DisplayUtils.cs

using System.Runtime.InteropServices;


public class DisplayUtils
{
    [StructLayout(LayoutKind.Explicit, CharSet = CharSet.Ansi)]
    struct DEVMODE
    {
        public const int CCHDEVICENAME = 32;
        public const int CCHFORMNAME = 32;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCHDEVICENAME)]
        [System.Runtime.InteropServices.FieldOffset(0)]
        public string dmDeviceName;
        [System.Runtime.InteropServices.FieldOffset(32)]
        public Int16 dmSpecVersion;
        [System.Runtime.InteropServices.FieldOffset(34)]
        public Int16 dmDriverVersion;
        [System.Runtime.InteropServices.FieldOffset(36)]
        public Int16 dmSize;
        [System.Runtime.InteropServices.FieldOffset(38)]
        public Int16 dmDriverExtra;
        [System.Runtime.InteropServices.FieldOffset(40)]
        public DM dmFields;

        [System.Runtime.InteropServices.FieldOffset(44)]
        Int16 dmOrientation;
        [System.Runtime.InteropServices.FieldOffset(46)]
        Int16 dmPaperSize;
        [System.Runtime.InteropServices.FieldOffset(48)]
        Int16 dmPaperLength;
        [System.Runtime.InteropServices.FieldOffset(50)]
        Int16 dmPaperWidth;
        [System.Runtime.InteropServices.FieldOffset(52)]
        Int16 dmScale;
        [System.Runtime.InteropServices.FieldOffset(54)]
        Int16 dmCopies;
        [System.Runtime.InteropServices.FieldOffset(56)]
        Int16 dmDefaultSource;
        [System.Runtime.InteropServices.FieldOffset(58)]
        Int16 dmPrintQuality;

        [System.Runtime.InteropServices.FieldOffset(44)]
        public POINTL dmPosition;
        [System.Runtime.InteropServices.FieldOffset(52)]
        public Int32 dmDisplayOrientation;
        [System.Runtime.InteropServices.FieldOffset(56)]
        public Int32 dmDisplayFixedOutput;

        [System.Runtime.InteropServices.FieldOffset(60)]
        public short dmColor;
        [System.Runtime.InteropServices.FieldOffset(62)]
        public short dmDuplex;
        [System.Runtime.InteropServices.FieldOffset(64)]
        public short dmYResolution;
        [System.Runtime.InteropServices.FieldOffset(66)]
        public short dmTTOption;
        [System.Runtime.InteropServices.FieldOffset(68)]
        public short dmCollate;
        [System.Runtime.InteropServices.FieldOffset(72)]
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCHFORMNAME)]
        public string dmFormName;
        [System.Runtime.InteropServices.FieldOffset(102)]
        public Int16 dmLogPixels;
        [System.Runtime.InteropServices.FieldOffset(104)]
        public Int32 dmBitsPerPel;
        [System.Runtime.InteropServices.FieldOffset(108)]
        public Int32 dmPelsWidth;
        [System.Runtime.InteropServices.FieldOffset(112)]
        public Int32 dmPelsHeight;
        [System.Runtime.InteropServices.FieldOffset(116)]
        public Int32 dmDisplayFlags;
        [System.Runtime.InteropServices.FieldOffset(116)]
        public Int32 dmNup;
        [System.Runtime.InteropServices.FieldOffset(120)]
        public Int32 dmDisplayFrequency;
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    struct DISPLAY_DEVICE
    {
        [MarshalAs(UnmanagedType.U4)]
        public int cb;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
        public string DeviceName;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
        public string DeviceString;
        [MarshalAs(UnmanagedType.U4)]
        public DisplayDeviceStateFlags StateFlags;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
        public string DeviceID;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
        public string DeviceKey;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct POINTL
    {
        long x;
        long y;
    }

    enum DISP_CHANGE : int
    {
        Successful = 0,
        Restart = 1,
        Failed = -1,
        BadMode = -2,
        NotUpdated = -3,
        BadFlags = -4,
        BadParam = -5,
        BadDualView = -6
    }

    [Flags()]
    enum DisplayDeviceStateFlags : int
    {
        /// <summary>The device is part of the desktop.</summary>
        AttachedToDesktop = 0x1,
        MultiDriver = 0x2,
        /// <summary>The device is part of the desktop.</summary>
        PrimaryDevice = 0x4,
        /// <summary>Represents a pseudo device used to mirror application drawing for remoting or other purposes.</summary>
        MirroringDriver = 0x8,
        /// <summary>The device is VGA compatible.</summary>
        VGACompatible = 0x10,
        /// <summary>The device is removable; it cannot be the primary display.</summary>
        Removable = 0x20,
        /// <summary>The device has more display modes than its output devices support.</summary>
        ModesPruned = 0x8000000,
        Remote = 0x4000000,
        Disconnect = 0x2000000
    }

