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BCML: BOTW Cross-Platform Mod Loader - A Modding Tool for The Legend of Zelda: Breath of the Wild (WiiU).

A mod merger and manager for BOTW

1. A Mod Loader?

Why a mod loader for BOTW? Installing a mod is usually easy enough once you have a homebrewed console or a emulator. Is there a need for a special tool?

Yes. As soon as you start trying to install multiple mods, you will find complications. The BOTW game ROM is fundamentally structured for performance and storage use on a family console, without any support for modification. As such, files like the resource size table or TitleBG.pack will almost inevtiably begin to clash once you have more than a mod or two. Symptoms can include mods simply taking no effect, odd bugs, actors that don't load, hanging on the load screen, or complete crashing. BCML exists to resolve this problem. It identifies, isolates, and merges the changes made by each mod into a single modpack that just works.

2. Prerequisites

  • Windows 10 (7-8 might work but are not supported) or basically any modern Linux distribution
  • A legal, unpacked game dump of The Legend of Zelda: Breath of the Wild for Wii U (version 1.5.0)
  • The latest x64 Visual C++ redistributable

3. Setup

There are two primary options for installing BCML. 

The best way is to install BCML from PyPI. For help with this, consult the video tutorial at the top of this page.

  1. Make sure you already have the latest x64 Visual C++ installed.
  2. Install Python 3.7 - 3.9 (64 bit), making sure to checl Add Python to PATH.
  3. Install BCML using pip in a Command Prompt: pip install bcml
  4. Run BCML using the command bcml or by making a shortcut to bcml.exe, which is located in Python's Scripts folder.
You can also install from source.

On first use, you will have to point BCML to the directories containing your unpacked base game and DLC files. The first run wizard will try to guide you.

4. Usage and Troubleshooting

For information on how to use BCML, watch the intro video above, see the Help dialog in-app, or read the documentation on the repo. For issues and troubleshooting, please check the in-app help and the official Troubleshooting page before commenting.

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  • Lemon Fry avatar
    Lemon Fry Joined 1y ago
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    16hr
    How long does it usually take to export mods for use on the Switch version? I've been sitting on this loading screen for like an hour and I can't tell if it's doing anything. 
    Bananite
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  • TwinbeeMkII avatar
    TwinbeeMkII Joined 4y ago
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    22hr
    Wasn't sure where else to put this. I ran into an error, and after hours of scouring troubleshooting and comment sections, the 2-3 times this same issues arose, I saw no response to it, so please help me if you can. Mods were working fine for awhile, but I'm not sure if I did something wrong, but now this error pops up when trying to install or change any mods, and the game won't load up:

    Traceback (most recent call last):
    File "C:\Users\jek1\AppData\Local\Programs\Python\Python38\lib\site-packages\bcml\_api.py", line 564, in remerge
    install.refresh_merges()
    File "C:\Users\jek1\AppData\Local\Programs\Python\Python38\lib\site-packages\bcml\install.py", line 602, in refresh_merges
    merger.perform_merge()
    File "C:\Users\jek1\AppData\Local\Programs\Python\Python38\lib\site-packages\bcml\util.py", line 464, in timed_function
    res = func(*args, **kwargs)
    File "C:\Users\jek1\AppData\Local\Programs\Python\Python38\lib\site-packages\bcml\mergers\mubin.py", line 723, in perform_merge
    rstb_vals = rsext.mergers.maps.merge_maps(oead.byml.to_binary(map_diffs, True))
    RuntimeError: failed to fill whole buffer

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
    File "C:\Users\jek1\AppData\Local\Programs\Python\Python38\lib\site-packages\bcml\_api.py", line 33, in status_run
    data = func(*args, **kwargs)
    File "C:\Users\jek1\AppData\Local\Programs\Python\Python38\lib\site-packages\bcml\install.py", line 264, in do_and_refresh
    res = func(*args, **kwargs)
    File "C:\Users\jek1\AppData\Local\Programs\Python\Python38\lib\site-packages\bcml\_api.py", line 572, in remerge
    raise Exception(
    Exception: There was an error merging your mods. failed to fill whole buffer
    Note that this could leave your game in an unplayable state.
    Bananite
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  • Hi there. I followed the guide on how to install BCML and it's coming up with this error. I'm not too sure what to do to fix it.
    Bananite
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  • NahoFiend avatar
    NahoFiend Joined 12mo ago
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    Why does the install have to be so complicated? Why can't it just be an exe file like it used to be. I follow all of the steps and I can't get it to install so I can't use the most recent mods that require the latest update. I'm still using a version from like 2 years ago. I can't get it to just update, but as I said, I can't install the new one either.
    Bananite
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  • When I try to export mods it does a infinite loading and it never exports. And I tried to use the one in explore but when I launch the game its either vanilla or its infinitely loading.

    Bananite
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  • Where can I download the latest build of BCML?
    Bananite
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  • MelNara avatar
    MelNara Joined 2y ago
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    Hi. I keep getting this error when installing some mods or changing mod load order. 

    Traceback (most recent call last):

      File "c:\python38\lib\site-packages\bcml\_api.py", line 33, in status_run

        data = func(*args, **kwargs)

      File "c:\python38\lib\site-packages\bcml\_api.py", line 471, in apply_queue

        install.refresh_merges()

      File "c:\python38\lib\site-packages\bcml\install.py", line 602, in refresh_merges

        merger.perform_merge()

      File "c:\python38\lib\site-packages\bcml\util.py", line 464, in timed_function

        res = func(*args, **kwargs)

      File "c:\python38\lib\site-packages\bcml\mergers\mubin.py", line 723, in perform_merge

        rstb_vals = rsext.mergers.maps.merge_maps(oead.byml.to_binary(map_diffs, True))

    RuntimeError: failed to fill whole buffer

    Not sure what the problem is.

    Bananite
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  • Amppelix avatar
    Amppelix Joined 4y ago
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    I had everything working fine, but after recently changing my Cemu folder, it appears BCML is incapable of actually installing the mods to that new location. they always went to the old folder despite me changing it in the settings, and after i deleted the old cemu folder they just go nowhere at all. of course it still works by just manually copying, but it is a bit annoying. This even persists after i delete the whole bcml data folder and start fresh, so you really must've saved that connection somewhere real deep!
    Bananite
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  • Kitsune009 avatar
    Kitsune009 Joined 1y ago
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    23d
    i keep getting an error, asking me to install pyproject.toml. i simply followed the step by step instructions but that error happens.
    Bananite
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  • ModernJayTHYT avatar
    ModernJayTHYT Joined 2y ago
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    27d
    So.. i tried to reinstall everything. But nothing works. BCML wont boot up at all. And unfortunately there is no way i can make it work. Not sure if there is a workaround for it but it would be really appreciated to play BOTW mods again.
    Bananite
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