How you can Reverse Engineer a Unity Sport

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On this tutorial you’ll use ILSpy and AssetStudio to extract code and property from a compiled Unity sport.

Within the context of software program, reverse engineering is the follow of analyzing a system to extract design and implementation info. That is typically used to higher perceive how software program capabilities. One technique of reverse engineering is decompiling, which performs the other operations of a compiler to transform executable packages again into human-readable code.

You’ll be able to decompile Unity video games utilizing specialised instruments to extract the code and most property. Listed below are some widespread use circumstances the place this may be helpful:

  • Recuperate the misplaced code and property of a sport you made.
  • Check out the supply code or 3D fashions of a sport to review and study from.
  • Mod a sport by changing property with your personal.

Notice: With nice energy comes nice accountability. The reverse engineering methods described on this tutorial are meant for authorized use circumstances like recovering initiatives you made your self or for instructional use. Stealing code and property and claiming them as your personal is illegitimate and I’m not chargeable for any authorized penalties.

On this tutorial, you’ll use ILSpy and AssetStudio to decompile a Unity sport on Home windows. Alongside the way in which, you’ll discover ways to:

  • Use ILSpy to decompile a sport’s code
  • Save the code to your pc
  • Examine property utilizing AssetStudio
  • Extract audio and 3D fashions from a sport

Whereas I’ll be protecting Home windows functions on this tutorial, there are options for Linux and macOS on the market with the identical performance like AvaloniaILSpy and UnityPy. I’ve additionally added some extra software program issues on the backside of the tutorial, a few of that are cross-platform.

Getting Began

Click on the Obtain Supplies button on the prime or backside of this web page to obtain the pattern sport, Avoiding Duty. Extract the zip file to a folder to be used in a while. In order for you, you’ll be able to play the sport on Home windows by working Avoiding Duty.exe. You’ll be able to stop the sport by urgent Escape or Alt + F4.

Screenshot of a game in which a grey cutout of a man moves on a wooden stage while red crystals are shattering into pieces.

Granted, there’s not a lot happening aside from some crimson “accountability” crystals falling down from above whereas a cheery tune performs within the background. It gained’t be the sport of the 12 months anytime quickly, however that’s not the main focus of this tutorial. Within the following sections, you’ll choose this sport aside to entry its supply code and property.

Software necessities

On to the instruments! Each ILSpy and AssetStudio want the .NET 6 SDK to work. To test if you have already got this SDK put in, open a Command Immediate by opening the Begin menu, coming into “cmd” and urgent Enter. With the Command Immediate open, enter the next command and press Enter to execute it:

dotnet --list-sdks

When you’ve got .NET 6 SDK put in, there must be a 6.X.X entry within the record:

A command line interface showing 6.0.400

If there’s no 6.X.X entry, otherwise you get an “dotnet is just not acknowledged” error, you’ll want to put in the newest model of the SDK from right here: https://dotnet.microsoft.com/en-us/obtain/dotnet/6.0
Select the installer model that matches your CPU’s structure and obtain it. In most fashionable techniques, this shall be x64:

Windows x64 is highlighted

Now set up the SDK and re-run the dotnet --list-sdks command in a Command Immediate to confirm it’s put in.

Downloading ILSpy and AssetStudio

With the necessities out of the way in which, head over to the releases web page of ILSpy: https://github.com/icsharpcode/ILSpy/releases

Click on on the Belongings button on the backside of the changelog of the newest launch and click on on the ILSpy_selfcontained_x64 zip to obtain it.

ILSpy_selfcontained_x64

As soon as the obtain finishes, extract the zip to a folder to be used within the subsequent part.

Subsequent up is AssetStudio, the obtain course of right here is just like IlSpy. To start out off, head over to the releases web page: https://github.com/Perfare/AssetStudio/releases

Click on the Belongings button if the property aren’t seen immediately and click on on the .net6 hyperlink to obtain the .NET 6 model of AssetStudio.

AssetStudio.net6

Extract the contents of the zip to a folder for later use.

Extracting Supply Code

To extract the code from the pattern sport, you’ll want to make use of ILSpy, which is a an open-source .NET meeting browser and decompiler. Unity video games use C# for his or her scripts, which get compiled to Intermediate Language, or IL for brief. IL is a decrease degree language than C#, however nonetheless larger degree than machine code. Right here’s what IL code appears to be like like:

.technique public hidebysig static void Fundamental() il managed
{
    .entrypoint
    // Code dimension    11 (0xb)
    .maxstack 8
    IL_0000:         ldstr     "Hiya, World"
    IL_0005:    name void [mscorlib]System.Console::WriteLine
                         (class System.String)
} // finish of technique HelloWorld::Fundamental

By default, Unity compiles all scripts collectively right into a single file named Meeting-CSharp.dll. As a Unity developer, you’ll be able to select to group scripts in extra meeting definitions recordsdata, which can generate further meeting recordsdata when you compile your sport. ILSpy can learn the IL code in these recordsdata and convert them again to C# lessons.

