Visual Basic Enumeration/Callback Routines
ChangeDisplaySettings: Change Display Resolution
     
Posted:   Friday September 17, 1999
Updated:   Monday December 26, 2011
     
Applies to:   VB4-32, VB5, VB6
Developed with:   VB5, Windows 98
OS restrictions:   None
Author:   Joe LeVasseur
     

Related:  

ChangeDisplaySettings: Change Display Resolution
EnumDisplaySettings: Enumerate Available Display Resolutions
EnumDisplayDevices: Enumerating System Display Devices

EnumDisplayMonitors: Enumerating System Monitor Info
     
 Prerequisites
None.

ChangeDisplaySettings: Change Display Resolution(10354 bytes)This routine, like the ListView method in EnumDisplaySettings: Enumerate Available Display Resolutions, uses Windows' EnumDisplaySettings API to retrieve all the available screen resolutions supported by the display. Here, the results are used to create a "QuickRes-style menu", replete with the option of displaying the users display settings dialog.

While changing form one screen resolution to another within the same screen depth poses no problems, changing to another display depth may produce undesirable results. Memorize the locations of the settings option on the display properties in case you find yourself fumbling in the dark, so to speak.

The display enum and resolution changing code contained here was authored by Joe LeVasseur.

 BAS Module Code
Place the following code into the general declarations area of a bas module:

Option Explicit
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' Copyright 1996-2011 VBnet/Randy Birch, All Rights Reserved.
' Some pages may also contain other copyrights by the author.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' Distribution: You can freely use this code in your own
'               applications, but you may not reproduce 
'               or publish this code on any web site,
'               online service, or distribute as source 
'               on any media without express permission.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Public Declare Function EnumDisplaySettings Lib "user32" _
    Alias "EnumDisplaySettingsA" _
   (ByVal lpszDeviceName As Long, _
    ByVal iModeNum As Long, _
    lpDevMode As Any) As Long
          
Public Declare Function GetDeviceCaps Lib "gdi32" _
   (ByVal hdc As Long, _
    ByVal nIndex As Long) As Long

Public Declare Function ChangeDisplaySettings Lib "user32" _
    Alias "ChangeDisplaySettingsA" _
   (lpDevMode As Any, _
    ByVal dwflags As Long) As Long
          
Public Declare Function SetMenuDefaultItem Lib "user32" _
   (ByVal hMenu As Long, _
    ByVal uItem As Long, _
    ByVal fByPos As Long) As Long
  
Public Declare Function GetMenu Lib "user32" _
   (ByVal hWnd As Long) As Long
   
Public Declare Function GetSubMenu Lib "user32" _
   (ByVal hMenu As Long, _
   ByVal nPos As Long) As Long
          
Public Const LOGPIXELSX As Long = 88
Public Const LOGPIXELSY As Long = 90
Public Const BITSPIXEL As Long = 12
Public Const HORZRES As Long = 8
Public Const VERTRES As Long = 10

Public Const CCDEVICENAME As Long = 32
Public Const CCFORMNAME As Long = 32

Public Const DM_GRAYSCALE As Long = &H1
Public Const DM_INTERLACED As Long = &H2

Public Const DM_BITSPERPEL As Long = &H40000
Public Const DM_PELSWIDTH As Long = &H80000
Public Const DM_PELSHEIGHT As Long = &H100000
Public Const DM_DISPLAYFLAGS As Long = &H200000

Public Const CDS_UPDATEREGISTRY As Long = &H1
Public Const CDS_TEST As Long = &H2
Public Const CDS_FULLSCREEN As Long = &H4
Public Const CDS_GLOBAL As Long = &H8
Public Const CDS_SET_PRIMARY As Long = &H10
Public Const CDS_NORESET As Long = &H10000000
Public Const CDS_SETRECT As Long = &H20000000
Public Const CDS_RESET As Long = &H40000000
Public Const CDS_FORCE As Long = &H80000000

'Return values for ChangeDisplaySettings
'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 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
 Form Code
To a new form, add a top-level menu item, and name it "mnuDisplayModes". Add a single submenu item under this, and name this menu item "mnuModes". Set its index to 0 to create the necessary menu array. Add a command button (Command1), along with the following code:

Option Explicit

'vars set in load
Dim currHRes As Long
Dim currVRes As Long
Dim currBPP As Long

'var set in mnuModes
Dim currMenuItem As Long

'array of valid resolutions & colour depths
Dim resArray() As Long
   
'const for the members of the array
'i.e. resArray(resWidth, Index) = 1024
'i.e. resArray(resHeight, Index) = 768
'i.e. resArray(resDepth, Index)= 16  'Bits per pixel
Const resWidth = 1
Const resHeight = 2
Const resDepth = 3


Private Sub Form_Load()

  'retrieves the current screen resolution for
  'later comparison against DEVMODE values in
  'CompareSettings.
   currHRes = GetDeviceCaps(hdc, HORZRES)
   currVRes = GetDeviceCaps(hdc, VERTRES)
   currBPP = GetDeviceCaps(hdc, BITSPIXEL)
   
   Dim maxItems As Long
   InitializeDisplayMenu maxItems
   FinalizeDisplayMenu maxItems
   
End Sub


Private Sub FinalizeDisplayMenu(maxItems As Long)

  'This adds a separator and a final menu item,
  'providing the ability to open the control panel
  'display settings page from the app.
   If maxItems > 0 Then
   
      Dim hMenu As Long
      Dim r As Long
     
     'add the separator
      maxItems = maxItems + 1
      Load mnuModes(maxItems)
      mnuModes(maxItems).Caption = "-"
      
