ichigo/engine/scene.go
2021-08-18 14:02:15 +10:00

85 lines
1.8 KiB
Go

package engine
import (
"encoding/gob"
"math"
"sort"
"github.com/hajimehoshi/ebiten/v2"
)
func init() {
gob.Register(Scene{})
}
// Scene manages drawing and updating a bunch of components.
type Scene struct {
Components []interface{}
Disabled bool
Hidden bool
ID
DrawOrder
}
// Draw draws all components in order.
func (s *Scene) Draw(screen *ebiten.Image, opts ebiten.DrawImageOptions) {
if s.Hidden {
return
}
for _, i := range s.Components {
if d, ok := i.(Drawer); ok {
d.Draw(screen, opts)
}
}
}
// Prepare does an initial Z-order sort.
func (s *Scene) Prepare(*Game) { s.sortByDrawOrder() }
// sortByDrawOrder sorts the components by Z position.
// Everything without a Z sorts first. Stable sort is used to avoid Z-fighting
// (among layers without a Z, or those with equal Z).
func (s *Scene) sortByDrawOrder() {
sort.SliceStable(s.Components, func(i, j int) bool {
a, aok := s.Components[i].(DrawOrderer)
b, bok := s.Components[j].(DrawOrderer)
if aok && bok {
return a.DrawOrder() < b.DrawOrder()
}
return !aok && bok
})
}
// Scan returns all immediate subcomponents.
func (s *Scene) Scan() []interface{} { return s.Components }
// Update calls Update on all Updater components.
func (s *Scene) Update() error {
if s.Disabled {
return nil
}
for _, c := range s.Components {
// Update each updater in turn
if u, ok := c.(Updater); ok {
if err := u.Update(); err != nil {
return err
}
}
}
// Check if the updates put the components out of order; if so, sort
cz := -math.MaxFloat64 // fun fact: this is min float64
for _, c := range s.Components {
z, ok := c.(DrawOrderer)
if !ok {
continue
}
if t := z.DrawOrder(); t > cz {
cz = t
continue
}
s.sortByDrawOrder()
return nil
}
return nil
}