refactoring to systems complete. also added observers for collision checks

observers/particle_observer.go

@@ -0,0 +1,53 @@
+package observers
+
+import (
+	"github.com/mlange-42/arche/ecs"
+	"github.com/mlange-42/arche/ecs/event"
+	"github.com/mlange-42/arche/generic"
+	"github.com/mlange-42/arche/listener"
+)
+
+// will be added as  an ecs.Resource to the world so we  can use it in
+// CollisionSystem to dynamically make it appear or disappear
+type ParticleObserver struct {
+	// we only have one particle so far, if we use multiple ones, turn
+	// this in to a map, see player_observer.go for an example
+	Entity ecs.Entity
+}
+
+// Create a  new resource of  type PlayerObserver which will  hold all
+// player  entities.   We   also  add  a  Listener   which  looks  for
+// EntityRemoved events and  if a player gets removed,  we also remove
+// it from the Entity map in our observer.
+func NewParticleObserver(world *ecs.World) {
+	observer := &ParticleObserver{}
+
+	resmanger := generic.NewResource[ParticleObserver](world)
+	resmanger.Add(observer)
+
+	listen := listener.NewCallback(
+		func(world *ecs.World, event ecs.EntityEvent) {
+			observerID := ecs.ResourceID[ParticleObserver](world)
+			observer := world.Resources().Get(observerID).(*ParticleObserver)
+			observer.RemoveEntity(event.Entity)
+		},
+
+		event.EntityRemoved,
+	)
+
+	world.SetListener(&listen)
+}
+
+func GetParticleObserver(world *ecs.World) *ParticleObserver {
+	observerID := ecs.ResourceID[ParticleObserver](world)
+	observer := world.Resources().Get(observerID).(*ParticleObserver)
+	return observer
+}
+
+func (observer *ParticleObserver) AddEntity(entity ecs.Entity) {
+	observer.Entity = entity
+}
+
+func (observer *ParticleObserver) RemoveEntity(entity ecs.Entity) {
+	observer.Entity = ecs.Entity{}
+}

observers/player_observer.go

@@ -0,0 +1,52 @@
+package observers
+
+import (
+	"github.com/mlange-42/arche/ecs"
+	"github.com/mlange-42/arche/ecs/event"
+	"github.com/mlange-42/arche/generic"
+	"github.com/mlange-42/arche/listener"
+)
+
+// will be added as  an ecs.Resource to the world so we  can use it in
+// CollisionSystem  to check  for  player collisions.
+type PlayerObserver struct {
+	Entities map[ecs.Entity]int
+}
+
+// Create a  new resource of  type PlayerObserver which will  hold all
+// player  entities.   We   also  add  a  Listener   which  looks  for
+// EntityRemoved events and  if a player gets removed,  we also remove
+// it from the Entity map in our observer.
+func NewPlayerObserver(world *ecs.World) {
+	observer := &PlayerObserver{}
+	observer.Entities = make(map[ecs.Entity]int)
+
+	resmanger := generic.NewResource[PlayerObserver](world)
+	resmanger.Add(observer)
+
+	listen := listener.NewCallback(
+		func(world *ecs.World, event ecs.EntityEvent) {
+			observerID := ecs.ResourceID[PlayerObserver](world)
+			observer := world.Resources().Get(observerID).(*PlayerObserver)
+			observer.RemoveEntity(event.Entity)
+		},
+
+		event.EntityRemoved,
+	)
+
+	world.SetListener(&listen)
+}
+
+func GetPlayerObserver(world *ecs.World) *PlayerObserver {
+	observerID := ecs.ResourceID[PlayerObserver](world)
+	observer := world.Resources().Get(observerID).(*PlayerObserver)
+	return observer
+}
+
+func (observer *PlayerObserver) AddEntity(entity ecs.Entity) {
+	observer.Entities[entity] = 1
+}
+
+func (observer *PlayerObserver) RemoveEntity(entity ecs.Entity) {
+	delete(observer.Entities, entity)
+}