Properly link flecs library

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

@@ -0,0 +1,85 @@
+#include <basics.h>
+#include <stdio.h>
+
+typedef struct {
+    double x;
+    double y;
+} Position, Velocity;
+
+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 query for Position, Velocity. Queries are the fastest way to
+    // iterate entities as they cache results.
+    ecs_query_t *q = ecs_query(ecs, {
+        .filter.terms = {
+            { .id = ecs_id(Position) }, 
+            { .id = ecs_id(Velocity), .inout = EcsIn}
+        }
+    });
+
+    // 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});
+
+    // Iterate entities matching the query
+    ecs_iter_t it = ecs_query_iter(ecs, q);
+
+    // Outer loop, iterates archetypes
+    while (ecs_query_next(&it)) {
+        Position *p = ecs_field(&it, Position, 1);
+        const Velocity *v = ecs_field(&it, Velocity, 2);
+
+        // Inner loop, iterates entities in archetype
+        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(ecs, it.entities[i]), 
+                p[i].x, p[i].y);
+        }
+    }
+
+    // Filters are uncached queries. They are a bit slower to iterate but faster
+    // to create & have lower overhead as they don't have to maintain a cache.
+    ecs_filter_t *f = ecs_filter(ecs, {
+        .terms = {
+            { .id = ecs_id(Position) }, 
+            { .id = ecs_id(Velocity), .inout = EcsIn}
+        }
+    });
+
+    // Filter iteration looks the same as query iteration
+    it = ecs_filter_iter(ecs, f);
+
+    while (ecs_filter_next(&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(ecs, it.entities[i]), 
+                p[i].x, p[i].y);
+        }
+    }
+
+    // Cleanup filter. Filters can allocate memory if the number of terms 
+    // exceeds their internal buffer, or when terms have names. In this case the
+    // filter didn't allocate, so while fini isn't strictly necessary here, it's
+    // still good practice to add it.
+    ecs_filter_fini(f);
+
+    return ecs_fini(ecs);
+}