@ -0,0 +1,16 @@
+#ifndef PROPAGATE_H
+#define PROPAGATE_H
+
+/* This generated file contains includes for project dependencies */
+#include "propagate/bake_config.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+

engine/libs/flecs/examples/cpp/observers/propagate/include/propagate/bake_config.h

@@ -0,0 +1,24 @@
+/*
+                                   )
+                                  (.)
+                                  .|.
+                                  | |
+                              _.--| |--._
+                           .-';  ;`-'& ; `&.
+                          \   &  ;    &   &_/
+                           |"""---...---"""|
+                           \ | | | | | | | /
+                            `---.|.|.|.---'
+
+ * This file is generated by bake.lang.c for your convenience. Headers of
+ * dependencies will automatically show up in this file. Include bake_config.h
+ * in your main project file. Do not edit! */
+
+#ifndef PROPAGATE_BAKE_CONFIG_H
+#define PROPAGATE_BAKE_CONFIG_H
+
+/* Headers of public dependencies */
+#include <flecs.h>
+
+#endif
+

engine/libs/flecs/examples/cpp/observers/propagate/project.json

@@ -0,0 +1,11 @@
+{
+    "id": "propagate",
+    "type": "application",
+    "value": {
+        "use": [
+            "flecs"
+        ],
+        "language": "c++",
+        "public": false
+    }
+}

engine/libs/flecs/examples/cpp/observers/propagate/src/main.cpp

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+#include <propagate.h>
+#include <iostream>
+
+// Events are propagated along relationship edges. This means that observers can
+// listen for events from a parent or prefab, like triggering when a component
+// inherited from a prefab was set.
+//
+// Event propagation happens automatically when an observer contains a filter
+// with the EcsUp flag set (indicating upwards traversal). Observers use the 
+// same matching logic as queries: if a query with upwards traversal matches an
+// entity, so will an observer.
+//
+// Events are only propagated along traversable relationship edges.
+
+struct Position {
+    double x, y;
+};
+
+int main(int, char *[]) {
+    flecs::world ecs;
+
+    // Create observer that listens for events from both self and parent
+    ecs.observer<Position, Position>()
+        .term_at(2).parent() // select 2nd Position from parent
+        .event(flecs::OnSet)
+        .each([](flecs::iter& it, size_t i, Position& p_self, Position& p_parent) {
+            std::cout << " - " << it.event().name() << ": " 
+                << it.event_id().str() << ": "
+                << it.entity(i).name() << ": "
+                << "self: {" << p_self.x << ", " << p_self.y << "}, "
+                << "parent: {" << p_parent.x << ", " << p_parent.y << "}\n";
+        });
+
+    // Create entity and parent
+    flecs::entity p = ecs.entity("p");
+    flecs::entity e = ecs.entity("e").child_of(p);
+
+    // Set Position on entity. This doesn't trigger the observer yet, since the
+    // parent doesn't have Position yet.
+    e.set<Position>({10, 20});
+
+    // Set Position on parent. This event will be propagated and trigger the 
+    // observer, as the observer query now matches.
+    p.set<Position>({1, 2});
+
+    // Output
+    //   - OnSet: Position: e: self: {10, 20}, parent: {1, 2}
+}