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[Luke1]

Option Explicit
Const WM_DISPLAYCHANGE = &H7E
Const HWND_BROADCAST = &HFFFF&
 
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 BITSPIXEL = 12
 
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 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
Private Declare Function GetDeviceCaps Lib "gdi32" (ByVal hdc As Long, ByVal nIndex As Long) As Long
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Dim OldX As Long, OldY As Long, nDC As Long
Sub ChangeRes(X As Long, Y As Long, Bits As Long)
Dim DevM As DEVMODE, ScInfo As Long, erg As Long, an As VbMsgBoxResult
'Get the info into DevM
erg = EnumDisplaySettings(0&, 0&, DevM)
'This is what we're going to change
DevM.dmFields = DM_PELSWIDTH Or DM_PELSHEIGHT Or DM_BITSPERPEL
DevM.dmPelsWidth = X 'ScreenWidth
DevM.dmPelsHeight = Y 'ScreenHeight
DevM.dmBitsPerPel = Bits '(can be 8, 16, 24, 32 or even 4)
'Now change the display and check if possible
erg = ChangeDisplaySettings(DevM, CDS_TEST)
'Check if succesfull
Select Case erg&
 
Case DISP_CHANGE_SUCCESSFUL
erg = ChangeDisplaySettings(DevM, CDS_UPDATEREGISTRY)
ScInfo = Y * 2 ^ 16 + X
'Notify all the windows of the screen resolution change
SendMessage HWND_BROADCAST, WM_DISPLAYCHANGE, ByVal Bits, ByVal ScInfo
Case Else
MsgBox "Mode not supported", vbOKOnly + vbSystemModal, "Error"
End Select
 
End Sub
 
Private Sub Form_Load()
Dim nDC As Long
'retrieve the screen's resolution
OldX = Screen.Width / Screen.TwipsPerPixelX
OldY = Screen.Height / Screen.TwipsPerPixelY
'Create a device context, compatible with the screen
 
'Change the screen's resolution
ChangeRes 640, 480, GetDeviceCaps(Me.hdc, BITSPIXEL)
End Sub
 
Private Sub Form_Unload(Cancel As Integer)
'restore the screen resolution
ChangeRes OldX, OldY, GetDeviceCaps(nDC, BITSPIXEL)
'delete our device context
End Sub