Properly link flecs library

engine/libs/flecs/examples/c/hello_world/src/main.c

@@ -0,0 +1,64 @@
+#include <hello_world.h>
+#include <stdio.h>
+
+typedef struct {
+    double x;
+    double y;
+} Position, Velocity;
+
+/* Move system implementation. System callbacks may be called multiple times,
+ * as entities are grouped in tables by which components they have, and each 
+ * table has its own set of component arrays. */
+void Move(ecs_iter_t *it) {
+    Position *p = ecs_field(it, Position, 1);
+    Velocity *v = ecs_field(it, Velocity, 2);
+
+    /* Print the set of components for the iterated over entities */
+    char *type_str = ecs_table_str(it->world, it->table);
+    printf("Move entities with [%s]\n", type_str);
+    ecs_os_free(type_str);
+
+    /* Iterate entities for the current table */
+    for (int i = 0; i < it->count; i ++) {
+        p[i].x += v[i].x;
+        p[i].y += v[i].y;
+    }
+}
+
+int main(int argc, char *argv[]) {
+    /* Create the world */
+    ecs_world_t *world = ecs_init_w_args(argc, argv);
+
+    /* Register components */
+    ECS_COMPONENT(world, Position);
+    ECS_COMPONENT(world, Velocity);
+
+    /* Register system */
+    ECS_SYSTEM(world, Move, EcsOnUpdate, Position, Velocity);
+
+    /* Register tags (components without a size) */
+    ECS_TAG(world, Eats);
+    ECS_TAG(world, Apples);
+    ECS_TAG(world, Pears);
+
+    /* Create an entity with name Bob, add Position and food preference */
+    ecs_entity_t Bob = ecs_new_entity(world, "Bob");
+    ecs_set(world, Bob, Position, {0, 0});
+    ecs_set(world, Bob, Velocity, {1, 2});
+    ecs_add_pair(world, Bob, Eats, Apples);
+
+    /* Run systems twice. Usually this function is called once per frame */
+    ecs_progress(world, 0);
+    ecs_progress(world, 0);
+
+    /* See if Bob has moved (he has) */
+    const Position *p = ecs_get(world, Bob, Position);
+    printf("Bob's position is {%f, %f}\n", p->x, p->y);
+
+    return ecs_fini(world);
+
+    // Output
+    //  Move entities with [Position, Velocity, (Identifier,Name), (Eats,Apples)]
+    //  Move entities with [Position, Velocity, (Identifier,Name), (Eats,Apples)]
+    //  Bob's position is {2.000000, 4.000000}
+}