System.Drawing.Graphics.DpiX always return 96

Question

I have vb.net winform app that has AutoScaleMode = dpi AutoScale = false AutoSize = true

I\'ve signed off after changing DPI setting. I also tried restarting the machine

Answer 1

Unfortunately, the way windows handles DPI scaling is all over the place:

Using g As Graphics = form.CreateGraphics()
Dim dpiX As Single = g.DpiX

This code will only work if user has "Use Windows XP Style DPI Scaling" selected when setting custom DPI. Don't know if that option is even available in the new versions of Windows (8.x and 10) or if they've taken it out.

Your best bet would be to just read the registry:

    Dim regUseDpiScaling As Integer
    Try 'Use Try / Catch since the reg value may not exist if user using 96 DPI.
        regUseDpiScaling = CInt(My.Computer.Registry.GetValue("HKEY_CURRENT_USER\Software\Microsoft\Windows\DWM", "UseDpiScaling", Nothing)) ' if this returns 1, it means users is using modern DPI scaling.
    Catch ex As Exception
        regUseDpiScaling = 0 ' 0 means no DPI scaling or XP DPI scaling
    End Try
    If Not (regUseDpiScaling = 0) Then
        boolUsesModernDPIScaling = True 'Means you haven't clicked "Use Windows XP Style DPI Scaling" while setting DPI in your system.
    Else
        boolUsesModernDPIScaling = False
        MsgBox("2")
    End If

    Dim regAppliedDPI As Integer
    Try
        regAppliedDPI = CInt(My.Computer.Registry.GetValue("HKEY_CURRENT_USER\Control Panel\Desktop\WindowMetrics", "AppliedDPI", Nothing))
    Catch ex As Exception
        regAppliedDPI = 96
    End Try
    DPIratioX = regAppliedDPI / 96 
    DPIratioY = regAppliedDPI / 96

I found that having XP DPI scaling can result in different behavior, so it's good to have the program detect if it's being used.