Properly link flecs library

engine/libs/flecs/examples/cpp/systems/sync_point/src/main.cpp

@@ -0,0 +1,78 @@
+#include <sync_point.h>
+#include <iostream>
+
+struct Position { 
+    double x, y;
+};
+
+struct Velocity { 
+    double x, y;
+};
+
+int main(int, char *[]) {
+    flecs::world ecs;
+
+    // System that sets velocity using ecs_set for entities with Position.
+    // While systems are progressing, operations like ecs_set are deferred until
+    // it is safe to merge. By default this merge happens at the end of the
+    // frame, but we can annotate systems to give the scheduler more information
+    // about what it's doing, which allows it to insert sync points earlier.
+    //
+    // Note that sync points are never necessary/inserted for systems that write
+    // components provided by their signature, as these writes directly happen
+    // in the ECS storage and are never deferred.
+    //
+    // .inout_none() for Position tells the scheduler that while we 
+    // want to match entities with Position, we're not interested in reading or 
+    // writing the component value.
+    ecs.system("SetVelocity")
+        .with<Position>().inout_none()
+        .write<Velocity>() // Velocity is written, but shouldn't be matched
+        .each([](flecs::entity e) {
+            e.set<Velocity>({1, 2});
+        });
+
+    // This system reads Velocity, which causes the insertion of a sync point.
+    ecs.system<Position, const Velocity>("Move")
+        .each([](Position& p, const Velocity& v) {
+            p.x += v.x;
+            p.y += v.y;
+        });
+
+    // Print resulting Position
+    ecs.system<const Position>("PrintPosition")
+        .each([](flecs::entity e, const Position& p) {
+            std::cout << e.name() << ": {" << p.x << ", " << p.y << "}\n";
+        });
+
+    // Create a few test entities for a Position, Velocity query
+    ecs.entity("e1")
+        .set<Position>({10, 20})
+        .set<Velocity>({1, 2});
+
+    ecs.entity("e2")
+        .set<Position>({10, 20})
+        .set<Velocity>({3, 4});
+
+    // Run systems. Debug logging enables us to see the generated schedule
+    flecs::log::set_level(1);
+    ecs.progress();
+    flecs::log::set_level(-1); // Restore so we don't get world cleanup logs
+
+    // Output:
+    //  info: pipeline rebuild:
+    //  info: | schedule: threading: 0, staging: 1:
+    //  info: | | system SetVelocity
+    //  info: | | merge
+    //  info: | schedule: threading: 0, staging: 1:
+    //  info: | | system Move
+    //  info: | | system PrintPosition
+    //  info: | | merge
+    //  e1: {11.000000, 22.000000}
+    //  e2: {11.000000, 22.000000}
+    //
+    // The "merge" lines indicate sync points.
+    //
+    // Removing '.write<Velocity>()' from the system will remove the first
+    // sync point from the schedule.
+}