GetRefreshRate.cs

using System;
using System.Runtime.InteropServices;

namespace OaktreeLab.Utils {
    internal class DisplayHelper {
        public static uint GetRefreshRate( IntPtr hWnd ) {
            IntPtr hmonitor = MonitorFromWindow( hWnd, MONITOR_DEFAULTTONEAREST );
            MONITORINFOEXW monitorInfo = new MONITORINFOEXW();
            monitorInfo.cbSize = (uint)Marshal.SizeOf<MONITORINFOEXW>();
            GetMonitorInfoW( hmonitor, ref monitorInfo );
            DEVMODEW devMode = new DEVMODEW();
            devMode.dmSize = (ushort)Marshal.SizeOf<DEVMODEW>();
            EnumDisplaySettingsW( monitorInfo.szDevice, ENUM_CURRENT_SETTINGS, out devMode );
            return devMode.dmDisplayFrequency;
        }

        private const uint MONITOR_DEFAULTTONEAREST = 2;

        [DllImport( "user32.dll", SetLastError = false )]
        private static extern IntPtr MonitorFromWindow( IntPtr hWnd, uint dwFlags );

        [StructLayout( LayoutKind.Sequential )]
        private struct RECT {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }

        [StructLayout( LayoutKind.Sequential, CharSet = CharSet.Unicode )]
        private unsafe struct MONITORINFOEXW {
            public uint cbSize;
            public RECT rcMonitor;
            public RECT rcWork;
            public uint dwFlags;

            [MarshalAs( UnmanagedType.ByValTStr, SizeConst = 32 )]
            public string szDevice;
        }

        [DllImport( "user32.dll", SetLastError = false, CharSet = CharSet.Unicode )]
        [return: MarshalAs( UnmanagedType.Bool )]
        private static extern bool GetMonitorInfoW( IntPtr hMonitor, ref MONITORINFOEXW lpmi );

        private const uint ENUM_CURRENT_SETTINGS = unchecked((uint)-1);

        [DllImport( "user32.dll", SetLastError = false, CharSet = CharSet.Unicode )]
        [return: MarshalAs( UnmanagedType.Bool )]
        private static extern bool EnumDisplaySettingsW( [MarshalAs( UnmanagedType.LPWStr )] string lpszDeviceName, uint iModeNum, out DEVMODEW lpDevMode );

        [StructLayout( LayoutKind.Sequential, CharSet = CharSet.Unicode )]
        private struct DEVMODEW {
            [MarshalAs( UnmanagedType.ByValTStr, SizeConst = 32 )]
            public string dmDeviceName;

            public ushort dmSpecVersion;
            public ushort dmDriverVersion;
            public ushort dmSize;
            public ushort dmDriverExtra;
            public uint dmFields;

            public int dmPositionX;
            public int dmPositionY;
            public uint dmDisplayOrientation;
            public uint dmDisplayFixedOutput;

            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 dmLogPixels;
            public uint dmBitsPerPel;
            public uint dmPelsWidth;
            public uint dmPelsHeight;

            public uint dmNupOrDisplayFlags;
            public uint dmDisplayFrequency;

            public uint dmICMMethod;
            public uint dmICMIntent;
            public uint dmMediaType;
            public uint dmDitherType;
            public uint dmReserved1;
            public uint dmReserved2;
            public uint dmPanningWidth;
            public uint dmPanningHeight;
        }
    }
}