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  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." (MSDN Library, SDK Documentation, Platform SDK)

"EnumDisplaySettings QuickInfo Overview Group." (MSDN Library, SDK Documentation, Platform SDK)