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Frequently Asked Questions

Changing the display mode settings in code.

Question:

How do I change the display mode settings in code?

Answer:

You can use the Windows API function EnumDisplaySettings() 

to get a list of valid mode settings, and use the Windows 

API function ChangeDisplaySettings() to actually change the 

display setting. Note that many drivers will not perform the 

reset without rebooting the computer, even though they are 

capable of doing so.



Example:



unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls, Spin;



type

  PdmArray = ^TDmArray;

  TDmArray = array[0..0] of TDeviceMode;



type

  TForm1 = class(TForm)

    Memo1: TMemo;

    SpinEdit1: TSpinEdit;

    Button1: TButton;

    procedure FormCreate(Sender: TObject);

    procedure FormDestroy(Sender: TObject);

    procedure Button1Click(Sender: TObject);

  private

    lpDmArray : PDmArray;

    NumModes : integer;

    { Private declarations }

  public

    { Public declarations }

  end;



var

  Form1: TForm1;



implementation



{$R *.DFM}



procedure TForm1.FormCreate(Sender: TObject);

var

  i : integer;  // auto-initialized to zero

  MoreModes : bool;

  dm : TDeviceMode;



begin

  Memo1.Lines.Clear;

  MoreModes := True;



  while MoreModes do begin

    MoreModes :=

      EnumDisplaySettings(nil,

                          i,

                          dm);

    Memo1.Lines.Add('Mode ' +

      IntToStr(i) + ': ' +

      IntToStr(dm.dmBitsPerPel) + ' Bits Per Pixel ' +

      IntToStr(dm.dmPelsWidth) + ' x ' +

      IntToStr(dm.dmPelsHeight));

    Inc(i);

  end;



  NumModes := i;

  SpinEdit1.MinValue := 0;

  SpinEdit1.MaxValue := NumModes;



  GetMem(lpDmArray, sizeof(TDeviceMode) * NumModes);

  FillChar(lpDmArray^, sizeof(TDeviceMode) * NumModes, #0);



{$IFOPT R+}

  {$DEFINE CKRANGE}

  {$R-}

{$ENDIF}

  for i := 0 to (NumModes - 1) do

    EnumDisplaySettings(nil,

                        i,

                        lpDmArray[i]);

{$IFDEF CKRANGE}

  {$UNDEF CKRANGE}

  {$R+}

{$ENDIF}

end;



procedure TForm1.Button1Click(Sender: TObject);

var

  ReturnVal : LongInt;

begin

{$IFOPT R+}

  {$DEFINE CKRANGE}

  {$R-}

{$ENDIF}

  ReturnVal := ChangeDisplaySettings(lpDmArray[SpinEdit1.Value],

                                     CDS_UPDATEREGISTRY);

{$IFDEF CKRANGE}

  {$UNDEF CKRANGE}

  {$R+}

{$ENDIF}

  with Memo1.Lines do begin

    case ReturnVal of

      DISP_CHANGE_SUCCESSFUL: Add('DISP_CHANGE_SUCCESSFUL');

      DISP_CHANGE_RESTART   : Add('DISP_CHANGE_RESTART');

      DISP_CHANGE_BADFLAGS  : Add('DISP_CHANGE_BADFLAGS');

      DISP_CHANGE_FAILED    : Add('DISP_CHANGE_FAILED');

      DISP_CHANGE_BADMODE   : Add('DISP_CHANGE_BADMODE');

      DISP_CHANGE_NOTUPDATED: Add('DISP_CHANGE_NOTUPDATED');

    end;

  end;

end;



procedure TForm1.FormDestroy(Sender: TObject);

begin

  FreeMem(lpDmArray, sizeof(TDeviceMode) * NumModes);

end;



end.

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