78 lines
2.5 KiB
C
78 lines
2.5 KiB
C
#include <propagate.h>
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#include <stdio.h>
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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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typedef struct {
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double x, y;
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} Position;
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void Observer(ecs_iter_t *it) {
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ecs_world_t *ecs = it->world;
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// The event kind
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ecs_entity_t event = it->event;
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// The (component) id for which the event was emitted
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ecs_entity_t event_id = it->event_id;
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// Grab Position from self and parent
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Position *p_self = ecs_field(it, Position, 1);
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Position *p_parent = ecs_field(it, Position, 2);
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for (int i = 0; i < it->count; i ++) {
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ecs_entity_t e = it->entities[i];
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printf(" - %s: %s: %s: self: {%f, %f}, parent: {%f, %f}\n",
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ecs_get_name(ecs, event),
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ecs_get_name(ecs, event_id),
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ecs_get_name(ecs, e),
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p_self[i].x, p_self[i].y,
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p_parent[i].x, p_parent[i].y);
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}
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}
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int main(int argc, char *argv[]) {
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ecs_world_t *ecs = ecs_init_w_args(argc, argv);
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ECS_COMPONENT(ecs, Position);
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// Create observer that listens for events from both self and parent
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ecs_observer(ecs, {
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.filter = { .terms = {
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// Listen for Position events from self
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{ .id = ecs_id(Position) },
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// Listen for Position events from parent
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{ .id = ecs_id(Position), .src.flags = EcsUp, .src.trav = EcsChildOf }
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}},
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.events = { EcsOnSet },
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.callback = Observer
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});
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// Create entity and parent
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ecs_entity_t p = ecs_new_entity(ecs, "p");
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ecs_entity_t e = ecs_new_entity(ecs, "p.e"); // Create as 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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ecs_set(ecs, e, 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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ecs_set(ecs, p, Position, {1, 2});
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ecs_fini(ecs);
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// Output
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// - OnSet: Position: e: self: {10.000000, 20.000000}, parent: {1.000000, 2.000000}
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}
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