Properly link flecs library

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

@@ -0,0 +1,96 @@
+#include <hierarchies.h>
+#include <stdio.h>
+
+typedef struct {
+    double x;
+    double y;
+} Position;
+
+int main(int argc, char *argv[]) {
+    ecs_world_t *ecs = ecs_init_w_args(argc, argv);
+
+    ECS_COMPONENT(ecs, Position);
+
+    // Tags for local/ecs position
+    ECS_TAG(ecs, Local);
+    ECS_TAG(ecs, World);
+
+    // Create a hierarchy. For an explanation see the entities/hierarchy example
+    ecs_entity_t sun = ecs_new_entity(ecs, "Sun");
+    ecs_add_pair(ecs, sun, ecs_id(Position), World);
+    ecs_set_pair(ecs, sun, Position, Local, {1, 1});
+
+        ecs_entity_t mercury = ecs_new_entity(ecs, "Mercury");
+        ecs_add_pair(ecs, mercury, EcsChildOf, sun);
+        ecs_add_pair(ecs, mercury, ecs_id(Position), World);
+        ecs_set_pair(ecs, mercury, Position, Local, {1, 1});
+
+        ecs_entity_t venus = ecs_new_entity(ecs, "Venus");
+        ecs_add_pair(ecs, venus, EcsChildOf, sun);
+        ecs_add_pair(ecs, venus, ecs_id(Position), World);
+        ecs_set_pair(ecs, venus, Position, Local, {2, 2});
+
+        ecs_entity_t earth = ecs_new_entity(ecs, "Earth");
+        ecs_add_pair(ecs, earth, EcsChildOf, sun);
+        ecs_add_pair(ecs, earth, ecs_id(Position), World);
+        ecs_set_pair(ecs, earth, Position, Local, {3, 3});
+
+            ecs_entity_t moon = ecs_new_entity(ecs, "Moon");
+            ecs_add_pair(ecs, moon, EcsChildOf, earth);
+            ecs_add_pair(ecs, moon, ecs_id(Position), World);
+            ecs_set_pair(ecs, moon, Position, Local, {0.1, 0.1});
+
+    // Create a hierarchical query to compute the global position from the
+    // local position and the parent position.
+    ecs_query_t *q = ecs_query(ecs, {
+        .filter.terms = {
+            // Read from entity's Local position
+            { .id = ecs_pair(ecs_id(Position), Local), .inout = EcsIn }, 
+            // Write to entity's World position
+            { .id = ecs_pair(ecs_id(Position), World), .inout = EcsOut },
+
+            // Read from parent's World position
+            {
+                .id = ecs_pair(ecs_id(Position), World), 
+                .inout = EcsIn,
+                // Get from the parent, in breadth-first order (cascade)
+                .src.flags = EcsParent | EcsCascade,
+                // Make parent term optional so we also match the root (sun)
+                .oper = EcsOptional
+            }
+        }
+    });
+
+    // Do the transform
+    ecs_iter_t it = ecs_query_iter(ecs, q);
+    while (ecs_query_next(&it)) {
+        const Position *p = ecs_field(&it, Position, 1);
+        Position *p_out = ecs_field(&it, Position, 2);
+        const Position *p_parent = ecs_field(&it, Position, 3);
+        
+        // Inner loop, iterates entities in archetype
+        for (int i = 0; i < it.count; i ++) {
+            p_out[i].x = p[i].x;
+            p_out[i].y = p[i].y;
+            if (p_parent) {
+                p_out[i].x += p_parent->x;
+                p_out[i].y += p_parent->y;
+            }
+        }
+    }
+
+    // Print ecs positions
+    it = ecs_term_iter(ecs, &(ecs_term_t) {
+        .id = ecs_pair(ecs_id(Position), World)
+    });
+
+    while (ecs_term_next(&it)) {
+        Position *p = ecs_field(&it, Position, 1);
+        for (int i = 0; i < it.count; i ++) {
+            printf("%s: {%f, %f}\n", ecs_get_name(ecs, it.entities[i]),
+                p[i].x, p[i].y);
+        }
+    }
+
+    return ecs_fini(ecs);
+}