    [Flags()]
    enum DisplaySettingsFlags : int
    {
        CDS_NONE = 0,
        CDS_UPDATEREGISTRY = 0x00000001,
        CDS_TEST = 0x00000002,
        CDS_FULLSCREEN = 0x00000004,
        CDS_GLOBAL = 0x00000008,
        CDS_SET_PRIMARY = 0x00000010,
        CDS_VIDEOPARAMETERS = 0x00000020,
        CDS_ENABLE_UNSAFE_MODES = 0x00000100,
        CDS_DISABLE_UNSAFE_MODES = 0x00000200,
        CDS_RESET = 0x40000000,
        CDS_RESET_EX = 0x20000000,
        CDS_NORESET = 0x10000000
    }

    [Flags()]
    enum DM : int
    {
        Orientation = 0x00000001,
        PaperSize = 0x00000002,
        PaperLength = 0x00000004,
        PaperWidth = 0x00000008,
        Scale = 0x00000010,
        Position = 0x00000020,
        NUP = 0x00000040,
        DisplayOrientation = 0x00000080,
        Copies = 0x00000100,
        DefaultSource = 0x00000200,
        PrintQuality = 0x00000400,
        Color = 0x00000800,
        Duplex = 0x00001000,
        YResolution = 0x00002000,
        TTOption = 0x00004000,
        Collate = 0x00008000,
        FormName = 0x00010000,
        LogPixels = 0x00020000,
        BitsPerPixel = 0x00040000,
        PelsWidth = 0x00080000,
        PelsHeight = 0x00100000,
        DisplayFlags = 0x00200000,
        DisplayFrequency = 0x00400000,
        ICMMethod = 0x00800000,
        ICMIntent = 0x01000000,
        MediaType = 0x02000000,
        DitherType = 0x04000000,
        PanningWidth = 0x08000000,
        PanningHeight = 0x10000000,
        DisplayFixedOutput = 0x20000000
    }

    const int DMDO_DEFAULT = 0;
    const int DMDO_90 = 1;
    const int DMDO_180 = 2;
    const int DMDO_270 = 3;

    const int ENUM_CURRENT_SETTINGS = -1;

    [DllImport("user32.dll")]
    static extern DISP_CHANGE ChangeDisplaySettingsEx(string lpszDeviceName, ref DEVMODE lpDevMode, IntPtr hwnd, DisplaySettingsFlags dwflags, IntPtr lParam);

    [DllImport("user32.dll")]
    static extern bool EnumDisplayDevices(string? lpDevice, uint iDevNum, ref DISPLAY_DEVICE lpDisplayDevice, uint dwFlags);

    [DllImport("user32.dll", CharSet = CharSet.Ansi)]
    static extern int EnumDisplaySettings(string lpszDeviceName, int iModeNum, ref DEVMODE lpDevMode);

    public enum Orientation
    {
        LANDSCAPE,
        PORTRAIT_FLIPPED,
        LANDSCAPE_FLIPPED,
        PORTRAIT
    }

    // Used for setting the actual orientation
    private static Dictionary<Orientation, int> orientationToDM = new()
    {
        [Orientation.LANDSCAPE] = DMDO_DEFAULT,
        [Orientation.PORTRAIT_FLIPPED] = DMDO_270,
        [Orientation.LANDSCAPE_FLIPPED] = DMDO_180,
        [Orientation.PORTRAIT] = DMDO_90
    };

    public static bool Rotate(uint displayID, Orientation orientation)
    {
        var disp = new DISPLAY_DEVICE();
        var devmode = new DEVMODE();

        disp.cb = Marshal.SizeOf(disp);

        // Check invalid displayIDs
        if (displayID == 0 || !EnumDisplayDevices(null, displayID - 1, ref disp, 0))
            return false;

        if (EnumDisplaySettings(disp.DeviceName, ENUM_CURRENT_SETTINGS, ref devmode) == 0)
            return false;

        // Flip display width/height values if needed
        if ((devmode.dmDisplayOrientation + (int)orientation) % 2 == 1)
            (devmode.dmPelsWidth, devmode.dmPelsHeight) = (devmode.dmPelsHeight, devmode.dmPelsWidth);

        devmode.dmDisplayOrientation = orientationToDM[orientation];

        var result = ChangeDisplaySettingsEx(disp.DeviceName, ref devmode, IntPtr.Zero, DisplaySettingsFlags.CDS_UPDATEREGISTRY, IntPtr.Zero);

        return result == DISP_CHANGE.Successful;
    }

    public static List<uint> GetDisplayIDs() {
        var ids = new List<uint>();

        for (uint i = 0; i < 64; ++i) {
            var disp = new DISPLAY_DEVICE();

            disp.cb = Marshal.SizeOf(disp);

            if (EnumDisplayDevices(null, i, ref disp, 0))
                if (disp.StateFlags.HasFlag(DisplayDeviceStateFlags.AttachedToDesktop))
                    ids.Add(i + 1);
        }

        return ids;
    }
}