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Cities-Skylines-2-MacOS-Patcher

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Automated patcher to make Cities Skylines 2 work with Crossover on Mac

// repository documentation

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# Cities: Skylines II - macOS Patch

**Tested with game version 1.5.5f1 on CrossOver 26.0** — the patcher uses
pattern matching and should work with other versions, but if a patch fails
after an update, check for an updated version of this patcher.

Fixes that allow Cities: Skylines II to run on macOS via CrossOver or Whisky (Wine).
The game has several Wine compatibility issues caused by Win32 API calls that
behave differently under Wine on macOS. This patcher applies binary fixes to
three game DLLs to work around them.

## Installation

Place the `mac_patch` folder inside the game's root directory so the structure
looks like this:

```
Cities Skylines II/
  Cities2_Data/
  Cities2.exe
  mac_patch/          <-- here
    patch.sh
    patch_cohtml.py
    patch_colossal_io.py
    patch_asset_database.py
```

### Finding the game directory

**CrossOver:**
1. Open CrossOver, right-click your bottle, select "Open C: Drive"
2. Navigate to `Program Files (x86)/Steam/steamapps/common/Cities Skylines II/`

Or in terminal:
```
~/Library/Application Support/CrossOver/Bottles/<BOTTLE>/drive_c/Program Files (x86)/Steam/steamapps/common/Cities Skylines II/
```

**Whisky:**
1. Open Whisky, click your bottle, click "Open Bottle Directory"
2. Navigate to `drive_c/Program Files (x86)/Steam/steamapps/common/Cities Skylines II/`

Or in terminal:
```
~/Library/Containers/com.isaacmarovitz.Whisky/Bottles/<BOTTLE>/drive_c/Program Files (x86)/Steam/steamapps/common/Cities Skylines II/
```

Replace `<BOTTLE>` with the name of your Wine bottle.

## Usage

Open Terminal and run:

```bash
cd "<path to Cities Skylines II>"
bash mac_patch/patch.sh
```

The patcher will:
- Back up each original DLL before modifying it (`.bak` files)
- Apply all three patches
- Skip already-patched files safely (can be re-run without harm)
- Refresh backups automatically when a game update is detected

**Re-run after every game update** — Steam overwrites the patched DLLs
with fresh copies when the game updates.

## Prerequisites

- macOS with CrossOver or Whisky
- Python 3 (ships with macOS)

## What It Fixes

### 1. UI rendering crash (cohtml_Unity3DPlugin.dll)

**Symptom:** Game crashes before reaching the main menu.

**Cause:** The Cohtml UI rendering plugin has a conditional branch in its
IAllocator initialization that takes the wrong code path under Wine/GPTK,
causing an access violation.

**Patch:** Flips a `je` (jump if equal) instruction to `jne` (jump if not
equal) so the correct code path is taken. Uses the same signature pattern as
[cities2-gptk-fix](https://github.com/manolz1/cities2-gptk-fix) to find
the instruction automatically across game versions.

### 2. Startup crash (Colossal.IO.dll)

**Symptom:** Game crashes immediately on startup with an unhandled exception.

**Cause:** After enumerating files in a directory, the game calls
`Marshal.GetLastWin32Error()` and throws an exception if the error code
is not `ERROR_NO_MORE_FILES` (18). Under Wine on macOS, `GetLastWin32Error()`
returns random/garbage values instead of the correct error code.

**Patch:** Replaces the error check with an unconditional branch to the
normal exit path, bypassing the `GetLastWin32Error` + `throw` block entirely.
Applied to both `EnumerateFileSystemIterator` and
`EnumerateFileSystemIteratorRecursive` in `LongDirectory`.

### 3. Asset loading errors (Colossal.IO.AssetDatabase.dll)

**Symptom:** `[ERROR] Error occured populating data source FileSystemDataSource`
with `FileNotFoundException` for `.priority` files.

**Cause:** The asset database checks `File.Exists(".priority")` before reading
it. Under Wine, `File.Exists()` returns incorrect results — it reports the file
exists when it doesn't. The subsequent `File.ReadAllLines()` then throws.

The `.priority` file is an optional text file that lists assets to load first.
It is not required for the game to function.

**Patch:** Replaces `call File::Exists` with `pop + ldc.i4.0` so the result
is always `false`, causing the branch to always skip the `.priority` read block.

## Installing Mods

The in-game Paradox Mods installer **does not work** under Wine. It shows
"Error reading or writing to disk" because the Paradox SDK (`PDX.SDK.dll`) uses
native Win32 API calls for file operations that are broken under Wine on macOS.

Use **Skyve** instead — a third-party mod manager that uses standard .NET file
I/O, which works correctly under Wine.

### Installing Skyve

1. Go to https://mods.paradoxplaza.com/mods/75804/Windows
2. Click the download link to get the zip file
3. Extract the zip
4. Run the Skyve setup executable inside your Wine bottle

Once installed, use Skyve to browse, install, and manage all your mods.

## Restoring Original DLLs

Backups are stored next to the patched DLLs with a `.bak` extension:

```
Cities2_Data/Plugins/x86_64/cohtml_unity3dplugin.dll.bak
Cities2_Data/Managed/Colossal.IO.dll.bak
Cities2_Data/Managed/Colossal.IO.AssetDatabase.dll.bak
```

To restore all originals:

```bash
cd "<path to Cities Skylines II>"
cp Cities2_Data/Plugins/x86_64/cohtml_unity3dplugin.dll.bak Cities2_Data/Plugins/x86_64/cohtml_unity3dplugin.dll
cp Cities2_Data/Managed/Colossal.IO.dll.bak Cities2_Data/Managed/Colossal.IO.dll
cp Cities2_Data/Managed/Colossal.IO.AssetDatabase.dll.bak Cities2_Data/Managed/Colossal.IO.AssetDatabase.dll
```

Cities-Skylines-2-MacOS-Patcher

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