118 lines
2.8 KiB
Go
118 lines
2.8 KiB
Go
package engine
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import (
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"encoding/gob"
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"io/fs"
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"github.com/hajimehoshi/ebiten/v2"
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)
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func init() {
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gob.Register(Game{})
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}
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// Game implements the ebiten methods using a collection of components.
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// One component must be the designated root component - usually a
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// scene of some kind.
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type Game struct {
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ScreenWidth int
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ScreenHeight int
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Root DrawUpdater // typically a *Scene or SceneRef though
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componentsByID map[string]interface{}
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}
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// Draw draws the entire thing, with default draw options.
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func (g *Game) Draw(screen *ebiten.Image) {
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g.Root.Draw(screen, ebiten.DrawImageOptions{})
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}
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// Layout returns the configured screen width/height.
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func (g *Game) Layout(outsideWidth, outsideHeight int) (w, h int) {
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return g.ScreenWidth, g.ScreenHeight
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}
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// Update updates the scene.
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func (g *Game) Update() error { return g.Root.Update() }
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// RegisterComponent tells the game there is a new component. Currently this is
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// only necessary for components with IDs.
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func (g *Game) RegisterComponent(c interface{}) {
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i, ok := c.(Identifier)
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if !ok {
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return
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}
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id := i.Ident()
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if id == "" {
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return
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}
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g.componentsByID[id] = c
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}
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// UnregisterComponent tells the game the component is no more.
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// Note this does not remove any references held by other components.
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func (g *Game) UnregisterComponent(c interface{}) {
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i, ok := c.(Identifier)
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if !ok {
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return
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}
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id := i.Ident()
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if id == "" {
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return
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}
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delete(g.componentsByID, id)
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}
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// Component returns the component with a given ID, or nil if there is none.
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func (g *Game) Component(id string) interface{} { return g.componentsByID[id] }
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// Scan implements Scanner.
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func (g *Game) Scan() []interface{} { return []interface{}{g.Root} }
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// Walk calls v with every component reachable from c via Scan, recursively,
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// for as long as visit returns nil.
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func Walk(c interface{}, v func(interface{}) error) error {
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if err := v(c); err != nil {
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return err
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}
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sc, ok := c.(Scanner)
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if !ok {
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return nil
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}
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for _, c := range sc.Scan() {
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if err := Walk(c, v); err != nil {
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return err
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}
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}
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return nil
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}
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// Load calls Load on all Loaders reachable via Scan (using Walk).
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// It stops on the first error.
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func (g *Game) Load(assets fs.FS) error {
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return Walk(g.Root, func(c interface{}) error {
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l, ok := c.(Loader)
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if !ok {
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return nil
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}
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return l.Load(assets)
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})
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}
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// Prepare builds the component database (using Walk) and then calls
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// Prepare on every Preparer. You must call Prepare before any calls
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// to Component. You may call Prepare again (e.g. as an alternative to
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// fastidiously calling RegisterComponent/UnregisterComponent).
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func (g *Game) Prepare() {
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g.componentsByID = make(map[string]interface{})
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Walk(g.Root, func(c interface{}) error {
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g.RegisterComponent(c)
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return nil
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})
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Walk(g.Root, func(c interface{}) error {
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if p, ok := c.(Prepper); ok {
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p.Prepare(g)
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}
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return nil
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})
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}
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