102 lines
3.7 KiB
C
102 lines
3.7 KiB
C
#include <variant.h>
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#include <stdio.h>
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/* Prefabs can inherit from each other, which creates prefab variants. With
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* variants applications can reuse a commmon set of components and specialize it
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* by adding or overriding components on the variant. */
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typedef struct { double value; } Attack;
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typedef struct { double value; } Defense;
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typedef struct { double value; } FreightCapacity;
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typedef struct { double value; } ImpulseSpeed;
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typedef struct {
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double x;
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double y;
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} Position;
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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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ECS_COMPONENT(ecs, Attack);
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ECS_COMPONENT(ecs, Defense);
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ECS_COMPONENT(ecs, FreightCapacity);
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ECS_COMPONENT(ecs, ImpulseSpeed);
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// Create a base prefab for SpaceShips.
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ecs_entity_t SpaceShip = ecs_new_prefab(ecs, "SpaceShip");
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ecs_set(ecs, SpaceShip, ImpulseSpeed, {50});
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ecs_set(ecs, SpaceShip, Defense, {25});
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// Create a Freighter variant which inherits from SpaceShip
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ecs_entity_t Freighter = ecs_new_prefab(ecs, "Freighter");
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ecs_add_pair(ecs, Freighter, EcsIsA, SpaceShip);
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ecs_set(ecs, Freighter, FreightCapacity, {100});
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ecs_set(ecs, Freighter, Defense, {50});
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// Create a MammothFreighter variant which inherits from Freighter
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ecs_entity_t MammothFreighter = ecs_new_prefab(ecs, "MammothFreighter");
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ecs_add_pair(ecs, MammothFreighter, EcsIsA, Freighter);
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ecs_set(ecs, MammothFreighter, FreightCapacity, {500});
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// Create a Frigate variant which inherits from SpaceShip
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ecs_entity_t Frigate = ecs_new_prefab(ecs, "Frigate");
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ecs_add_pair(ecs, Frigate, EcsIsA, SpaceShip);
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ecs_set(ecs, Frigate, Attack, {100});
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ecs_set(ecs, Frigate, Defense, {75});
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ecs_set(ecs, Frigate, ImpulseSpeed, {125});
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// Create an instance of the MammothFreighter. This entity will inherit the
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// ImpulseSpeed from SpaceShip, Defense from Freighter and FreightCapacity
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// from MammothFreighter.
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ecs_entity_t inst = ecs_new_entity(ecs, "my_freighter");
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ecs_add_pair(ecs, inst, EcsIsA, MammothFreighter);
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// Add a private Position component.
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ecs_set(ecs, inst, Position, {10, 20});
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// Instances can override inherited components to give them a private copy
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// of the component. This freighter got an armor upgrade:
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ecs_set(ecs, inst, Defense, {100});
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// Queries can match components from multiple levels of inheritance
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ecs_query_t *q = ecs_query(ecs, {
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.filter.terms = {
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{ .id = ecs_id(Position) },
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{ .id = ecs_id(ImpulseSpeed) },
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{ .id = ecs_id(Defense) },
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{ .id = ecs_id(FreightCapacity) }
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}
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});
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ecs_iter_t it = ecs_query_iter(ecs, q);
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while (ecs_query_next(&it)) {
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Position *p = ecs_field(&it, Position, 1);
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ImpulseSpeed *s = ecs_field(&it, ImpulseSpeed, 2);
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Defense *d = ecs_field(&it, Defense, 3);
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FreightCapacity *c = ecs_field(&it, FreightCapacity, 4);
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for (int i = 0; i < it.count; i ++) {
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printf("%s:\n", ecs_get_name(ecs, it.entities[i]));
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printf(" - position: %f, %f\n", p[i].x, p[i].y);
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printf(" - impulse speed: %f\n", s[i].value);
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printf(" - defense: %f\n", d[i].value);
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printf(" - capacity: %f\n", c[i].value);
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}
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}
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// Note that when matching tables with shared components, entities are
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// returned one by one. See the queries/instancing example for more details.
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// Output:
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// my_freighter:
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// - position: 10.000000, 20.000000
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// - impulse speed: 50.000000
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// - defense: 100.000000
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// - capacity: 500.000000
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return ecs_fini(ecs);
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}
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