71 lines
2.5 KiB
C++
71 lines
2.5 KiB
C++
#include <prefab.h>
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#include <iostream>
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// Prefabs are entities that can be used as templates for other entities. They
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// are created with a builtin Prefab tag, which by default excludes them from
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// queries and systems.
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struct Attack { double value; };
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struct Defense { double value; };
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struct FreightCapacity { double value; };
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struct ImpulseSpeed { double value; };
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struct HasFTL { };
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struct Position { double x = 0; double y = 0; };
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int main(int, char *[]) {
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flecs::world ecs;
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// Create a prefab hierarchy.
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flecs::entity spaceship = ecs.prefab("Spaceship")
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// Add components to prefab entity as usual
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.set<ImpulseSpeed>({50})
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.set<Defense>({50})
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// By default components in an inheritance hierarchy are shared between
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// entities. The override function ensures that instances have a private
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// copy of the component.
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.override<Position>();
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flecs::entity freighter = ecs.prefab("Freighter")
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// Short for .add(flecs::IsA, spaceship). This ensures the entity
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// inherits all components from spaceship.
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.is_a(spaceship)
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.add<HasFTL>()
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.set<FreightCapacity>({100})
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.set<Defense>({100});
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flecs::entity mammoth_freighter = ecs.prefab("MammothFreighter")
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.is_a(freighter)
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.set<FreightCapacity>({500})
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.set<Defense>({300});
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ecs.prefab("Frigate")
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.is_a(spaceship)
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.add<HasFTL>()
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.set<Attack>({100})
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.set<Defense>({75})
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.set<ImpulseSpeed>({125});
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// Create a regular entity from a prefab.
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// The instance will have a private copy of the Position component, because
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// of the override in the spaceship entity. All other components are shared.
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flecs::entity inst = ecs.entity("my_mammoth_freighter")
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.is_a(mammoth_freighter);
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// Inspect the type of the entity. This outputs:
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// Position,(Identifier,Name),(IsA,MammothFreighter)
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std::cout << "Instance type: [" << inst.type().str() << "]\n";
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// Even though the instance doesn't have a private copy of ImpulseSpeed, we
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// can still get it using the regular API (outputs 50)
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const ImpulseSpeed *ptr = inst.get<ImpulseSpeed>();
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std::cout << "Impulse speed: " << ptr->value << "\n";
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// Prefab components can be iterated just like regular components:
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ecs.each([](flecs::entity e, ImpulseSpeed& is, Position& p) {
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p.x += is.value;
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std::cout << e.name() << ": {" << p.x << ", " << p.y << "}\n";
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});
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}
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