screen resolution

[basti42]

hello!
i could i do this?

when i load form1 it will check the screen resolution
if it is not 800x600 it will convert to 800x600 pixels
and when i close the form1 it will go back to previous resolution.

pls. help.

[jmcilhinney]

I'm fairly certain that you have to use the Windows API to set the screen resolution, although I can't recall which function. I would ask though, why exactly you want to change the resolution. This question has been asked many times and more often than not it is misguided. Changing the user's screen resolution is something that should very rarely be done.

[RobDog888]

Right, users hate it when a program changes the screen resolution.

If you still want to do it use the ChangeDisplaySettings API.

[basti42]

i'm writing a POS that's why i want to display it 800x600 pixels
it is easy for the cashier to see the value (money)

and in 800x600 it is ease in the eyes.

can you give example about the API how to change the resolution?

i found this code here in forums but i don't know how to convert in C#
if anyone can convert this, this is to solve my problem.

Option Explicit

Const WM_DISPLAYCHANGE = &H7E
Const HWND_BROADCAST = &HFFFF&
Const EWX_LOGOFF = 0
Const EWX_SHUTDOWN = 1
Const EWX_REBOOT = 2
Const EWX_FORCE = 4
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 ExitWindowsEx Lib "user32" (ByVal uFlags As Long, ByVal dwReserved As Long) As Long
Private Declare Function GetDeviceCaps Lib "gdi32" (ByVal hdc As Long, ByVal nIndex As Long) As Long
Private Declare Function CreateDC Lib "gdi32" Alias "CreateDCA" (ByVal lpDriverName As String, _
ByVal lpDeviceName As String, ByVal lpOutput As String, ByVal lpInitData As Any) As Long
Private Declare Function DeleteDC Lib "gdi32" (ByVal hdc 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

Public OldX As Long
Public OldY As Long
Public nDC As Long

Private Sub ChangeResolution(x As Long, Y As Long, Bits As Long)
    Dim DevM As DEVMODE, ScInfo As Long, erg As Long, an As VbMsgBoxResult
    erg = EnumDisplaySettings(0&, 0&, DevM)
    DevM.dmFields = DM_PELSWIDTH Or DM_PELSHEIGHT Or DM_BITSPERPEL
    DevM.dmPelsWidth = x
    DevM.dmPelsHeight = Y
    DevM.dmBitsPerPel = Bits
    erg = ChangeDisplaySettings(DevM, CDS_TEST)
    Select Case erg&
        Case DISP_CHANGE_RESTART
            an = MsgBox("You need to restart your computer for new settings to take effect.", vbYesNo + vbSystemModal, "Info")
            If an = vbYes Then
                erg& = ExitWindowsEx(EWX_REBOOT, 0&)
            End If
        Case DISP_CHANGE_SUCCESSFUL
            erg = ChangeDisplaySettings(DevM, CDS_UPDATEREGISTRY)
            ScInfo = Y * 2 ^ 16 + x
            SendMessage HWND_BROADCAST, WM_DISPLAYCHANGE, ByVal Bits, ByVal ScInfo
    End Select
End Sub

Public Sub ResizeDisplay(ByVal Enabled As Boolean, Optional ByVal x As Long, Optional ByVal Y As Long)
    If Enabled And Not IsMissing(x) And Not IsMissing(Y) Then
        If x And Y > 0 Then
            OldX = Screen.Width / Screen.TwipsPerPixelX
            OldY = Screen.Height / Screen.TwipsPerPixelY
            nDC = CreateDC("DISPLAY", vbNullString, vbNullString, ByVal 0&)
            ChangeResolution x, Y, GetDeviceCaps(nDC, BITSPIXEL)
        End If
    Else
        If OldX And OldY > 0 Then
            ChangeResolution OldX, OldY, GetDeviceCaps(nDC, BITSPIXEL)
            DeleteDC nDC
        End If
    End If
End Sub

[RobDog888]

Its VB 6 code so its manually convertable.

Heres the first part.

using System.Runtime.InteropServices;

public sealed class modMain
{
	private const int WM_DISPLAYCHANGE = 0X7E;
	private const int HWND_BROADCAST = 0XFFFFL;
	private const int EWX_LOGOFF = 0;
	private const int EWX_SHUTDOWN = 1;
	private const int EWX_REBOOT = 2;
	private const int EWX_FORCE = 4;
	private const int CCDEVICENAME = 32;
	private const int CCFORMNAME = 32;
	private const int DM_BITSPERPEL = 0X40000;
	private const int DM_PELSWIDTH = 0X80000;
	private const int DM_PELSHEIGHT = 0X100000;
	private const int CDS_UPDATEREGISTRY = 0X1;
	private const int CDS_TEST = 0X4;
	private const int DISP_CHANGE_SUCCESSFUL = 0;
	private const int DISP_CHANGE_RESTART = 1;
	private const int BITSPIXEL = 12;

	[StructLayout(LayoutKind.Sequential)]
	private struct DEVMODE
	{
	[MarshalAs(UnmanagedType.ByValTStr, SizeConst=CCHDEVICENAME)]
	public string dmDeviceName;
		public Int16 dmSpecVersion;
		public Int16 dmDriverVersion;
		public Int16 dmSize;
		public Int16 dmDriverExtra;
		public Int32 dmFields;
		public Int16 dmOrientation;
		public Int16 dmPaperSize;
		public Int16 dmPaperLength;
		public Int16 dmPaperWidth;
		public Int16 dmScale;
		public Int16 dmCopies;
		public Int16 dmDefaultSource;
		public Int16 dmPrintQuality;
		public Int16 dmColor;
		public Int16 dmDuplex;
		public Int16 dmYResolution;
		public Int16 dmTTOption;
		public Int16 dmCollate;
		public string * CCHFORMNAME dmFormName;
		public Int16 dmUnusedPadding;
		public Int16 dmBitsPerPel;
		public Int32 dmPelsWidth;
		public Int32 dmPelsHeight;
		public Int32 dmDisplayFlags;
		public Int32 dmDisplayFrequency;
	}

