All ways to get DPI in Windows using Dotnet Framework, Native APIs & Registry.

18 Oct 2023 | ପ୍ରୋ ନିୟନ ୨୬୭(proneon267)

The following are all the ways to get the DPI on Windows using Dotnet, Native APIs & Registry keys.

Using Dotnet and Native APIs:

Directly creating and using a Graphics object

Graphics.DpiX Reference: https://learn.microsoft.com/en-us/dotnet/api/system.drawing.graphics.dpix

graphics = Graphics.FromHwnd(IntPtr.Zero)
DpiX = graphics.DpiX
graphics.Dispose()

DPI = DpiX 
DPI_SCALE_FACTOR = DPI / 96

Value Updation: After restarting the App

By creating and using a Graphics object from a Control object

Control Object Reference: https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.control

Graphics.DpiX Reference: https://learn.microsoft.com/en-us/dotnet/api/system.drawing.graphics.dpix

graphics = Form.CreateGraphics()
DpiX = graphics.DpiX
graphics.Dispose()

DPI = DpiX
DPI_SCALE_FACTOR = DPI / 96

Value Updation: After restarting the App

Using DeviceDpi from a Control object

Control Object Reference: https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.control

DeviceDpi Reference: https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.control.devicedpi

DPI = Form.DeviceDpi 
DPI_SCALE_FACTOR = DPI / 96

Value Updation: After restarting the App

Using GetDeviceCaps

Graphics Reference: https://learn.microsoft.com/en-us/dotnet/api/system.drawing.graphics

GetDeviceCaps Reference: https://webcache.googleusercontent.com/search?q=cache:https%3A%2F%2Fwww.pinvoke.net%2Fdefault.aspx%2Fgdi32.getdevicecaps

graphics = Graphics.FromHwnd(IntPtr.Zero)
hdc = graphics.GetHdc()

HORZRES = GetDeviceCaps(hdc.ToInt32(), 8)
DESKTOPHORZRES = GetDeviceCaps(hdc.ToInt32(), 118)

graphics.ReleaseHdc(hdc)
graphics.Dispose()

DPI = (DESKTOPHORZRES / HORZRES) * 96
DPI_SCALE_FACTOR = (DESKTOPHORZRES / HORZRES)

Value Updation: After restarting the App

Using GetSystemDpiForProcess

Reference: https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getsystemdpiforprocess

Value Updation: Not Tested yet

Using GetDpiForWindow

Reference: https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getdpiforwindow

NewDpi = GetDpiForWindow(Form.Handle())
NewDpiScaleFactor = NewDpi / 96

Value Updation: Not Tested yet

Using GetDpiForSystem

Reference: https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getdpiforsystem

Value Updation: Not Tested yet

Using DeviceDpiNew:

Reference: https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.dpichangedeventargs.devicedpinew

OnDpiChanged (System.Windows.Forms.DpiChangedEventArgs e)
NewDpi = e.DeviceDpiNew
NewDpiScaleFactor = NewDpi / 96

Using GetScaleFactorForMonitor

MonitorFromRect Reference: https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-monitorfromrect

GetScaleFactorForMonitor Reference: https://learn.microsoft.com/en-us/windows/win32/api/shellscalingapi/nf-shellscalingapi-getscalefactorformonitor

screen = Screen.PrimaryScreen
screen_rect = RECT(
    screen.Bounds.Left,
    screen.Bounds.Top,
    screen.Bounds.Right,
    screen.Bounds.Bottom,
)

hMonitor = MonitorFromRect(screen_rect, 2)
pScale = UINT()
GetScaleFactorForMonitor(hMonitor, &pScale)

DPI_SCALE = pScale / 100

Value Updation: Instant

NOTE:

It should be noted that some of these APIs report the correct values only when the app is running in various DPI aware modes only. Using them in non DPI aware mode apps will result in getting incorrect values.

Using Registry Keys:

LogPixels:

The values of the key correspond to the DPI settings of the system:

HKEY_CURRENT_USER\Control Panel\Desktop\LogPixels

Value Updation: Not sure as it is not present on the latest windows versions

AppliedDpi:

The value of the key changes according to the system DPI settings:

HKEY_CURRENT_USER\Control Panel\Desktop\WindowMetrics\AppliedDpi

Value Updation: After signing out and resigning in

FontDpi:

The value of these keys changes according to the system DPI settings:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\FontDPI
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\FontDPI

Value Updation: After signing out and resigning in

DpiValue:

The value of the key changes according to the system DPI settings:

HKEY_CURRENT_USER\Control Panel\Desktop\PerMonitorSettings\\*UniqueString*\\DpiValue

Value Updation: Instant

NOTE:

It should be noted that these registry keys are not public facing APIs. As such, they can be removed or modified by Windows, without any prior warning or notice. Hence, it is not recommended to use these registry keys.