Display.cs

using System;
using System.Runtime.InteropServices;

public class Display {
    public enum Orientations {
        DEGREES_CW_0 = 0,
        DEGREES_CW_90 = 3,
        DEGREES_CW_180 = 2,
        DEGREES_CW_270 = 1
    }

    public static bool Rotate(uint DisplayNumber, Orientations Orientation) {
        if (DisplayNumber == 0)
            throw new ArgumentOutOfRangeException("DisplayNumber", DisplayNumber, "First display is 1.");

        bool result = false;
        DISPLAY_DEVICE d = new DISPLAY_DEVICE();
        DEVMODE dm = new DEVMODE();
        d.cb = Marshal.SizeOf(d);

        if (!NativeMethods.EnumDisplayDevices(null, DisplayNumber - 1, ref d, 0))
            throw new ArgumentOutOfRangeException("DisplayNumber", DisplayNumber, "Number is greater than connected displays.");

        if (0 != NativeMethods.EnumDisplaySettings(
            d.DeviceName, NativeMethods.ENUM_CURRENT_SETTINGS, ref dm)) {
            if ((dm.dmDisplayOrientation + (int)Orientation) % 2 == 1) // Need to swap height and width?
            {
                int temp = dm.dmPelsHeight;
                dm.dmPelsHeight = dm.dmPelsWidth;
                dm.dmPelsWidth = temp;
            }

            switch (Orientation) {
                case Orientations.DEGREES_CW_90:
                    dm.dmDisplayOrientation = NativeMethods.DMDO_270;
                    break;
                case Orientations.DEGREES_CW_180:
                    dm.dmDisplayOrientation = NativeMethods.DMDO_180;
                    break;
                case Orientations.DEGREES_CW_270:
                    dm.dmDisplayOrientation = NativeMethods.DMDO_90;
                    break;
                case Orientations.DEGREES_CW_0:
                    dm.dmDisplayOrientation = NativeMethods.DMDO_DEFAULT;
                    break;
                default:
                    break;
            }

            DISP_CHANGE ret = NativeMethods.ChangeDisplaySettingsEx(
                d.DeviceName, ref dm, IntPtr.Zero,
                DisplaySettingsFlags.CDS_UPDATEREGISTRY, IntPtr.Zero);

            result = ret == 0;
        }

        return result;
    }

    public static void ResetAllRotations() {
        try {
            uint i = 0;
            while (++i <= 64) {
                Rotate(i, Orientations.DEGREES_CW_0);
            }
        } catch (ArgumentOutOfRangeException ex) {
            // Everything is fine, just reached the last display
        }
    }
}

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

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

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

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

    public const int ENUM_CURRENT_SETTINGS = -1;

}

// See: https://msdn.microsoft.com/en-us/library/windows/desktop/dd183565(v=vs.85).aspx
[StructLayout(LayoutKind.Explicit, CharSet = CharSet.Ansi)]
internal 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;
}

// See: https://msdn.microsoft.com/en-us/library/windows/desktop/dd183569(v=vs.85).aspx
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
internal 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;
}

// See: https://msdn.microsoft.com/de-de/library/windows/desktop/dd162807(v=vs.85).aspx
[StructLayout(LayoutKind.Sequential)]
internal struct POINTL {
    long x;
    long y;
}

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

// http://www.pinvoke.net/default.aspx/Enums/DisplayDeviceStateFlags.html
[Flags()]
internal 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
}

// http://www.pinvoke.net/default.aspx/user32/ChangeDisplaySettingsFlags.html
[Flags()]
internal 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()]
internal 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
}