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'System & API - How to change System Resolution
Option Explicit
 
'The program will prompt to you if the computer must be restarted to apply changes.
Public Const CCDEVICENAME = 32
Public Const CCFORMNAME = 32
Public Const DISP_CHANGE_SUCCESSFUL = 0
Public Const DISP_CHANGE_RESTART = 1
Public Const DISP_CHANGE_FAILED = -1
Public Const DISP_CHANGE_BADMODE = -2
Public Const DISP_CHANGE_NOTUPDATED = -3
Public Const DISP_CHANGE_BADFLAGS = -4
Public Const DISP_CHANGE_BADPARAM = -5
Public Const CDS_UPDATEREGISTRY = &H1
Public Const CDS_TEST = &H2
Public Const DM_BITSPERPEL = &H40000
Public Const DM_PELSWIDTH = &H80000
Public Const DM_PELSHEIGHT = &H100000
Public 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
Declare Function EnumDisplaySettings Lib "user32" Alias "EnumDisplaySettingsA" _
    (ByVal lpszDeviceName As Long, ByVal iModeNum As Long, lpDevMode As Any) As Boolean
Declare Function ChangeDisplaySettings Lib "user32" Alias "ChangeDisplaySettingsA" _
    (lpDevMode As Any, ByVal dwFlags As Long) As Long
 
Private Sub Form_Load()
    'Replace '800,600' with the resolution you want to switch to.
    'You can change the color pallete to 32 - Bit by changing the '16' below with '32'
    ChangeScreenSettings 800, 600, 16 - Bit
End Sub
 
Public Sub ChangeScreenSettings(lWidth As Integer, lHeight As Integer, lColors As Integer)
    Dim tDevMode As DEVMODE, lTemp As Long, lIndex As Long
    lIndex = 0
    Do
        lTemp = EnumDisplaySettings(0&, lIndex, tDevMode)
        If lTemp = 0 Then Exit Do
        lIndex = lIndex + 1
        With tDevMode
            If .dmPelsWidth = lWidth And .dmPelsHeight = lHeight And .dmBitsPerPel = lColors Then
                lTemp = ChangeDisplaySettings(tDevMode, CDS_UPDATEREGISTRY)
                Exit Do
            End If
        End With
    Loop
    Select Case lTemp
    Case DISP_CHANGE_SUCCESSFUL
        MsgBox "The display settings changed successfully", vbInformation
    Case DISP_CHANGE_RESTART
        MsgBox "The computer must be restarted in order for the graphics mode to work", vbQuestion
    Case DISP_CHANGE_FAILED
        MsgBox "The display driver failed the specified graphics mode", vbCritical
    Case DISP_CHANGE_BADMODE
        MsgBox "The graphics mode is not supported", vbCritical
    Case DISP_CHANGE_NOTUPDATED
        MsgBox "Unable to write settings to the registry", vbCritical
    Case DISP_CHANGE_BADFLAGS
        MsgBox "You Passed invalid data", vbCritical
    End Select
End Sub