}

[RobDog888]

[System.Runtime.InteropServices.DllImport("user32", EntryPoint="EnumDisplaySettingsA", ExactSpelling=true, CharSet=System.Runtime.InteropServices.CharSet.Ansi, SetLastError=true)]
private static extern bool EnumDisplaySettings(long lpszDeviceName, long iModeNum, Any lpDevMode);

[System.Runtime.InteropServices.DllImport("user32", EntryPoint="ChangeDisplaySettingsA", ExactSpelling=true, CharSet=System.Runtime.InteropServices.CharSet.Ansi, SetLastError=true)]
private static extern long ChangeDisplaySettings(Any lpDevMode, long dwFlags);

[System.Runtime.InteropServices.DllImport("user32", EntryPoint="ExitWindowsEx", ExactSpelling=true, CharSet=System.Runtime.InteropServices.CharSet.Ansi, SetLastError=true)]
private static extern long ExitWindowsEx(long uFlags, long dwReserved);

[System.Runtime.InteropServices.DllImport("gdi32", EntryPoint="GetDeviceCaps", ExactSpelling=true, CharSet=System.Runtime.InteropServices.CharSet.Ansi, SetLastError=true)]
private static extern long GetDeviceCaps(long hdc, long nIndex);

[System.Runtime.InteropServices.DllImport("gdi32", EntryPoint="CreateDCA", ExactSpelling=true, CharSet=System.Runtime.InteropServices.CharSet.Ansi, SetLastError=true)]
private static extern long CreateDC(string lpDriverName, string lpDeviceName, string lpOutput, Any lpInitData);

[System.Runtime.InteropServices.DllImport("gdi32", EntryPoint="DeleteDC", ExactSpelling=true, CharSet=System.Runtime.InteropServices.CharSet.Ansi, SetLastError=true)]
private static extern long DeleteDC(long hdc);

[System.Runtime.InteropServices.DllImport("user32", EntryPoint="SendMessageA", ExactSpelling=true, CharSet=System.Runtime.InteropServices.CharSet.Ansi, SetLastError=true)]
private static extern long SendMessage(long hwnd, long wMsg, long wParam, Any lParam);

The rest should be easier to change to C# so let you give it a try.

[basti42]

i am not so advance in API so please guide me...

errors:
1. Any is not recognize so i change it ti "long"

2. public string * CCHFORMNAME dmFormName;
Error 2 Invalid token ';' in class, struct, or interface member declaration

what's next?

[Lord Orwell]

If it's a cash register, then why don't you manually set it to 800x600 and lock out users from changing it?

[basti42]

ok thank you for your efforts
nowadays nothing is impossible...
because i have mutiple forms with. the only 800x600pixels is the POS itself.
but i have solved my problem. if anyone want to change their resolution try this.

 [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
        struct DEVMODE
        {
            public const int DM_PELSWIDTH = 0x80000;
            public const int DM_PELSHEIGHT = 0x100000;   
            private const int CCHDEVICENAME = 32;
            private const int CCHFORMNAME = 32;

          [MarshalAs(UnmanagedType.ByValTStr, SizeConst=CCHDEVICENAME)]
            public string dmDeviceName;
            public short dmSpecVersion;
            public short dmDriverVersion;
            public short dmSize;
            public short dmDriverExtra;
            public int dmFields;

            public int dmPositionX;
            public int dmPositionY;
            public DMDO dmDisplayOrientation;
            public int dmDisplayFixedOutput;

            public short dmColor;
            public short dmDuplex;
            public short dmYResolution;
            public short dmTTOption;
            public short dmCollate;
          [MarshalAs(UnmanagedType.ByValTStr, SizeConst=CCHFORMNAME)]
            public string dmFormName;
            public short dmLogPixels;
            public int dmBitsPerPel;
            public int dmPelsWidth;
            public int dmPelsHeight;
            public int dmDisplayFlags;
            public int dmDisplayFrequency;
            public int dmICMMethod;
            public int dmICMIntent;
            public int dmMediaType;
            public int dmDitherType;
            public int dmReserved1;
            public int dmReserved2;
            public int dmPanningWidth;
        }
        //--------------------------------\
       
        [DllImport("user32.dll", CharSet=CharSet.Auto)]
        //static extern int ChangeDisplaySettings( DEVMODE lpDevMode,  int dwFlags);
       
        // should I use this line?
        static extern int ChangeDisplaySettings( [In] ref DEVMODE lpDevMode,  int dwFlags);

        void ChangeRes()
        {
            long RetVal=0;
           
            DEVMODE dm = new DEVMODE();
            dm.dmSize= (short)Marshal.SizeOf(typeof(DEVMODE));

            dm.dmPelsWidth = 800;
            dm.dmPelsHeight= 600;
            dm.dmFields = DEVMODE.DM_PELSWIDTH | DEVMODE.DM_PELSHEIGHT;
           
            RetVal = ChangeDisplaySettings(ref dm, 0);
        }