ActuallyChangingResolution.cs

using System.Runtime.InteropServices;

namespace Resolutioner
{

    // based on https://www.codeproject.com/Articles/36664/Changing-Display-Settings-Programmatically
    // Copyright Mohammad Elsheimy 2009, Mika Feiler 2022
    // CPL 1.0 License http://www.opensource.org/licenses/cpl1.0.php
    // The Common Public License Version 1.0 (CPL)
    public class ActuallyChangingResolution
    {
        [StructLayout(LayoutKind.Sequential,
            CharSet = CharSet.Ansi)]
        struct DEVMODE
        {
            // You can define the following constant
            // but OUTSIDE the structure because you know
            // that size and layout of the structure
            // is very important
            // CCHDEVICENAME = 32 = 0x50
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
            public string dmDeviceName;
            // In addition you can define the last character array
            // as following:
            //[MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
            //public Char[] dmDeviceName;

            // After the 32-bytes array
            [MarshalAs(UnmanagedType.U2)]
            public UInt16 dmSpecVersion;

            [MarshalAs(UnmanagedType.U2)]
            public UInt16 dmDriverVersion;

            [MarshalAs(UnmanagedType.U2)]
            public UInt16 dmSize;

            [MarshalAs(UnmanagedType.U2)]
            public UInt16 dmDriverExtra;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmFields;

            [MarshalAs(UnmanagedType.I4)]
            public int dmPositionX;
            [MarshalAs(UnmanagedType.I4)]
            public int dmPositionY;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmDisplayOrientation;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmDisplayFixedOutput;

            [MarshalAs(UnmanagedType.I2)]
            public Int16 dmColor;

            [MarshalAs(UnmanagedType.I2)]
            public Int16 dmDuplex;

            [MarshalAs(UnmanagedType.I2)]
            public Int16 dmYResolution;

            [MarshalAs(UnmanagedType.I2)]
            public Int16 dmTTOption;

            [MarshalAs(UnmanagedType.I2)]
            public Int16 dmCollate;

            // CCHDEVICENAME = 32 = 0x50
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
            public string dmFormName;
            // Also can be defined as
            //[MarshalAs(UnmanagedType.ByValArray,
            //    SizeConst = 32, ArraySubType = UnmanagedType.U1)]
            //public Byte[] dmFormName;

            [MarshalAs(UnmanagedType.U2)]
            public UInt16 dmLogPixels;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmBitsPerPel;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmPelsWidth;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmPelsHeight;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmDisplayFlags;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmDisplayFrequency;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmICMMethod;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmICMIntent;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmMediaType;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmDitherType;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmReserved1;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmReserved2;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmPanningWidth;

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dmPanningHeight;
        }

        [DllImport("User32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        static extern Boolean EnumDisplaySettings(
            [param: MarshalAs(UnmanagedType.LPTStr)]
            string lpszDeviceName,
            [param: MarshalAs(UnmanagedType.U4)]
            iModeNumEnum iModeNum,
            [In, Out]
            ref DEVMODE lpDevMode);
        
        enum iModeNumEnum
        {
            ENUM_CURRENT_SETTINGS = -1,
            ENUM_REGISTRY_SETTINGS = -2
        }

        [DllImport("User32.dll")]
        [return: MarshalAs(UnmanagedType.I4)]
        static extern int ChangeDisplaySettings(
            [In, Out]
            ref DEVMODE lpDevMode,
            [param: MarshalAs(UnmanagedType.U4)]
            uint dwflags);

        public enum dispChangeResult
        {
            SUCCESSFUL = 0, // Indicates that the function succeeded.
            BADMODE = -2, // The graphics mode is not supported.
            _FAILED = -1, // The display driver failed the specified graphics mode.
            RESTART = 1 // The computer must be restarted for the graphics mode to work.
        }
        public static dispChangeResult ChangeDisplaySettings(int width, int height)
        {
            DEVMODE originalMode = new DEVMODE();
            originalMode.dmSize =
                (ushort)Marshal.SizeOf(originalMode);
            // Retrieving current settings
            // to edit them
#pragma warning disable CS8625 // Nie można przekonwertować literału o wartości null na nienullowalny typ referencyjny.
            EnumDisplaySettings(null,
#pragma warning restore CS8625 // Nie można przekonwertować literału o wartości null na nienullowalny typ referencyjny.
                iModeNumEnum.ENUM_CURRENT_SETTINGS,
                ref originalMode);

            // Making a copy of the current settings
            // to allow reseting to the original mode
            DEVMODE newMode = originalMode;

            // Changing the settings
            newMode.dmPelsWidth = (uint)width;
            newMode.dmPelsHeight = (uint)height;

            // Capturing the operation result
            int result =
                ChangeDisplaySettings(ref newMode, 0);

            return (dispChangeResult) result;
        }
    }
}