Borderless Full Screen

Game must be set to windowed mode for this to work properly.

-1.0.1: The mod will do this for you.

+2.0.0: Mod doesn't do this anymore to maintain compatibility with other games that can also utilize BepInEx, you can use the command below to ensure the game starts in windowed mode.

Launch Unity games in windowed mode with this command:

-screen-fullscreen 0

2.0.0+

No longer use Autohotkey.Interop dependency, instead just do what the ahk script did:

public class BorderlessFullScreenPlugin : BaseUnityPlugin
{
    [DllImport("user32.dll")]
    private static extern IntPtr FindWindow(string className, string windowName);

    [DllImport("user32.dll")]
    private static extern int GetWindowLong(IntPtr hWnd, int index);

    [DllImport("user32.dll")]
    private static extern int SetWindowLong(IntPtr hWnd, int index, int value);

    [DllImport("user32.dll")]
    private static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int x, int y, int width, int height, uint flags);

    private const int GWL_STYLE = -16;
    private const uint SWP_FRAMECHANGED = 0x0020;
    private const uint SWP_SHOWWINDOW = 0x0040;

    private void Start()
    {
        IntPtr hWnd = FindWindow("UnityWndClass", null);
        if (hWnd != IntPtr.Zero)
        {
            int style = GetWindowLong(hWnd, GWL_STYLE);
            style &= ~0xC40000; // Remove WS_BORDER and WS_CAPTION
            SetWindowLong(hWnd, GWL_STYLE, style);

            SetWindowPos(hWnd, IntPtr.Zero, 0, 0, Screen.width, Screen.height, SWP_FRAMECHANGED | SWP_SHOWWINDOW);
        }
        else
        {
            Debug.LogError("Unity window not found.");
        }

        Debug.Log($"Plugin {"BorderlessFullscreen"} is loaded!");
    }
}

Old Description for version 1.0.1

Uses AutoHotkey.Interop to execute the following AutoHotkey script into the game through BepInEx.

procName := "UnityWndClass"
WinGet Style, Style, % "ahk_class " procName
If (Style & 0xC40000)
{
WinSet, Style, -0xC40000, % "ahk_class " procName
WinMove, % "ahk_class " procName, , 0, 0, A_ScreenWidth + 1, A_ScreenHeight + 1
}
Return