Properly link flecs library

engine/libs/flecs/examples/c/prefabs/nested_prefabs/src/main.c

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+#include <nested_prefabs.h>
+#include <stdio.h>
+
+// Nested prefabs make it possible to reuse an existing prefab inside another
+// prefab. An example of where this could be useful is a car with four wheels:
+// instead of defining four times what a wheel is a Car prefab can reference an 
+// existing Wheel prefab.
+//
+// Nested prefabs can be created by adding a child that is a variant (inherits 
+// from) another prefab. For more information on variants, see the variants
+// example.
+//
+// Instantiated children from a nested prefab still inherit from the original
+// prefab. The reason for this is that an instantiated child is an exact copy
+// of the prefab child, and the prefab child only has an IsA relationship to the
+// nested prefab.
+//
+// This example shows how auto overriding (see the auto override example) can be
+// used to give instantiated children from a nested prefab a private copy of an
+// inherited component.
+
+typedef struct {
+    double value;
+} TirePressure;
+
+int main(int argc, char *argv[]) {
+    ecs_world_t *ecs = ecs_init_w_args(argc, argv);
+
+    ECS_COMPONENT(ecs, TirePressure);
+
+    // Create a Wheel prefab, make sure each instantiated wheel has a private
+    // copy of the TirePressure component.
+    ecs_entity_t Wheel = ecs_new_prefab(ecs, "Wheel");
+    ecs_set(ecs, Wheel, TirePressure, { 32 });
+    ecs_override(ecs, Wheel, TirePressure);
+
+    // Create a Car prefab with four wheels. Note how the wheel names are
+    // prefixed with 'Car.', this is has the same effect as adding the
+    // (ChildOf, Car) relationship.
+    ecs_entity_t Car = ecs_new_prefab(ecs, "Car");
+        ecs_entity_t WheelFrontLeft = ecs_new_prefab(ecs, "Car.FrontLeft");
+        ecs_add_pair(ecs, WheelFrontLeft, EcsIsA, Wheel);
+
+        ecs_entity_t WheelFrontRight = ecs_new_prefab(ecs, "Car.FrontRight");
+        ecs_add_pair(ecs, WheelFrontRight, EcsIsA, Wheel);
+
+        ecs_entity_t WheelBackLeft = ecs_new_prefab(ecs, "Car.BackLeft");
+        ecs_add_pair(ecs, WheelBackLeft, EcsIsA, Wheel);
+
+        ecs_entity_t WheelBackRight = ecs_new_prefab(ecs, "Car.BackRight");
+        ecs_add_pair(ecs, WheelBackRight, EcsIsA, Wheel);
+
+    // Create a prefab instance.
+    ecs_entity_t inst = ecs_new_entity(ecs, "my_car");
+    ecs_add_pair(ecs, inst, EcsIsA, Car);
+
+    // Lookup one of the wheels
+    ecs_entity_t inst_front_left = ecs_lookup_child(ecs, inst, "FrontLeft");
+    
+    // The type shows that the child has a private copy of the TirePressure
+    // component, and an IsA relationship to the Wheel prefab.
+    char *type = ecs_type_str(ecs, ecs_get_type(ecs, inst_front_left));
+    printf("type: [%s]\n", type);
+    ecs_os_free(type);
+
+    // Get the TirePressure component & print its value
+    const TirePressure *p = ecs_get(ecs, inst_front_left, TirePressure);
+    printf("pressure: %f\n", p->value);
+
+    // Output
+    //  type: [TirePressure, (Identifier,Name), (ChildOf,my_car), (IsA,Wheel)]
+    //  pressure: 32.000000
+    
+    return ecs_fini(ecs);
+}