49 lines
1.7 KiB
C++
49 lines
1.7 KiB
C++
#include <propagate.h>
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#include <iostream>
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// Events are propagated along relationship edges. This means that observers can
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// listen for events from a parent or prefab, like triggering when a component
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// inherited from a prefab was set.
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//
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// Event propagation happens automatically when an observer contains a filter
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// with the EcsUp flag set (indicating upwards traversal). Observers use the
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// same matching logic as queries: if a query with upwards traversal matches an
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// entity, so will an observer.
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//
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// Events are only propagated along traversable relationship edges.
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struct Position {
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double x, y;
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};
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int main(int, char *[]) {
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flecs::world ecs;
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// Create observer that listens for events from both self and parent
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ecs.observer<Position, Position>()
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.term_at(2).parent() // select 2nd Position from parent
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.event(flecs::OnSet)
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.each([](flecs::iter& it, size_t i, Position& p_self, Position& p_parent) {
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std::cout << " - " << it.event().name() << ": "
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<< it.event_id().str() << ": "
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<< it.entity(i).name() << ": "
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<< "self: {" << p_self.x << ", " << p_self.y << "}, "
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<< "parent: {" << p_parent.x << ", " << p_parent.y << "}\n";
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});
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// Create entity and parent
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flecs::entity p = ecs.entity("p");
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flecs::entity e = ecs.entity("e").child_of(p);
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// Set Position on entity. This doesn't trigger the observer yet, since the
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// parent doesn't have Position yet.
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e.set<Position>({10, 20});
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// Set Position on parent. This event will be propagated and trigger the
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// observer, as the observer query now matches.
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p.set<Position>({1, 2});
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// Output
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// - OnSet: Position: e: self: {10, 20}, parent: {1, 2}
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}
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