DisplaySettings

0.0.1

CDS.cs

namespace cds
{
    using System;
    using System.Runtime.InteropServices;

    [StructLayout(LayoutKind.Explicit)]
    public struct DEVMODE
    {
        [FieldOffset(102)]
        public short dmLogPixels;
        [FieldOffset(104)]
        public int dmBitsPerPel;
        [FieldOffset(108)]
        public int dmPelsWidth;
        [FieldOffset(112)]
        public int dmPelsHeight;
        [FieldOffset(116)]
        public int dmDisplayFlags;
        [FieldOffset(120)]
        public int dmDisplayFrequency;
    }


    // https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-changedisplaysettingsa
    public class Helper
    {
        public static DEVMODE GetDisplaySettings()
        {
            // #define ENUM_CURRENT_SETTINGS ((DWORD)-1)
            // #define ENUM_REGISTRY_SETTINGS ((DWORD)-2)
            var devMode = new DEVMODE();

            // A NULL value specifies the current display device on the computer on which the calling thread is running.
            var retCode = EnumDisplaySettings(null, -1, ref devMode);
            if (retCode == 0)
            {
                throw new Exception("can't get resolution from win api");
            }

            return devMode;
        }

        public static string ChangeDisplaySettings(int width, int height, int flags)
        {
            // /* Return values for ChangeDisplaySettings */
            // #define DISP_CHANGE_SUCCESSFUL 0
            // #define DISP_CHANGE_RESTART 1
            // #define DISP_CHANGE_FAILED -1
            // #define DISP_CHANGE_BADMODE -2
            // #define DISP_CHANGE_NOTUPDATED -3
            // #define DISP_CHANGE_BADFLAGS -4
            // #define DISP_CHANGE_BADPARAM -5
            // #if(_WIN32_WINNT >= 0x0501)
            // #define DISP_CHANGE_BADDUALVIEW -6
            // #endif /* _WIN32_WINNT >= 0x0501 */

            var devMode = GetDisplaySettings();

            devMode.dmPelsWidth = width;
            devMode.dmPelsHeight = height;

            var res = ChangeDisplaySettings(ref devMode, flags);
            switch (res)
            {
                case 0:
                    return "The settings change was successful.";
                case 1:
                    return "The computer must be restarted for the graphics mode to work.";
                case -1:
                    return "The display driver failed the specified graphics mode.";
                case -2:
                    return "The graphics mode is not supported.";
                case -3:
                    return "Unable to write settings to the registry.";
                case -4:
                    return "An invalid set of flags was passed in.";
                case -5:
                    return "An invalid parameter was passed in. This can include an invalid flag or combination of flags.";
                case -6:
                    return "The settings change was unsuccessful because the system is DualView capable.";
                default:
                    return $"unknow return code: {res}";
            }
        }

        [DllImport("user32.dll")]
        static extern int EnumDisplaySettings(string deviceName, int modeNum, ref DEVMODE devMode);

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

        public class Flags
        {
            // #define CDS_UPDATEREGISTRY 0x00000001
            // #define CDS_TEST 0x00000002
            // #define CDS_FULLSCREEN 0x00000004
            // #define CDS_GLOBAL 0x00000008
            // #define CDS_SET_PRIMARY 0x00000010
            // #define CDS_RESET 0x40000000
            // #define CDS_NORESET 0x10000000

            public const int CDS_UPDATEREGISTRY = 0x01;
            public const int CDS_TEST = 0x02;
            public const int CDS_FULLSCREEN = 0x04;
            public const int CDS_GLOBAL = 0x08;
            public const int CDS_SET_PRIMARY = 0x10;
            public const int CDS_RESET = 0x40000000;
            public const int CDS_NORESET = 0x10000000;
        }
    }
}