drawlist -> own file

engine/drawlist.go

@@ -0,0 +1,34 @@
+package engine
+
+import "github.com/hajimehoshi/ebiten/v2"
+
+var _ Drawer = tombstone{}
+
+type tombstone struct{}
+
+func (tombstone) Draw(*ebiten.Image, *ebiten.DrawImageOptions) {}
+
+func (tombstone) DrawAfter(x Drawer) bool { return x != tombstone{} }
+func (tombstone) DrawBefore(Drawer) bool  { return false }
+
+type drawList struct {
+	list []Drawer
+	rev  map[Drawer]int
+}
+
+func (d drawList) Less(i, j int) bool {
+	if d.list[i] == (tombstone{}) {
+		return false
+	}
+	if d.list[j] == (tombstone{}) {
+		return true
+	}
+	return d.list[i].DrawBefore(d.list[j]) || d.list[j].DrawAfter(d.list[i])
+}
+
+func (d drawList) Len() int { return len(d.list) }
+
+func (d drawList) Swap(i, j int) {
+	d.rev[d.list[i]], d.rev[d.list[j]] = j, i
+	d.list[i], d.list[j] = d.list[j], d.list[i]
+}

engine/game.go

@@ -433,37 +433,6 @@ type abKey struct {
 	behaviour reflect.Type
 }
 
-var _ Drawer = tombstone{}
-
-type tombstone struct{}
-
-func (tombstone) Draw(*ebiten.Image, *ebiten.DrawImageOptions) {}
-
-func (tombstone) DrawAfter(x Drawer) bool { return x != tombstone{} }
-func (tombstone) DrawBefore(Drawer) bool  { return false }
-
-type drawList struct {
-	list []Drawer
-	rev  map[Drawer]int
-}
-
-func (d drawList) Less(i, j int) bool {
-	if d.list[i] == (tombstone{}) {
-		return false
-	}
-	if d.list[j] == (tombstone{}) {
-		return true
-	}
-	return d.list[i].DrawBefore(d.list[j]) || d.list[j].DrawAfter(d.list[i])
-}
-
-func (d drawList) Len() int { return len(d.list) }
-
-func (d drawList) Swap(i, j int) {
-	d.rev[d.list[i]], d.rev[d.list[j]] = j, i
-	d.list[i], d.list[j] = d.list[j], d.list[i]
-}
-
 // concatOpts returns the combined options (as though a was applied and then b).
 func concatOpts(a, b ebiten.DrawImageOptions) ebiten.DrawImageOptions {
 	a.ColorM.Concat(b.ColorM)