rearrange Unregister

engine/container.go

@@ -135,11 +135,13 @@ func (c *Container) Register(component, parent interface{}) error {
 // to nil. If the number of nil items is greater than half the slice, the slice
 // is compacted.
 func (c *Container) Unregister(component interface{}) {
-	if i, found := c.reverse[component]; found {
+	i, found := c.reverse[component]
+	if !found {
+		return
+	}
 	c.items[i] = nil
 	c.free[i] = struct{}{}
 	delete(c.reverse, i)
-	}
 	if len(c.free) > len(c.items)/2 {
 		c.compact()
 	}

engine/drawdag.go

@@ -1,6 +1,7 @@
 package engine
 
 import (
+	"encoding/gob"
 	"fmt"
 	"image"
 	"log"
@@ -21,6 +22,10 @@ var _ interface {
 	Updater
 } = &DrawDAG{}
 
+func init() {
+	gob.Register(&DrawDAG{})
+}
+
 // DrawDAG is a DrawLayer that organises DrawBoxer descendants in a directed
 // acyclic graph (DAG), in order to draw them according to ordering constraints.
 // It combines a DAG with a spatial index used when updating vertices to reduce

engine/drawdfs.go

@@ -1,6 +1,10 @@
 package engine
 
-import "github.com/hajimehoshi/ebiten/v2"
+import (
+	"encoding/gob"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
 
 var _ interface {
 	Drawer
@@ -8,6 +12,10 @@ var _ interface {
 	Scanner
 } = &DrawDFS{}
 
+func init() {
+	gob.Register(&DrawDFS{})
+}
+
 // DrawDFS is a DrawLayer that does not add any structure. Components are
 // drawn in the order in which they are encountered by a depth-first search
 // through the game tree, without any extra sorting based on Z values or