Time to try what IlSpy presents! Open the ILSpy folder and double click on on ILSpy.exe to start out ILSpy. In case your necessities are so as, that is what you’ll see as soon as the applying masses:

The interface of ILSpy

Exploring ILSpy

The interface is cut up up into two major sections: an inventory of loaded assemblies on the left and the decompiled C# code on the appropriate. ILSpy has some generally used .NET assemblies loaded by default like mscorelib and System.

To load the pattern sport’s CSharp meeting, click on on the folder icon within the menu bar or press CTRL + O in your keyboard to open a folder browser window.

The open button of ILSpy

Navigate to the Avoiding Duty folder you unzipped earlier, there must be a file named Avoiding Duty.exe in there. From there, navigate to the Information folder, named Avoiding Responsibility_Data on this case and open the Managed folder in there. In brief: Sport folder / Information / Managed.

You need to see an inventory of DLL recordsdata in there.

A file named Assembly-CSharp.dll

Double-click Meeting-CSharp.dll to load the meeting in ILSpy. If all went nicely, a brand new entry was added within the Assemblies record on the left named Meeting-CSharp.

To examine the meeting, click on on the little + button on the left of the entry to broaden the meeting. This unveils the next objects:

  • Metadata: This comprises info on the meeting, together with its headers and strings.
  • References: An inventory of different assemblies this meeting references. ILSpy will routinely load in these assemblies if you’re inspecting code that references them, so don’t be shocked if the Assemblies record will get crammed up with extra assemblies.
  • A “-” namespace: The pattern sport doesn’t use namespaces in its code, however different initiatives can have an inventory right here of the totally different namespaces used. That is the place the supply code lives.

Increase the - namespace to get your first glimpse of one thing acquainted — an inventory of lessons! Subsequent, click on on the Rotate class and also you’ll see the supply code being proven on the appropriate.

A Rotate class

You’ll have to click on the + buttons within the code to broaden the strategies, nevertheless it’s all proper there:

Source code of the Rotate class

Exporting Code

It can save you the code by copy-pasting it right into a file, or by right-clicking the category within the Assemblies record and deciding on Save Code… within the menu. Now you can select a location to save lots of the C# file to. Don’t fear, you’re free to repeat my wonderful code and use it in your personal. :]

Save Code... entry in a menu

In giant assemblies, having to examine and save the lessons individually can get tedious, so I’ll introduce you to a extra environment friendly approach of saving the code. Proper-click on Meeting-CSharp and select Save Code… within the menu. It will immediate you to decide on a location to save lots of the C# mission file to. It would appear to be you’re saving a single file right here, however ILSpy will really copy over all lessons it may discover as C# recordsdata, together with a mission file.

CS files in a folder

Typically, ILSpy does a fairly good job of decompiling the code, however it’s possible you’ll run into some bizarre code right here and there if the decompiler wasn’t certain what to do. For example, in the event you check out the BrokenResponsibility class, it has a DestroySelf technique which differs from the unique code. The decompiled model appears to be like like this:

non-public void DestroySelf()
{
  Object.Destroy(base.gameObject);
}

Whereas the unique code was the next:

non-public void DestroySelf()
{
  Destroy(gameObject);
}

Notice the Object class and base key phrase that had been added to the tactic name. The decompiled code continues to be legitimate, however you may wish to think about cleansing it up a bit when utilizing it in your personal initiatives.

That concludes using ILSpy! It’s a robust instrument to bear in mind when that you must extract the supply code from Unity video games and different .NET based mostly merchandise. It has saved me a number of instances already once I misplaced my initiatives because of knowledge corruption. Backups are higher in each approach, however this can be a good backup. Simply keep in mind to be good and use it for good solely.

Now you know the way to examine and save supply code, it’s time to maneuver on to extracting the property.

Extracting Belongings

AssetStudio is an open-source instrument that may examine and extract the next asset sorts from Unity 3.4 to 2022.1:

  • Textures and sprites
  • Audio
  • Fonts
  • Meshes
  • Textual content
  • Shaders
  • Video recordsdata
  • Animations

It does this by reverse engineering the packed codecs and changing these again into usable codecs. A texture for instance could be transformed into png, tga, jpeg or bmp.

