C# - How to get real screen resolution in multiple monitors context?

Question

For one of my application (write in WPF), I need to get some informations about monitors : Current resolution, scaling factor and real resolution.

I know this question has been asked many times but I'm not able to find a good answer in all SO questions that talked about that...

In my case for example, I have 3 monitors placed in this order :

• Monitor 1 (integrated laptop screen) : 1920x1080, scaled at 125%
• Monitor 2 (LG 22") : 1920x1080, scaled at 100% (PRIMARY MONITOR)
• Monitor 3 (LG 22") : 1920x1080, scaled at 100%

When using System.Windows.Forms.Screen.AllScreens, I obtain a resolution of 1536x864 for my first monitor. It's OK because 1536*1.25 = 1920. But i'm not able to find either the 1.25 or the 1920 ^^ (for the other monitors it's OK because they're scaled at 100%).

But if I set monitor 1 to be primary I can obtain it's real resolution but for monitor 2 and 3 I obtain 2400*1350... It's 1920x1080 multiply by the primary monitor's scaling factor : 1.25

It's been 2 days since I try many ways. I've tried AllScreens in Windows.Forms. In WinAPI I've tried EnumDisplayMonitors, GetDeviceCaps, GetScaleFactorForMonitor, GetDpiForMonitor... Everything always give me a 100% scaling factor or a DPI of 96 for my first monitor which is an error...

Do you know a secure way to obtain these informations ? In WMI, in registry, etc...

Thanks for your help !

(PS : if needed I can provide code sample of what I tried but I don't want to flood this first post)

EDIT : I forgot to mention that I need to obtain these informations without any visual app (my DLL is called from a VB application)

Answer 1

I have almost exactly the same setup. I was able to get the real resolution by calling EnumDisplaySettings using p/invoke.

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

const int ENUM_CURRENT_SETTINGS = -1;

foreach (Screen screen in Screen.AllScreens)
{
    var dm = new DEVMODE();
    dm.dmSize = (short)Marshal.SizeOf(typeof(DEVMODE));
    EnumDisplaySettings(screen.DeviceName, ENUM_CURRENT_SETTINGS, ref dm);

    Console.WriteLine($"Device: {screen.DeviceName}");
    Console.WriteLine($"Real Resolution: {dm.dmPelsWidth}x{dm.dmPelsHeight}");
    Console.WriteLine($"Virtual Resolution: {screen.Bounds.Width}x{screen.Bounds.Height}");
    Console.WriteLine();
}

[DllImport("user32.dll")]
static extern bool EnumDisplaySettings(string lpszDeviceName, int iModeNum, ref DEVMODE lpDevMode);

[StructLayout(LayoutKind.Sequential)]
public struct DEVMODE
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 0x20)]
    public string dmDeviceName;
    public short dmSpecVersion;
    public short dmDriverVersion;
    public short dmSize;
    public short dmDriverExtra;
    public int dmFields;
    public int dmPositionX;
    public int dmPositionY;
    public ScreenOrientation dmDisplayOrientation;
    public int dmDisplayFixedOutput;
    public short dmColor;
    public short dmDuplex;
    public short dmYResolution;
    public short dmTTOption;
    public short dmCollate;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 0x20)]
    public string dmFormName;
    public short dmLogPixels;
    public int 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;
}

And the output:

Device: \\.\DISPLAY1
Real Resolution: 1920x1080
Virtual Resolution: 1536x864

Device: \\.\DISPLAY2
Real Resolution: 1920x1080
Virtual Resolution: 1920x1080

Device: \\.\DISPLAY3
Real Resolution: 1920x1080
Virtual Resolution: 1920x1080

https://stackoverflow.com/a/36864741/987968 http://pinvoke.net/default.aspx/user32/EnumDisplaySettings.html?diff=y