ErrUnregister is a special error value which may be used to unregister a system from Draw or Update events.
var ErrUnregister = errors.New("unregister system")
func AddSystem(system System)
AddSystem registers a system to start receiving Update and Draw calls.
func CurrentDraws() int
CurrentDraws returns the number of System Draw calls required to draw the game on to the screen. Because entities may be handled by more than one System, this number may be higher than the number of active entities.
func CurrentEntities() int
CurrentEntities returns the number of currently active entities.
func CurrentUpdates() int
CurrentUpdates returns the number of System Update calls required to update the game state. Because entities may be handled by more than one System, this number may be higher than the number of active entities.
func Draw(screen *ebiten.Image) error
Draw draws the game on to the screen.
func Preallocate(entities int)
Preallocate creates and then immediately removes the specified number of entities. Because Gohan reuses removed entities, this has the effect of pre-allocating the memory used later to create entities normally. Pre-allocating enough entities to run your application after its systems has been added, but before any entities are created, will provide the greatest performance boost.
func Query(f interface{})
Query accepts any function which takes an entity and one or more components as arguments. The provided function will be called once for each matching entity. This function will block until the provided function returns.
func Reset()
Reset removes all entities, components and systems.
func Update() error
Update updates the game state.
Entity is an entity identifier.
type Entity int
func AllEntities() []Entity
AllEntities returns a slice of all active entities. To retrieve only the number of currently active entities, use CurrentEntities.
func NewEntity() Entity
NewEntity returns a new (or previously removed and cleared) Entity. Because Gohan reuses removed Entity IDs, a previously removed ID may be returned.
func (e Entity) AddComponent(component interface{})
AddComponent adds a Component to an Entity.
func (e Entity) Remove() bool
Remove removes the provided Entity's components, causing it to no longer be handled by any system. Because Gohan reuses removed EntityIDs, applications must also remove any internal references to the removed Entity.
func (e Entity) With(f interface{})
With accepts any function which takes one or more components as arguments. This function will block until the provided function returns.
System represents a system that runs continuously.
Systems may specify any number of required components by adding public fields to their struct. When no required components are specified, the system will run for every active entity.
While systems must implement the Update and Draw methods, the special error value ErrUnregister may be returned at any time by systems to indicate the method returning the error should not be called again.
Systems do not need to implement locking to prevent race conditions between Update and Draw methods. Ebitengine calls only one of these methods at a time.
type System interface {
// Update is called once for each matching Entity each time the game state is updated.
Update(e Entity) error
// Draw is called once for each matching Entity each time the game is drawn to the screen.
Draw(e Entity, screen *ebiten.Image) error
}