Changing the Screen Resolution

Imports System.Runtime.InteropServices

⋮

Private Declare Auto Function EnumDisplaySettings Lib "user32.dll" ( _
    <MarshalAs(UnmanagedType.LPTStr)> ByVal lpszDeviceName As String, _
    ByVal iModeNum As Int32, _
    ByRef lpDevMode As DEVMODE _
) As Boolean

Private Declare Auto Function ChangeDisplaySettings Lib "user32.dll" ( _
    ByRef lpDevMode As DEVMODE, _
    ByVal dwFlags As Int32 _
) As Int32

Private Const DM_BITSPERPEL As Int32 = &H40000
Private Const DM_PELSWIDTH As Int32 = &H80000
Private Const DM_PELSHEIGHT As Int32 = &H100000

Private Const DISP_CHANGE_SUCCESSFUL As Int32 = 0

<StructLayout(LayoutKind.Sequential)> _
Private Structure POINTL
    Public x As Int32
    Public y As Int32
End Structure

<StructLayout(LayoutKind.Explicit)> _
Private Structure DEVMODE_union1
    ' struct {
        <FieldOffset(0)> Public dmOrientation As Int16
        <FieldOffset(2)> Public dmPaperSize As Int16
        <FieldOffset(4)> Public dmPaperLength As Int16
        <FieldOffset(6)> Public dmPaperWidth As Int16
    ' }
    <FieldOffset(0)> Public dmPosition As POINTL
End Structure

<StructLayout(LayoutKind.Explicit)> _
Private Structure DEVMODE_union2
    <FieldOffset(0)> Public dmDisplayFlags As Int32
    <FieldOffset(0)> Public dmNup As Int32
End Structure

<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Auto)> _
Private Structure DEVMODE
    Private Const CCDEVICENAME As Int32 = 32
    Private Const CCFORMNAME As Int32 = 32

    <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=CCDEVICENAME)> _
    Public dmDeviceName As String
    Public dmSpecVersion As Int16
    Public dmDriverVersion As Int16
    Public dmSize As Int16
    Public dmDriverExtra As Int16
    Public dmFields As Int32
    Public u1 As DEVMODE_union1
    Public dmScale As Int16
    Public dmCopies As Int16
    Public dmDefaultSource As Int16
    Public dmPrintQuality As Int16
    Public dmColor As Int16
    Public dmDuplex As Int16
    Public dmYResolution As Int16
    Public dmTTOption As Int16
    Public dmCollate As Int16
    <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=CCFORMNAME)> _
    Public dmFormName As String
    Public dmUnusedPadding As Int16
    Public dmBitsPerPel As Int16
    Public dmPelsWidth As Int32
    Public dmPelsHeight As Int32
    Public u2 As DEVMODE_union2
    Public dmDisplayFrequency As Int32
    Public dmICMMethod As Int32
    Public dmICMIntent As Int32
    Public dmMediaType As Int32
    Public dmDitherType As Int32
    Public dmReserved1 As Int32
    Public dmReserved2 As Int32
    Public dmPanningWidth As Int32
    Public dmPanningHeight As Int32
End Structure

Public Function SetResolution( _
    ByVal Width As Int32, _
    ByVal Height As Int32, _
    ByVal BitsPerPixel As Int16 _
) As Boolean
    Dim dm As DEVMODE
    If Not EnumDisplaySettings(Nothing, 0, dm) Then
        Return False
    Else
        With dm
            .dmFields = _
                DM_PELSWIDTH Or DM_PELSHEIGHT Or DM_BITSPERPEL
            .dmPelsWidth = Width
            .dmPelsHeight = Height
            .dmBitsPerPel = BitsPerPixel
        End With
        Return (ChangeDisplaySettings(dm, 0) = DISP_CHANGE_SUCCESSFUL)
    End If
End Function

Debug.Assert(SetResolution(1024, 768, 32))