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I've hit a bit of a stumbling block in my quest to implement object cloning in my game engine. My goal is to have a cloning system that I don't have to maintain on a class by class basis, unless the class needs special treatment.

My game engine's setup revolves around a base class Object2D, which contains some image data in the form of a Texture2D. Well, the long story is that it contains a DisplayObject, which contains a Sprite, which contains a Texture2D. Naturally, other classes e.g. "Player", "Enemy", "Projectile", etc. all derive from the basic Object2D class.

Unfortunately, I found that XNA's Texture2D class isn't serializable. Which makes sense, as we wouldn't want to be duplicating texture data in memory all willy-nilly.

This creates a dilemma for me. I was using deep cloning methods to clone objects, but since it's not serializable I can no longer do that. I tried just marking the Texture2D [NonSerializable], but this causes problems when I try to draw, as the clone's texture is null. I wasn't able to find any hidden trick that allows me to assign it after cloning (like some sort of an "onClone()" method).

So I figured I'd do this. For objects that can't be deep cloned generically, I implement a "SpecialClone" interface that allows me to specify a clone() method.

However, because the class that can't be deep cloned generically is the base class, I'm right back where I started: writing a clone method on a class by class basis.

    public static T clone<T>(T obj) {
        if (obj == null) return default(T);

        if (!typeof(T).IsSerializable) {
            if (obj is SpecialClone) {
                object obj2 = ((SpecialClone)obj).clone();
                return (T)obj2;
            } else {
                throw new ArgumentException("Object type is not serializable.", "obj type: " + Type.GetTypeHandle(obj));
            }
        } else {
            return deepClone(obj);
        }
    }

    public static T deepClone<T>(T obj) {
        if (obj == null) return default(T);
        if (typeof(T).IsSerializable) {
            try {
                BinaryFormatter bf = new BinaryFormatter();
                MemoryStream ms = new MemoryStream();
                bf.Serialize(ms, obj);
                ms.Seek(0, SeekOrigin.Begin);
                T obj2 = (T)bf.Deserialize(ms);
                ms.Dispose();
                return obj2;
            }
            catch (Exception e) {
                Console.WriteLine(e);
                return default(T);
            }
        } else {
            Console.WriteLine(typeof(T) + " is not marked as serializable!");
            return default(T);
        }
    }

I'm not the best with C# yet, so I'm not sure if I'm missing some trick that I can use or if this is really how I'll have to deal with this problem. The main purpose of this cloning is for Object2D types, so it'd be a real pain to have to write clone methods for each new subclass I make.

Is there any way to avoid this?

Will Tice
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2 Answers2

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you do not want to clone the Texture2d.

You should consider Textures (and models, wave files, etc...) as a "shared asset", it could be many megabytes in size. Cloning that would leave you in a world of out-of-memory hurt real quick (in addition to the time it takes to clone)

your ideal solution: instead, you want to clone the reference.

if each of your Object2D instances are not meant to be serialized, then you can just reference-assign the same Texture2D to the various Object2D's. If you want to serialize, then pass the Texture2D reference, as mentioned, plus copy a string textureFilePath, which is what gets serialized.

Also note that this is what XNA's ContentManager does for you automatically: if you request "myPic.xnb" 10 times, it will automagically load it once and return that reference to you 10 times.

JasonS
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  • however, if you really, really wish to clone, then remember that Texture2D can be constructed from a stream, so you can use the static FromStream() method to "really" clone. http://msdn.microsoft.com/en-us/library/microsoft.xna.framework.graphics.texture2d.fromstream.aspx – JasonS Dec 26 '11 at 08:15
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ICloneable (.Net core interface) is better than SpecialClone. You could also implement the ISerializable interface allong with a protected constructor ctor(SerializationInfo info, StreamingContext context).

This would allow for custom serialization (SerializationInfo is a bag that can hold anything you need to deserialize the object later and is passed to you in the protected constructor).

So thats all there is to know about serialization. If you can do it or not depends on whether there is something in the non-serializable class (i.e. a key, a filename, a buffer) which you can use on deserialization to recreate that object.

John
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