Powershell for getting the currently configured resolution from all active monitors

AllResolutions.ps1

$pinvokeCode = @" 
using System; 
using System.Runtime.InteropServices; 
using System.Collections.Generic;
namespace Resolution 
{ 
    [StructLayout(LayoutKind.Sequential)] 
    public struct DEVMODE1 
    { 
        [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 dmLogPixels; 
        public short dmBitsPerPel; 
        public int dmPelsWidth; 
        public int dmPelsHeight; 
        public int dmDisplayFlags; 
        public int dmDisplayFrequency; 
        public int dmICMMethod; 
        public int dmICMIntent; 
        public int dmMediaType; 
        public int dmDitherType; 
        public int dmReserved1; 
        public int dmReserved2; 
        public int dmPanningWidth; 
        public int dmPanningHeight; 
    }; 
	
	[Flags()]
	public 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
	}
	[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi)]
	public 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;
	}
    class User_32 
    { 
        [DllImport("user32.dll")] 
        public static extern int EnumDisplaySettings(string deviceName, int modeNum, ref DEVMODE1 devMode); 
        [DllImport("user32.dll")] 
        public static extern int ChangeDisplaySettings(ref DEVMODE1 devMode, int flags); 
		[DllImport("user32.dll")]
		public static extern bool EnumDisplayDevices(string lpDevice, uint iDevNum, ref DISPLAY_DEVICE lpDisplayDevice, uint dwFlags);
        public const int ENUM_CURRENT_SETTINGS = -1; 
        public const int CDS_UPDATEREGISTRY = 0x01; 
        public const int CDS_TEST = 0x02; 
        public const int DISP_CHANGE_SUCCESSFUL = 0; 
        public const int DISP_CHANGE_RESTART = 1; 
        public const int DISP_CHANGE_FAILED = -1; 
    } 
    public class Displays
    {
		public static IList<string> GetDisplayNames()
		{
			var returnVals = new List<string>();
			for(var x=0U; x<1024; ++x)
			{
				DISPLAY_DEVICE outVar = new DISPLAY_DEVICE();
				outVar.cb = (short)Marshal.SizeOf(outVar);
				if(User_32.EnumDisplayDevices(null, x, ref outVar, 1U))
				{
					returnVals.Add(outVar.DeviceName);
				}
			}
			return returnVals;
		}
		
		public static string GetCurrentResolution(string deviceName)
        {
            string returnValue = null;
            DEVMODE1 dm = GetDevMode1();
            if (0 != User_32.EnumDisplaySettings(deviceName, User_32.ENUM_CURRENT_SETTINGS, ref dm))
            {
                returnValue = dm.dmPelsWidth + "," + dm.dmPelsHeight;
            }
            return returnValue;
        }
		
		public static IList<string> GetResolutions()
		{
			var displays = GetDisplayNames();
			var returnValue = new List<string>();
			foreach(var display in displays)
			{
				returnValue.Add(GetCurrentResolution(display));
			}
			return returnValue;
		}
		
        private static DEVMODE1 GetDevMode1() 
        { 
            DEVMODE1 dm = new DEVMODE1(); 
            dm.dmDeviceName = new String(new char[32]); 
            dm.dmFormName = new String(new char[32]); 
            dm.dmSize = (short)Marshal.SizeOf(dm); 
            return dm; 
        } 
    }
} 
"@
Add-Type $pinvokeCode
[Resolution.Displays]::GetResolutions();

Yeah, it's not very well named; it gets all current resolutions from all monitors configured. The original use-case was for finding machines with odd-ball non-standard additional monitors plugged in or buggy drivers that have set the wrong resolution; so it's aimed totally around multi-monitor configurations, rather than resolution discovery of a single monitor.

It should provide a good base for finding out what you want though as I'd imagine the WinAPI is basically the same.

👍 indeed, thanks for the great starting point!