Commonwealth-Online-Public/docs/FFDEC_MainMenu_Multiplayer_Guide.md

FFDec guide — add Multiplayer button to MainMenu.swf

Deprecated: Use C++ runtime injection instead. See MainMenu_Injection.md. Do not deploy a patched MainMenu.swf for Commonwealth Online.

Step-by-step instructions for adding the Multiplayer main-menu item using JPEXS FFDec, without breaking Settings → Gameplay / Display / Audio.

This guide is kept for historical reference only.

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Before you start

Restore vanilla SWF

Always patch from the vanilla file, not an old broken copy:

.\tools\restore-vanilla-mainmenu.ps1

Or manually copy Interface/MainMenu.swf.vanilla.bak → Interface/MainMenu.swf.

Vanilla size is 61,959 bytes. If your file is 64 KB+, it is probably a bad re-import — restore and start again.

Requirements

• FFDec installed
• Game launched via F4SE with CommonwealthOnline.dll in Data/F4SE/Plugins/
• Loose Interface overrides enabled in %USERPROFILE%/Documents/My Games/Fallout4/Fallout4Custom.ini:

[Archive]
bInvalidateOlderFiles=1

Critical rule

Do	Don't
Edit individual methods (double-click method in traits list)	Paste the full MainMenu.as export into the class editor
Save after each small edit	Use Import script on the whole MainMenu class
Keep SWF ~62–63 KB	Re-export the entire decompiled script

Full re-import recompiles RequestOptions and breaks settings sub-menus. Controls will still work; Gameplay / Display / Audio will crash.

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FFDec navigation

1. Open Interface/MainMenu.swf in FFDec.
2. Left tree: scripts → MainMenu.
3. You should see a traits / members list (constants, functions).
4. Double-click a method name (e.g. InitList) to open only that method in the editor.
5. After each edit: apply/save the method, then File → Save the SWF.

Do not use Edit ActionScript on the entire MainMenu class if FFDec offers a single giant class view — use per-method editing instead.

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Summary of changes

#	Where in FFDec	What
1	Class constants	Add MULTIPLAYER_INDEX
2	Method InitList	Push Multiplayer row after Load
3	Method onMainListItemPress	Add case for Multiplayer
4	New method CloseMultiplayerBrowser	Helper (recommended)
5	Method set currentState	Call close helper when leaving main panel
6	Method onMainListItemPress	Close browser when another item is selected

Changes 4–6 are recommended so the HTML browser closes immediately when opening Settings, etc. The plugin also hides the browser when currentState leaves MAIN_STATE, but the SWF hooks make it feel instant.

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Change 1 — Add index constant

FFDec: MainMenu → constants section (near other *_INDEX constants)

Find this block (search for INSTALLED_CONTENT_INDEX):

      private const INSTALLED_CONTENT_INDEX:Number = 14;
      
      private const MAIN_PANEL_BACKGROUND:uint = 0;

Insert between those lines:

      private const MULTIPLAYER_INDEX:Number = 15;

Index 15 is unused in vanilla (highest defined index is 14).

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Change 2 — Add menu row in InitList

FFDec: MainMenu → method InitList

Find this block (search for "$LOAD" push — it appears after the $NEW block on title screen):

         this.MainPanel_mc.List_mc.entryList.push({
            "text":"$LOAD",
            "disabled":!this.HasRecentSave || !param6,
            "index":this.LOAD_INDEX
         });
         if(param8 == true)

Replace with (add Multiplayer block between Load and if(param8 == true)):

         this.MainPanel_mc.List_mc.entryList.push({
            "text":"$LOAD",
            "disabled":!this.HasRecentSave || !param6,
            "index":this.LOAD_INDEX
         });
         if(!this.PauseMode)
         {
            this.MainPanel_mc.List_mc.entryList.push({
               "text":"Multiplayer",
               "index":this.MULTIPLAYER_INDEX
            });
         }
         if(param8 == true)

Notes:

• "Multiplayer" is a literal label (no $ prefix). Strings with $ are looked up in Interface/Translate_en.txt.
• !this.PauseMode limits the row to the title screen, not the in-game pause menu.
• Row appears between Load and Add-ons (or PS5 transfer if enabled).