Open AssetStudio by opening the folder you extracted within the Getting Began part and double-click AssetStudioGUI.exe. After a short time, you’ll be greeted by its consumer interface:

AssetStudio interface

Tour of AssetStudio

Like ILSpy, AssetStudio has two major sections: a file browser on the left and a preview on the appropriate. In contrast to ILSpy nevertheless, there’s nothing to see right here till you open an property file or a folder of a compiled sport.
Earlier than delving deeper within the software, disable all error messages as on the time of writing AssetStudio has some points with loading in shaders, leading to a ton of errors being generated. To disregard these, choose Debug within the toolbar and uncheck Present error message.

Debug, Show error message

Now load within the property by deciding on File ▸ Load folder within the toolbar to open a folder browser window.

Load folder menu entry

Navigate to the Avoiding Duty folder, you already know you’re on the proper place in the event you see the Avoiding Responsibility_Data folder:

The Data and MonoBleedingEdge folders

Choose this folder to load it. AssetStudio will now search all subfolders for any asset recordsdata and browse their contents. This may take fairly some time relying on the quantity of property and their sort. So long as the progress bar on the backside is transferring and the textual content discipline beneath the preview reads “Learn property…” you ought to be good. It took my system about two minutes earlier than the applying was lastly carried out loading.

As soon as the property are loaded, it’s best to see an inventory of scenes and prefabs showing within the Scene Hierarchy tab:

level0 and sharedassets0.assets

You’ll be able to broaden these to get a tough concept of what kind of GameObjects make up the scene, however aside from that it’s not that helpful.

A hierachy of objects of a scene

Exporting Belongings

Open the Asset Record tab, as that’s the place the enjoyable begins. In right here, yow will discover all property supported by AssetStudio which are a part of the pattern sport. Most of those are included by Unity, however some had been added by me when creating the sport.

A list of assets

The record could be filtered by title if you already know what to search for through the use of the textbox beneath the tabs. For instance, sort in “Entertainer” and wait a short time, the record will shrink all the way down to a single AudioClip of the background music.

A single asset highlighted named Entertainer

Preview the file by clicking on its title within the Asset Record and urgent the Play button within the Preview window on the appropriate.

A button labelled Play

Click on on the Cease button when you’re carried out having fun with the tune. It can save you this asset by right-clicking its title and deciding on Export chosen property within the menu. It will immediate you to decide on a folder to reserve it to.

Notice: The music is “The Entertainer” by Kevin MacLeod (incompetech.com). It’s licensed underneath the Artistic Commons: By Attribution 4.0 License.

Export selected assets is highlighted in a menu

AssetStudio will create a folder based mostly on the kind of asset, AudioClip on this case. Inside you’ll discover the audio file in WAV format.

The Entertainer.wav

Filter out the filter by deciding on the textual content you’ve added and hitting Backspace or Delete in your keyboard. There’s one other technique to filter property: by their sort.

Choose Filter Sort ▸ Mesh within the toolbar to solely present 3D fashions within the record. The fashions used within the pattern sport all have the identical title: default. You’ll be able to choose them one after the other to get a pleasant preview.

Now choose all default meshes, right-click on any of them and choose Export chosen Belongings within the menu. Choose a folder to save lots of the fashions to within the folder browser window like earlier than.

As soon as the fashions are exported, they’re all in OBJ format. You need to use an software like Blender to import these recordsdata, edit them and export to a format of your selecting. You may as well use them as-is, as most sport engines assist OBJ meshes.

OBJ files in a folder

Right here’s the default.obj file opened up in Blender for example:

A 3D model of a stage

That’s it for AssetStudio, one other tremendous instrument to have in your arsenal.

The place to Go From Right here?

Congratulations on ending this tutorial! You now know how you can extract the supply code and property out of a compiled Unity sport. I sincerely hope these methods will show as helpful for you as they did for me.

You’ll be able to obtain the pattern sport utilizing the Obtain Supplies button on the prime or backside of this tutorial if you wish to mess around with it some extra.
If you wish to check out another instruments to reverse engineer Unity video games, listed here are my suggestions:

  • dnSpyEx: Much like ILSpy, nevertheless it permits you to debug and even edit assemblies
  • IL2CppDumper: Extracts the supply code from video games that had been constructed with IL2CPP
  • AssetRipper: An alternative choice to AssetStudio to extract property

Thanks for studying this tutorial to the top! When you’ve got any questions or feedback, be at liberty to affix the dialogue beneath.

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