C#•6mo ago

Capturing multiple displays scaling information

I have managed to code a function that semi works in terms of capturing all displays scaling. The only issue is, it captures the default monitors scaling only. The function I found and changed slightly is below:

c#
        public static float GetDPIScaling(int monitorIndex)
        {
            //IntPtr monitorHwnd = GetMonitorHandle(monitorIndex);
            IntPtr monitorHwnd = new IntPtr(0);
            //Int64 numberTemp = monitorHwnd.ToInt64();
            Graphics g = Graphics.FromHwnd(monitorHwnd);
            IntPtr desktop = g.GetHdc();

            int LogicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.VERTRES);
            int PhysicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.DESKTOPVERTRES);

            return (float)PhysicalScreenHeight / (float)LogicalScreenHeight;
        }

c#
        public static float GetDPIScaling(int monitorIndex)
        {
            //IntPtr monitorHwnd = GetMonitorHandle(monitorIndex);
            IntPtr monitorHwnd = new IntPtr(0);
            //Int64 numberTemp = monitorHwnd.ToInt64();
            Graphics g = Graphics.FromHwnd(monitorHwnd);
            IntPtr desktop = g.GetHdc();

            int LogicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.VERTRES);
            int PhysicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.DESKTOPVERTRES);

            return (float)PhysicalScreenHeight / (float)LogicalScreenHeight;
        }

With this, it returns 1.25 for 125% scaling. If I change my default monitor to 150%, it will return 1.5. So it does return the scaling. The only issue I have now is passing the monitor index through as a parameter. And then using it in the following way

c#
IntPtr monitorHwnd = new IntPtr(monitorIndex);

c#
IntPtr monitorHwnd = new IntPtr(monitorIndex);

This will throw an error once monitor index is not 0. The error shows the following:

Exception thrown: 'System.OutOfMemoryException' in System.Drawing.dll
An unhandled exception of type 'System.OutOfMemoryException' occurred in System.Drawing.dll
Out of memory.

Exception thrown: 'System.OutOfMemoryException' in System.Drawing.dll
An unhandled exception of type 'System.OutOfMemoryException' occurred in System.Drawing.dll
Out of memory.

According to my understanding of the program. The value of 'monitorHwnd ' will be something like

0x0000

0x0000

when it is 0 and

0x0001

0x0001

when it is 1 and so on. This is how I call my function:

c#
foreach (var monitor in monitorList)
{
    float dpiScaling = GetDPIScaling(monitor.Index);
    string scalingString = (dpiScaling * 100).ToString();
    Console.WriteLine($"DPI Scaling for Monitor {monitor.Index}: {scalingString}%");
}

c#
foreach (var monitor in monitorList)
{
    float dpiScaling = GetDPIScaling(monitor.Index);
    string scalingString = (dpiScaling * 100).ToString();
    Console.WriteLine($"DPI Scaling for Monitor {monitor.Index}: {scalingString}%");
}

The overall reason for me needing the scaling is for a feature I am making that will take a screenshot. This is one of those functions to make the app work on multiple displays.

16 Replies

Jester•6mo ago

ok ill take a look

SparkyCracked•6mo ago

Thank you!!! I've been working on it for the past 3 days. This is the closest I have gotten. When we pass 0 into the pointer it does give 125% for all screens which as you said may be due to the null hwnd

Jester•6mo ago

i think you could use https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-enumdisplaymonitors and https://learn.microsoft.com/en-us/windows/win32/api/shellscalingapi/nf-shellscalingapi-getdpiformonitor

EnumDisplayMonitors function (winuser.h) - Win32 apps

The EnumDisplayMonitors function enumerates display monitors (including invisible pseudo-monitors associated with the mirroring drivers) that intersect a region formed by the intersection of a specified clipping rectangle and the visible region of a device context. EnumDisplayMonitors calls an application-defined MonitorEnumProc callback functio...

GetDpiForMonitor function (shellscalingapi.h) - Win32 apps

Queries the dots per inch (dpi) of a display.

SparkyCracked•6mo ago

I was able to fetch the screens Monitor \.\DISPLAY1: HWND = 65539 Monitor \.\DISPLAY2: HWND = 65541 Monitor \.\DISPLAY3: HWND = 65537

Jester•6mo ago

EnumDisplayMonitors(null, null, your delegate, 0) in your delegate GetDpiForMonitor for each handle it gets

SparkyCracked•6mo ago

Ok, will give this a try in about 5 min Wanna get coffee real quick Can I ask, do you mind trying to assist me with the existing fuction.

c#
public static float GetDPIScaling(IntPtr monitorHwnd)
{
    //IntPtr monitorHwnd = GetMonitorHandle(monitorIndex);
    //IntPtr monitorHwnd = new IntPtr(monitorIndex); // You need to obtain the monitor's HWND based on the monitorIndex, or you can pass the correct HWND as an argument.
    //Int64 numberTemp = monitorHwnd.ToInt64();
    Graphics g = Graphics.FromHwnd(monitorHwnd);
    IntPtr desktop = g.GetHdc();

    int LogicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.VERTRES);
    int PhysicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.DESKTOPVERTRES);

    return (float)PhysicalScreenHeight / (float)LogicalScreenHeight;
}

c#
public static float GetDPIScaling(IntPtr monitorHwnd)
{
    //IntPtr monitorHwnd = GetMonitorHandle(monitorIndex);
    //IntPtr monitorHwnd = new IntPtr(monitorIndex); // You need to obtain the monitor's HWND based on the monitorIndex, or you can pass the correct HWND as an argument.
    //Int64 numberTemp = monitorHwnd.ToInt64();
    Graphics g = Graphics.FromHwnd(monitorHwnd);
    IntPtr desktop = g.GetHdc();

    int LogicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.VERTRES);
    int PhysicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.DESKTOPVERTRES);

    return (float)PhysicalScreenHeight / (float)LogicalScreenHeight;
}

I changed it to look like this now. It now uses the hWnd. So it handles that window

Jester•6mo ago

you should dispose the graphics and hdc at the end

SparkyCracked•6mo ago

Ok I still get the issue

Out of Memory

Out of Memory

This is so weird I get it here Graphics g = Graphics.FromHwnd(monitorHwnd);

Jester•6mo ago

SparkyCracked•6mo ago

Pointers are new to me so it's something I don't understand

Jester•6mo ago

its also a really old windows api so it is weird idk how this happened

SparkyCracked•6mo ago

It may be the invalid window type...in terms of hwnd. But It fetches this hwnd so not sure... After evaluating the variables, this is the variable value of monitorHwnd = 0x00010003 Inside graphics g

Jester•6mo ago

im also busy doing other stuff now so i cant help you too much rn

SparkyCracked•6mo ago

Ok thats fine. You provided a lot of help already. I will keep trying and will let you know of my findings as I make progress Managed to solve this. Thank you very much @297 лаyс ынтил hаллоwээн 👻 A problem that took 4 days...my word when

Jester•6mo ago

issue

takes a while to get familiar with the win32 api

SparkyCracked•6mo ago

Yeah it does, I can agree

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Capturing multiple displays scaling information