Tip 204: Changing the Screen Resolution at Run Time in Visual Basic 4.0

February 28, 1996

Abstract
Because Microsoft Windows 95 users may have different screen resolution
settings, you may need to set the screen resolution to a specific setting
while your Microsoft® Visual Basic® version 4.0 application is running.
This article explains how to change your screen resolution from within
Visual Basic.

Setting the Screen Resolution
Under the Microsoft® Windows® 95 operating system, you can set your screen
resolution by running the Display applet in Control Panel. In a Microsoft
Visual Basic® version 4.0 application, you can use the Windows application
programming interface (API) EnumDisplaySettings and ChangeDisplaySettings
functions to change the screen resolution while your program is running.

The EnumDisplaySettings function allows you to retrieve information about
your display's graphics modes. This information is then stored in a DEVMODE
structure.

After you have interrogated the computer system with the
EnumDisplaySettings function, you use the ChangeDisplaySettings function
to tell the operating system to use a different screen resolution.

The ChangeDisplaySettings function lets you set the screen resolution to
a different graphics mode. The DEVMODE structure holds the graphics mode
information to which you want to change.

In the example program below, you first retrieve the current screen
resolution information by calling the EnumDisplaySettings function. The
DEVMODE structure contains the graphics modes information for the display
type. Next, you modify the dmPelsWidth and dmPelsHeight fields in the
DEVMODE structure to reflect the new screen resolution you want to set.
Finally, you call the ChangeDisplaySettings function to tell the operating
system to set the new screen resolution as the default resolution.

Example Program
This program shows how to set the screen resolution from within a Visual
Basic application.

 1. Create a new project in Visual Basic. Form1 is created by default.
 2. Add the following code to the General Declarations section of Form1
    (note that each Declare statement must be typed as a single line of
    code):

Option Explicit
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_PELSWIDTH = &H80000
Const DM_PELSHEIGHT = &H100000

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
Dim DevM As DEVMODE

 3. Add a Command Button control to Form1. Command1 is created by default.
 4. Add the following code to the Click event for Command1:

Private Sub Command1_Click()
    Dim a As Boolean
    Dim i&
    i = 0
    Do
        a = EnumDisplaySettings(0&, i&, DevM)
        i = i + 1
    Loop Until (a = False)
End Sub

 5. Add a second Command Button control to Form1. Command2 is created
    by default.
 6. Add the following code to the Click event for Command2:

Private Sub Command2_Click()
    Dim b&
    DevM.dmFields = DM_PELSWIDTH Or DM_PELSHEIGHT
    DevM.dmPelsWidth = 800
    DevM.dmPelsHeight = 600
    b = ChangeDisplaySettings(DevM, 0)
End Sub

Run the example program by pressing F5. Click the first Command Button
control. This retrieves all the graphics modes for your display. Next,
click the second Command Button control to change the display's screen
resolution to 800 x 600 graphics mode.

Additional References
"ChangeDisplaySettings QuickInfo Overview Group." (Library,
   Product Documentation, SDKs, Win32 SDK, Win32 Programmer's Reference,
   Reference, Functions, AnsiPrev to CheckDlgButton)
"EnumDisplaySettings QuickInfo Overview Group." (Library,
   Product Documentation, SDKs, Win32 SDK, Win32 Programmer's Reference,
   Reference, Functions, DragAcceptFiles to EnumMonitors)