     'add the final item
      maxItems = maxItems + 1
      Load mnuModes(maxItems)
      mnuModes(maxItems).Caption = "Show Display Settings"
      
     'finally, bold the newly-added menuitem
      hMenu = GetSubMenu(GetMenu(Me.hWnd), 0)
      Call SetMenuDefaultItem(hMenu, maxItems - 1, True)
   
   End If
        
End Sub


Private Sub InitializeDisplayMenu(maxItems As Long)

   Dim DM As DEVMODE
   Dim dMode As Long
   
  '36 should be enough to hold your settings.
  'It's trimmed back at the end of this routine.
   ReDim resArray(1 To 3, 0 To 35)
   
  'set the DEVMODE flags and structure size
   DM.dmFields = DM_PELSWIDTH Or DM_PELSHEIGHT Or DM_BITSPERPEL
   DM.dmSize = LenB(DM)
   
  'The first mode is 0
   dMode = 0
      
  'call the API to retrieve the values for the
  'specified dMode
   Do While EnumDisplaySettings(0&, dMode, DM) > 0
   
     'if the BitsPerPixel is greater than 4
     '(16 colours), then add the item to a menu
      If DM.dmBitsPerPel >= 4 Then
         Call MenuAdd(DM, resArray(), maxItems)
      End If
      
     'increment and call again. Continue until
     'EnumDisplaySettings returns 0 (no more settings)
      dMode = dMode + 1
   
   Loop
   
  'trim back the resArray to fit the number of actual entries.
   ReDim Preserve resArray(1 To 3, 0 To maxItems)
   
End Sub


Private Function CompareSettings(DM As DEVMODE) As Long
   
  'compares the current screen resolution with
  'the current DEVMODE values.   Returns TRUE if
  'the horizontal and vertical resolutions, and
  'the bits per pixel colour depth, are the same.
   CompareSettings = (DM.dmBitsPerPel = currBPP) And _
                      DM.dmPelsHeight = currVRes And _
                      DM.dmPelsWidth = currHRes
   
End Function


Private Sub MenuAdd(DM As DEVMODE, resArray() As Long, mnuCount As Long)
 
   Dim mType As String
   
  'used to determine when the colour depth has
  'changed, so we can add a separator to the menu.
   Static lastBitsPerPel As Long
   
  'select the appropriate text string based on
  'the colour depth
   Select Case DM.dmBitsPerPel
      Case 4:      mType = "16 Color"
      Case 8:      mType = "256 Color"
      Case 16:     mType = "High Color"
      Case 24, 32: mType = "True Color"
   End Select

  'if this is the first item, we can't load the menu
  'array item, and it will not require a separator.
   If mnuCount > 0 Then
   
     'load a new menu item to the array
      Load mnuModes(mnuCount)
   
     'determine if the colour depth has changed. If so,
     'make the caption a separator, and load a new item
     'to hold the item.
      If lastBitsPerPel <> DM.dmBitsPerPel Then
      
         mnuModes(mnuCount).Caption = "-"
         mnuCount = mnuCount + 1
         Load mnuModes(mnuCount)
      
      End If
   End If
   
  'create the menu caption
   mnuModes(mnuCount).Caption = DM.dmPelsWidth & "x" & _
                                DM.dmPelsHeight & "  [" & _
                                DM.dmBitsPerPel & " bit " & _
                                mType & "]"
   
  'see if this is the current resolution,
  'and if so, check the menu item
   mnuModes(mnuCount).Checked = CompareSettings(DM)
   If mnuModes(mnuCount).Checked Then currMenuItem = mnuCount
   
   resArray(resWidth, mnuCount) = DM.dmPelsWidth
   resArray(resHeight, mnuCount) = DM.dmPelsHeight
   resArray(resDepth, mnuCount) = DM.dmBitsPerPel
   
  'save the current DEVMODE value for depth
  'and increment the menu item count, ready for
  'the next call
   lastBitsPerPel = DM.dmBitsPerPel
   mnuCount = mnuCount + 1
   
End Sub


Private Sub Command1_Click()

   Dim maxItems As Long
   
   InitializeDisplayMenu maxItems
   Command1.Enabled = False
   
   FinalizeDisplayMenu maxItems
   
End Sub


Private Sub mnuModes_Click(Index As Integer)

   Dim DM As DEVMODE
   
   Select Case Index
   
      Case mnuModes.Count
      
        'show the display control panel
         Call Shell("rundll32.exe shell32.dll,Control_RunDLL desk.cpl,,3", 1)
      
      Case Else
        
        'change the current resolution, no prompting
        'BE CAREFUL .. you could set your system to a
        'setting which renders the display difficult to read.
        
         With DM
         
            .dmPelsWidth = resArray(resWidth, Index)
            .dmPelsHeight = resArray(resHeight, Index)
            .dmBitsPerPel = resArray(resDepth, Index)
            .dmFields = DM_PELSWIDTH Or DM_PELSHEIGHT Or DM_BITSPERPEL
            .dmSize = LenB(DM)
         End With
         
         If ChangeDisplaySettings(DM, CDS_FORCE) <> 0 Then
         
             MsgBox "Error! Perhaps your hardware is not up to the task?"
             
         End If
         
        'indicate the current menu selection
         mnuModes(currMenuItem).Checked = False
         mnuModes(Index).Checked = True
         currMenuItem = Index
   
   End Select

End Sub
 Comments
On running, the menu should contain all your available settings, similar to those displayed in the ListView example. The current resolution will be checked.

Selecting another resolution or colour depth will cause the display to change without prompting. Be careful.


 
 

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