feat: 新增APNG支持，添加SaveToApng方法并更新main.go以处理APNG精灵。

main.go

@@ -149,6 +149,9 @@ func main() {
 	if err := board.SaveToGif("test.gif"); err != nil {
 		log.Fatal(err)
 	}
+	if err := board.SaveToApng("test.apng"); err != nil {
+		log.Fatal(err)
+	}
 	if err := board.SaveToWebp("test.webp"); err != nil {
 		log.Fatal(err)
 	}

sprite/named_sprite_board.go

@@ -12,6 +12,7 @@ import (
 	"sort"
 
 	"github.com/HugoSmits86/nativewebp"
+	"github.com/kettek/apng"
 )
 
 // 设置为true启用调试日志
@@ -959,3 +960,29 @@ func (b *NamedSpriteBoard) SaveToWebp(filename string) error {
 	}
 	return nil
 }
+
+func (b *NamedSpriteBoard) SaveToApng(filename string) error {
+	frames, delays := b.RenderToAnimatedImage()
+	if len(frames) == 0 {
+		return errors.New("no frames to save")
+	}
+	apngData := apng.APNG{
+		Frames: make([]apng.Frame, len(frames)),
+	}
+	for i, frame := range frames {
+		apngData.Frames[i] = apng.Frame{
+			Image:            frame,
+			DelayNumerator:   uint16(delays[i]),
+			DelayDenominator: 100,
+		}
+	}
+	f, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	if err := apng.Encode(f, apngData); err != nil {
+		return err
+	}
+	return nil
+}