Properly link flecs library

engine/libs/flecs/examples/cpp/queries/basics/src/main.cpp

@@ -0,0 +1,70 @@
+#include <basics.h>
+#include <iostream>
+
+struct Position { 
+    double x, y;
+};
+
+struct Velocity { 
+    double x, y;
+};
+
+int main(int, char *[]) {
+    flecs::world ecs;
+
+    // Create a query for Position, Velocity. Queries are the fastest way to
+    // iterate entities as they cache results.
+    flecs::query<Position, const Velocity> q = ecs.query<Position, const Velocity>();
+
+    // 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});
+
+    // This entity will not match as it does not have Position, Velocity
+    ecs.entity("e3")
+        .set<Position>({10, 20});
+
+
+    // The next lines show the different ways in which a query can be iterated.
+    // Note how the 'const' qualifier matches the query template arguments.
+
+    // The each() function iterates each entity individually and accepts an
+    // entity argument plus arguments for each query component:
+    q.each([](flecs::entity e, Position& p, const Velocity& v) {
+        p.x += v.x;
+        p.y += v.y;
+        std::cout << e.name() << ": {" << p.x << ", " << p.y << "}\n";
+    });
+
+    // You can omit the flecs::entity argument if it's not needed:
+    q.each([](Position& p, const Velocity& v) {
+        p.x += v.x;
+        p.y += v.y;
+        std::cout << "{" << p.x << ", " << p.y << "}\n";
+    });
+
+    // Each also accepts flecs::iter + index (for the iterated entity) arguemnts
+    // currently being iterated. A flecs::iter has lots of information on what
+    // is being iterated, which is demonstrated in the "iter" example.
+    q.each([](flecs::iter& it, size_t i, Position& p, const Velocity& v) {
+        p.x += v.x;
+        p.y += v.y;
+        std::cout << it.entity(i).name() << ": {" << p.x << ", " << p.y << "}\n";
+    });
+
+    // Iter is a bit more verbose, but allows for more control over how entities
+    // are iterated as it provides multiple entities in the same callback.
+    q.iter([](flecs::iter& it, Position *p, const Velocity *v) {
+        for (auto i : it) {
+            p[i].x += v[i].x;
+            p[i].y += v[i].y;
+            std::cout << it.entity(i).name() << 
+                ": {" << p[i].x << ", " << p[i].y << "}\n";
+        }
+    });
+}