Properly link flecs library

engine/libs/flecs/examples/c/systems/basics/src/main.c

@@ -0,0 +1,62 @@
+#include <basics.h>
+#include <stdio.h>
+
+typedef struct {
+    double x, y;
+} Position, Velocity;
+
+void Move(ecs_iter_t *it) {
+    Position *p = ecs_field(it, Position, 1);
+    const Velocity *v = ecs_field(it, Velocity, 2);
+
+    for (int i = 0; i < it->count; i ++) {
+        p[i].x += v[i].x;
+        p[i].y += v[i].y;
+        printf("%s: {%f, %f}\n", ecs_get_name(it->world, it->entities[i]), 
+            p[i].x, p[i].y);
+    }
+}
+
+int main(int argc, char *argv[]) {
+    ecs_world_t *ecs = ecs_init_w_args(argc, argv);
+
+    ECS_COMPONENT(ecs, Position);
+    ECS_COMPONENT(ecs, Velocity);
+
+    // Create a system for Position, Velocity.
+    ecs_entity_t move = ecs_system(ecs, {
+        // Systems are entities, and by initializing the .entity field we can
+        // set some additional properties for the system like a name. While this
+        // is not mandatory, it makes a system easier to find in tools like the
+        // explorer (https://www.flecs.dev/explorer/).
+        .entity = ecs_entity(ecs, {
+            .name = "Move" 
+        }),
+        .query.filter.terms = {
+            { .id = ecs_id(Position) },
+            { .id = ecs_id(Velocity), .inout = EcsIn }
+        },
+        .callback = Move
+    });
+
+    // C applications can also use the ECS_SYSTEM convenience macro:
+    // ECS_SYSTEM(ecs, Move, 0, Position, [in] Velocity);
+
+    // Create a few test entities for a Position, Velocity query
+    ecs_entity_t e1 = ecs_new_entity(ecs, "e1");
+    ecs_set(ecs, e1, Position, {10, 20});
+    ecs_set(ecs, e1, Velocity, {1, 2});
+
+    ecs_entity_t e2 = ecs_new_entity(ecs, "e2");
+    ecs_set(ecs, e2, Position, {10, 20});
+    ecs_set(ecs, e2, Velocity, {3, 4});
+
+    // This entity will not match as it does not have Position, Velocity
+    ecs_entity_t e3 = ecs_new_entity(ecs, "e3");
+    ecs_set(ecs, e3, Position, {10, 20});
+
+    // Run the system
+    ecs_run(ecs, move, 0.0f, NULL);
+
+    return ecs_fini(ecs);
+}