From 5812065b56558fa52c955d9459522d8aaca249f7 Mon Sep 17 00:00:00 2001
From: OctoWoW <noreply@octowow.st>
Date: Thu, 9 Jul 2026 21:58:15 -0700
Subject: [PATCH] Fix monitor resolution issue with correct monitor detection

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 package.json                 |  2 +-
 src/main/modules/displays.ts | 76 ++++++++++++++++++++++++++++++++++++
 src/main/modules/mods.ts     |  7 +++-
 3 files changed, 82 insertions(+), 3 deletions(-)
 create mode 100644 src/main/modules/displays.ts

diff --git a/package.json b/package.json
index 7e393f3..d264763 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
 	"name": "octo-launcher",
-	"version": "1.2.0",
+	"version": "1.2.1",
 	"description": "An Electron application for launching and updating the OctoWoW client",
 	"author": "OctoWoW",
 	"copyright": "Copyright © 2026 OctoWoW",
diff --git a/src/main/modules/displays.ts b/src/main/modules/displays.ts
new file mode 100644
index 0000000..a1ee0eb
--- /dev/null
+++ b/src/main/modules/displays.ts
@@ -0,0 +1,76 @@
+import os from 'node:os';
+import { spawn } from 'node:child_process';
+
+import Logger from 'electron-log/main';
+
+const SCRIPT = [
+	'$ErrorActionPreference = "Stop"',
+	"Add-Type -TypeDefinition @'",
+	'using System;',
+	'using System.Runtime.InteropServices;',
+	'public static class VmmfDisplays {',
+	'  [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi)]',
+	'  public struct DISPLAY_DEVICE {',
+	'    public int cb;',
+	'    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=32)] public string DeviceName;',
+	'    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=128)] public string DeviceString;',
+	'    public int StateFlags;',
+	'    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=128)] public string DeviceID;',
+	'    [MarshalAs(UnmanagedType.ByValTStr, SizeConst=128)] public string DeviceKey;',
+	'  }',
+	'  [DllImport("user32.dll", EntryPoint="EnumDisplayDevicesA", CharSet=CharSet.Ansi)]',
+	'  public static extern bool EnumDisplayDevices(string lpDevice, uint iDevNum, ref DISPLAY_DEVICE lpDisplayDevice, uint dwFlags);',
+	'}',
+	"'@",
+	'$dd = New-Object VmmfDisplays+DISPLAY_DEVICE',
+	'$dd.cb = [System.Runtime.InteropServices.Marshal]::SizeOf($dd)',
+	'for ($i = 0; [VmmfDisplays]::EnumDisplayDevices([NullString]::Value, $i, [ref]$dd, 0); $i++) {',
+	'  if ($dd.StateFlags -band 4) { Write-Output $i; exit 0 }',
+	'}',
+	'exit 1'
+].join('\n');
+
+export const detectPrimaryDisplayIndex = (): Promise<number> => {
+	if (os.platform() !== 'win32') return Promise.resolve(0);
+
+	const encoded = Buffer.from(SCRIPT, 'utf16le').toString('base64');
+
+	return new Promise(resolve => {
+		let settled = false;
+		const finish = (index: number) => {
+			if (settled) return;
+			settled = true;
+			clearTimeout(timer);
+			resolve(index);
+		};
+
+		const child = spawn(
+			'powershell.exe',
+			['-NoProfile', '-NonInteractive', '-EncodedCommand', encoded],
+			{ windowsHide: true }
+		);
+
+		const timer = setTimeout(() => {
+			child.kill();
+			Logger.warn('Primary display detection timed out');
+			finish(0);
+		}, 8000);
+
+		let stdout = '';
+		child.stdout.on('data', d => (stdout += String(d)));
+		child.on('error', e => {
+			Logger.warn('Primary display detection failed to launch PowerShell', e);
+			finish(0);
+		});
+		child.on('exit', code => {
+			const index = Number(stdout.trim());
+			if (code === 0 && Number.isInteger(index) && index >= 0) {
+				Logger.info(`Detected primary display at device index ${index}`);
+				finish(index);
+			} else {
+				Logger.warn('Primary display detection failed, defaulting to 0');
+				finish(0);
+			}
+		});
+	});
+};
diff --git a/src/main/modules/mods.ts b/src/main/modules/mods.ts
index cdaf799..d8eaf59 100644
--- a/src/main/modules/mods.ts
+++ b/src/main/modules/mods.ts
@@ -13,6 +13,7 @@ import Preferences from './preferences';
 import Observable from './observable';
 import Updater from './updater';
 import { addDll, removeDll } from './dllsTxt';
+import { detectPrimaryDisplayIndex } from './displays';
 
 const MOD_DOWNLOAD_TIMEOUT_MS = 60_000;
 
@@ -113,8 +114,10 @@ class ModsClass extends Observable<ModsStatus> {
 		if (clientDir) {
 			const vmmfDll = path.join(clientDir, 'VanillaMultiMonitorFix.dll');
 			const vmmfCfg = path.join(clientDir, 'VMMFix_preferred_monitor.txt');
-			if ((await fs.pathExists(vmmfDll)) && !(await fs.pathExists(vmmfCfg)))
-				await fs.writeFile(vmmfCfg, '0\n', 'utf8').catch(() => {});
+			if ((await fs.pathExists(vmmfDll)) && !(await fs.pathExists(vmmfCfg))) {
+				const index = await detectPrimaryDisplayIndex();
+				await fs.writeFile(vmmfCfg, `${index}\n`, 'utf8').catch(() => {});
+			}
 		}
 
 		for (const m of MODS) {