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Change 3 — Handle click in onMainListItemPress

FFDec: MainMenu → method onMainListItemPress

Find this block (search for case this.HELP_INDEX:):

                  break;
               case this.HELP_INDEX:
                  this.StartState(this.HELP_STATE);
                  this.BGSCodeObj.PlayOKSound();
                  break;

Insert immediately before case this.HELP_INDEX::

                  break;
               case this.MULTIPLAYER_INDEX:
                  this.BGSCodeObj.PlayOKSound();
                  if(root.f4se != null && root.f4se.plugins != null && root.f4se.plugins.commonwealthOnline != null)
                  {
                     root.f4se.plugins.commonwealthOnline.openManager();
                  }
                  break;
               case this.HELP_INDEX:
                  this.StartState(this.HELP_STATE);
                  this.BGSCodeObj.PlayOKSound();
                  break;

This calls the C++ API registered by CommonwealthOnline.dll (openManager → PrismaUI server browser). F9 still toggles the same browser.

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Change 4 — Add CloseMultiplayerBrowser method

FFDec: MainMenu → add new method (right-click class → Add script / Add method, or paste near other private helpers like onMainListItemPress)

Add this entire method:

      private function CloseMultiplayerBrowser() : *
      {
         if(root.f4se != null && root.f4se.plugins != null && root.f4se.plugins.commonwealthOnline != null)
         {
            root.f4se.plugins.commonwealthOnline.closeManager();
         }
      }

---

Change 5 — Close browser in set currentState

FFDec: MainMenu → method set currentState (may appear as currentState setter)

Find:

      public function set currentState(param1:String) : *
      {
         this.strCurrentState = param1;
         this.UpdateButtons(param1);
         this.UpdateStateFocus(param1);
      }

Change to:

      public function set currentState(param1:String) : *
      {
         this.strCurrentState = param1;
         if(param1 != this.MAIN_STATE)
         {
            this.CloseMultiplayerBrowser();
         }
         this.UpdateButtons(param1);
         this.UpdateStateFocus(param1);
      }

---

Change 6 — Close browser when another main-menu item is selected

FFDec: MainMenu → method onMainListItemPress (same method as Change 3)

Find the start of the else branch, after the while loop that returns to main state:

            while(this.strCurrentState != this.MAIN_STATE)
            {
               this.onCancelPress(true,false);
            }
            if(this.MainPanel_mc.List_mc.selectedEntry.index == this.CONTINUE_INDEX && this.PauseMode)

Insert between the while loop and the CONTINUE_INDEX check:

            while(this.strCurrentState != this.MAIN_STATE)
            {
               this.onCancelPress(true,false);
            }
            if(this.MainPanel_mc.List_mc.selectedEntry.index != this.MULTIPLAYER_INDEX)
            {
               this.CloseMultiplayerBrowser();
            }
            if(this.MainPanel_mc.List_mc.selectedEntry.index == this.CONTINUE_INDEX && this.PauseMode)

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Save and deploy

1. File → Save in FFDec (overwrite Interface/MainMenu.swf).

2. Check file size: should be roughly 62,000–63,500 bytes. If 64,000+, restore vanilla and redo using method-only edits.

3. Copy to game:

   Fallout 4/Data/Interface/MainMenu.swf
   

4. Launch via F4SE.

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Test checklist

Step	Expected
Main menu (title screen)	Multiplayer appears after Load
Pause menu → Settings	No Multiplayer row
Click Multiplayer	Server browser opens
Settings → Gameplay	No crash
Settings → Display	No crash
Settings → Audio	No crash
Settings → Controls	Still works
Open Multiplayer, then Settings	Browser closes
F9	Still toggles browser

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Troubleshooting

Settings sub-menus crash again

You likely re-imported the full class. Run .\tools\restore-vanilla-mainmenu.ps1 and redo changes 1–6 using per-method editing only.

Multiplayer row missing

• Confirm bInvalidateOlderFiles=1 in Fallout4Custom.ini.
• Confirm loose Data/Interface/MainMenu.swf exists and is not overridden by another mod (check MO2 load order).
• Confirm you added the InitList block with if(!this.PauseMode).

Multiplayer row visible but click does nothing

• Launch via F4SE, not vanilla exe.
• Confirm CommonwealthOnline.dll is loading (check Documents/My Games/Fallout4/F4SE/CommonwealthOnline.log).
• Confirm Change 3 (case this.MULTIPLAYER_INDEX) is present.

Button shows $MULTIPLAYER or wrong text

Use literal "Multiplayer" (no $), or add a translation key to Interface/Translate_en.txt.

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Reference files

File	Purpose
MainMenu.swf.vanilla.bak	Untouched vanilla backup
scripts/MainMenu.as	Full decompiled reference — do not import wholesale
PATCH_MainMenu_Multiplayer.md	Short overview
../../tools/restore-vanilla-mainmenu.ps1	Restore vanilla SWF from game BA2

Plugin API (already implemented in C++):

• root.f4se.plugins.commonwealthOnline.openManager()
• root.f4se.plugins.commonwealthOnline.closeManager()