ScreenMgmt

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;

namespace ScreenMgmtLibrary
{
    #region Structures
    [StructLayout(LayoutKind.Sequential)]
    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;

        public DISPLAY_DEVICE(int flags)
        {
            cb = 0;
            StateFlags = flags;
            DeviceName = new string((char)32, 32);
            DeviceString = new string((char)32, 128);
            DeviceID = new string((char)32, 128);
            DeviceKey = new string((char)32, 128);
            cb = Marshal.SizeOf(this);
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct DEVMODE
    {
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
        public string dmDeviceName;
        public short dmSpecVersion;
        public short dmDriverVersion;
        public short dmSize;
        public short dmDriverExtra;
        public int dmFields;
        public short dmOrientation;
        public short dmPaperSize;
        public short dmPaperLength;
        public short dmPaperWidth;
        public short dmScale;
        public short dmCopies;
        public short dmDefaultSource;
        public short dmPrintQuality;
        public short dmColor;
        public short dmDuplex;
        public short dmYResolution;
        public short dmTTOption;
        public short dmCollate;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
        public string dmFormName;
        public short dmUnusedPadding;
        public short dmBitsPerPel;
        public int dmPelsWidth;
        public int dmPelsHeight;
        public int dmDisplayFlags;
        public int dmDisplayFrequency;
    }
    #endregion

    public static class Screenmgmt
    {
        #region DLLImports
        [DllImport("User32.dll")]
        private static extern bool EnumDisplayDevices(IntPtr lpDevice, int iDevNum, ref DISPLAY_DEVICE lpDisplayDevice, int dwFlags);

        [DllImport("User32.dll")]
        private static extern bool EnumDisplaySettings(string devName, int modeNum, ref DEVMODE devMode);

        [DllImport("user32.dll")]
        private static extern int ChangeDisplaySettings(ref DEVMODE devMode, int flags);
        #endregion

        /// <summary>
        /// Change the resolution of <param name="devNum"> by <param name="modeNum">
        /// </summary>
        static public void ChangeResolution(int devNum, int modeNum)
        {
            DEVMODE d = GetDevmode(devNum, modeNum);
            if (d.dmBitsPerPel != 0 & d.dmPelsWidth != 0 & d.dmPelsHeight != 0)
                ChangeDisplaySettings(ref d, 0);
        }

        #region Modes
        /// <summary>
        /// Return a list of available modes
        /// </summary>
        static public List<string> EnumModes(int devNum)
        {
            List<string> modes = new List<string>();
            string devName = GetDeviceName(devNum);
            DEVMODE devMode = new DEVMODE();
            int modeNum = 0;
            bool result = true;
            do
            {
                result = EnumDisplaySettings(devName, modeNum, ref devMode);
                if (result)
                {
                    string item = DevmodeToString(devMode);
                    modes.Add(item);
                }
                modeNum++;
            } while (result);
            return modes;
        }

        /// <summary>
        /// Get the actual mode of the device <param name="devNum">
        /// </summary>
        static public DEVMODE GetDevmode(int devNum, int modeNum)
        {
            DEVMODE devMode = new DEVMODE();
            string devName = GetDeviceName(devNum);
            EnumDisplaySettings(devName, modeNum, ref devMode);
            return devMode;
        }

        /// <summary>
        /// Convert to a human readable format a devmode, for eg : to ask for the user to choose one
        /// </summary>
        static public string DevmodeToString(DEVMODE devMode)
        {
            return devMode.dmPelsWidth.ToString() + " x " + devMode.dmPelsHeight.ToString() + ", "
                + devMode.dmBitsPerPel.ToString() + " bits, "
                + devMode.dmDisplayFrequency.ToString() + " Hz";
        }
        #endregion

        #region Devices
        /// <summary>
        /// Return a list of string of all the available devices
        /// </summary>
        static public List<string> EnumDevices()
        {
            List<string> devices = new List<string>();

            DISPLAY_DEVICE d = new DISPLAY_DEVICE(0);

            int devNum = 0;
            bool result;
            do
            {
                result = EnumDisplayDevices(IntPtr.Zero, devNum, ref d, 0);
                if (result)
                {
                    string item = DeviceToString(d, devNum);
                    devices.Add(item);
                }
                devNum++;
            } while (result);
            return devices;
        }

        /// <summary>
        /// Convert a display device to a human readable format
        /// </summary>
        static public string DeviceToString(DISPLAY_DEVICE d, int devNum)
        {
            string r = devNum.ToString() + ". " + d.DeviceString.Trim();
            if ((d.StateFlags & 4) != 0) r += " - MASTER";
            return r;
        }

        /// <summary>
        /// Get the name of a device passed in argument
        /// </summary>
        static public string GetDeviceName(int devNum)
        {
            DISPLAY_DEVICE d = new DISPLAY_DEVICE(0);
            bool result = EnumDisplayDevices(IntPtr.Zero, devNum, ref d, 0);
            return (result ? d.DeviceName.Trim() : "#error#");
        }

        /// <summary>
        /// Get the name of the Main Device
        /// </summary>
        static public bool MainDevice(int devNum)
        {
            DISPLAY_DEVICE d = new DISPLAY_DEVICE(0);
            if (EnumDisplayDevices(IntPtr.Zero, devNum, ref d, 0))
                return ((d.StateFlags & 4) != 0);
            return false;
        }
        #endregion

        #region Search
        /// <summary>
        /// Return index of actuals modes
        /// </summary>
        static public List<int> SearchActualResolutionModes()
        {
            List<int> r = new List<int>();
            int i = 0;
            while (MainDevice(i) == false) i++;
            r.Add(i);

            DEVMODE current = GetDevmode(i, -1);
            r.Add(EnumModes(r.First()).IndexOf(DevmodeToString(current)));

            return r;
        }

        /// <summary>
        /// Return index for the mode of the device passed on argument
        /// </summary>
        static public int SearchSettingsString(string toFind, int devNum)
        {
            List<string> modes = Screenmgmt.EnumModes(devNum);
            int i = 0;
            foreach (string s in modes)
            {
                if (s == toFind)
                    return i;
                else
                    i++;
            }
            return -1;
        }

        /// <summary>
        /// Return devmode of the mode for the device passed on argument
        /// </summary>
        static public DEVMODE SearchSettingsStruct(string toFind, int devNum)
        {
            string devName = GetDeviceName(devNum);
            DEVMODE devMode = new DEVMODE();
            int modeNum = 0;
            bool result = true;
            do
            {
                result = EnumDisplaySettings(devName, modeNum, ref devMode);
                if (result)
                {
                    string item = DevmodeToString(devMode);
                    if (item == toFind)
                        return devMode;
                }
                modeNum++;
            } while (result);
            return devMode;
        }
        #endregion
    }
}