Private Declare Function EnumDisplaySettings Lib "user32" _
        Alias "EnumDisplaySettingsA" (ByVal lpszDeviceName _
        As Long, ByVal iModeNum As Long, lpDevMode As Any) _
        As Boolean
 
Private Declare Function ChangeDisplaySettings Lib "user32" _
        Alias "ChangeDisplaySettingsA" (lpDevMode As Any, _
        ByVal dwFlags As Long) As Long
 
Const CCDEVICENAME = 32
Const CCFORMNAME = 32
Const DM_BITSPERPEL = &H40000
Const DM_PELSWIDTH = &H80000
Const DM_PELSHEIGHT = &H100000
Const CDS_UPDATEREGISTRY = &H1
Const CDS_TEST = &H4
Const DISP_CHANGE_SUCCESSFUL = 0
Const DISP_CHANGE_RESTART = 1
Const ENUM_CURRENT_SETTINGS = &HFFFF - 1
 
Private Type DEVMODE
  dmDeviceName As String * CCDEVICENAME
  dmSpecVersion As Integer
  dmDriverVersion As Integer
  dmSize As Integer
  dmDriverExtra As Integer
  dmFields As Long
  dmOrientation As Integer
  dmPaperSize As Integer
  dmPaperLength As Integer
  dmPaperWidth As Integer
  dmScale As Integer
  dmCopies As Integer
  dmDefaultSource As Integer
  dmPrintQuality As Integer
  dmColor As Integer
  dmDuplex As Integer
  dmYResolution As Integer
  dmTTOption As Integer
  dmCollate As Integer
  dmFormName As String * CCFORMNAME
  dmUnusedPadding As Integer
  dmBitsPerPel As Integer
  dmPelsWidth As Long
  dmPelsHeight As Long
  dmDisplayFlags As Long
  dmDisplayFrequency As Long
End Type
 
Private Sub Option1_Click(Index As Integer)
  Dim x&, y&
    Select Case Index
      Case 0: x = 800: y = 600
      Case 1: x = 1024: y = 768
      Case 2: x = 1152: y = 864
    End Select
    Call SetScreen(x, y)
End Sub
 
Private Sub SetScreen(ByVal x&, ByVal y&)
  Dim Result&
  Dim Dev As DEVMODE
 
    Call EnumDisplaySettings(0&, ENUM_CURRENT_SETTINGS, Dev)
    Dev.dmDisplayFrequency = 90
    Dev.dmFields = DM_PELSWIDTH Or DM_PELSHEIGHT
    Dev.dmPelsWidth = x
    Dev.dmPelsHeight = y
 
    Result = ChangeDisplaySettings(Dev, CDS_TEST)
    ChangeDisplay
End Sub