Help needed modifying Pokemon Crystal VC ROM/Full screen Frame

[Staticasaurus]

Hi there. I am trying to modify the Virtual Console full screen frame of Pokémon Crystal (the one you get when you press start or select). I'm having some issues.

I have CFW homebrew on my 3DS with Luma, and access to a CIA installer and Godmode9.

What I did:
I used godmode9 to dump the Pokémon Crystal VC ROM. Then I used Ultimate GBC VC Injector to inject the custom frame and create a CIA from the ROM.

Now I have a CIA file, but I don't want to just install that file. Firstly, I have a save file I want to retain. And more importantly, the official Pokémon Crystal VC has patches that come installed with the app that I want to still have access to (wireless trading, Celebi event, etc).

So, I have some questions that I was hoping that someone could help me with:
1. When I used Godmode9 to dump the rom, there were 2 .app files, and I dumped the larger of the two.  What was the other .app file?  Is it the patches? There was also a .tmp file, but I think that's standard. 

2. Are the patches applied to the ROM itself? If so, then I could just back up my save with JKSM, install the CIA I created, and then restore my save file with JKSM.

3.  If the patches *arent* applied to the ROM, can I somehow just reinject the modified ROM/CIA back into the original app? Or apply the patches myself?

4.  Probably the easiest thing to do (and avoid everything above) would be to modify just the file with the Full Screen Virtual Console Frame.  Is it possible to do that?  And if so, how?

Can anyone help me?  I'm self taught as far as hacking goes, and I'm really unfamiliar with how VC titles are implemented with patches and everything.  More than getting help doing the thing, I'm hoping to learn more about what I'm fooling around with.  Its been fun, and I'd like to better understand the tech.

Edited November 1, 2021 by Staticasaurus

[theSLAYER]

It's been a while since I missed with VC edits. I *think* you need to decompile the .app file to get separate files. GodMode9 should be able to do that.

Once done, you'll find the GB/GBC ROM for the Pokemon game + all the patch files.
There will be more than one patch file, with various patch files for different Pokemon games and languages (even tho you're technically only working on one single game.) The patch files should have the GB/GBC game IDs in it.

I don't know anything about modifying the VC frame itself, never tried it.

[Staticasaurus]

I think youre saying dump the romFS, right?  

I dumped the rom instead, and only got the one file.  

Any idea why there would be 2 .app files?

[theSLAYER]

26 minutes ago, Staticasaurus said:

I think youre saying dump the romFS, right?  

I dumped the rom instead, and only got the one file.  

Any idea why there would be 2 .app files?

To be frank, it's been a while since I've dealt with them and had to think about them.
Try to see which could be mounted and would give you the files.

The game name should correspond to the patch. I've managed to find one of the game names from my older extracts, and it is something like

Spoiler

Dmgapae0.e69

As for why there are 2.app files, no clue. I think there being more than 1 is normal even for 3DS titles tho.

Edit:
Yup, perform the standard steps to dump romfs, including mounting 00000001.app image to drive, then viewing it.

The ROM is in a folder called rom, and all the patches are outside.

[Staticasaurus]

OK that makes sense.  So, the file I am after is the one that has the VC frame.  Do you know which file that might be?  The frame I am talking about is the one that pops up when you launch the app while holding start or select. 

Edited November 1, 2021 by Staticasaurus

[theSLAYER]

51 minutes ago, Staticasaurus said:

OK that makes sense.  So, the file I am after is the one that has the VC frame.  Do you know which file that might be?  The frame I am talking about is the one that pops up when you launch the app while holding start or select. 

As I said earlier, I've not edited that frame before, no idea where it is. That appears to be beyond the scope of editing stuff niche to Pokemon, but rather all VC edits in general, so you may have better luck searching the net for general VC edits.

For now, I'm trying to scour the net for it too.

edit: Linking to our discussion on Discord for posterity: https://discord.com/channels/343093766477053953/367479180398428170/904804660328673370

[Staticasaurus]

Updating this thread with a solid path forward for those that come looking after me. 

The second .app file was the manual.  The patches are not applied to the ROM, rather, they are located in the RomFS, and seem to run with the ROM.  If dumping the ROM grabs the entire RomFS (I think it should), then the patches went with it.

So rather than tool around with reinstalling my CIA and then backing my up save from the original and injecting it into mine, the general process I'm going to try is:

1. Use godmode9 to dump the Rom of the official Pokemon Crystal VC. 
2. Use that ROM in conjunction with NSUI and my custom faceplate PNG to create a new installable CIA.  
3. Install the CIA, then use godmode9 to dump the Romfs, and get the (hopefully) updated face_cgb(dot)ttp file.  The hope here is that NSUI correctly coded my PNG into the tpp file, which will be found at the bottom of the root directory for the RomFS.
4. Delete the app I created and installed.
5. Use layeredFS to replace the original face_cgb(dot)tpp with the file I got out of the CIA I created. 

If all goes well, it should work.  I'll update back when I figure out if it worked or not. 

 

[Staticasaurus]

It worked!  I will be posting a tutorial on how to do this, from start to finish.  Stay tuned!