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unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls, ComCtrls;

type
  TForm1 = class(TForm)
    TB1: TTrackBar;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    CheckBox1: TCheckBox;
    procedure FormCreate(Sender: TObject);
    procedure TB1Change(Sender: TObject);

  private
    { Private declarations }
  public
    { Public declarations }
  end;

const
  FILE_DEVICE_VIDEO = $23;
  METHOD_BUFFERED = 0;
  FILE_ANY_ACCESS = 0;

  IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS =
    FILE_DEVICE_VIDEO shl 16 or $127 shl 2 or
    METHOD_BUFFERED shl 14 or
    FILE_ANY_ACCESS;

  IOCTL_VIDEO_QUERY_DISPLAY_BRIGHTNESS =
  FILE_DEVICE_VIDEO Shl 16 Or $126 Shl 2 Or
    METHOD_BUFFERED Shl 14 Or
    FILE_ANY_ACCESS;

  IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS =
    FILE_DEVICE_VIDEO Shl 16 Or $125 Shl 2 Or
    METHOD_BUFFERED Shl 14 Or
    FILE_ANY_ACCESS;

  DISPLAYPOLICY_AC = 1;
  DISPLAYPOLICY_DC = 2;
  DISPLAYPOLICY_BOTH = 3;
  LCDDeviceFile = '\\.\LCD';

type
  TDisplayBrightness = packed record
    ucDisplayPolicy: Byte;
    ucACBrightness: Byte;
    ucDCBrightness: Byte;
  end;

var Form1: TForm1;
  g_displayPolicy: integer = 0;
  g_supportedLevels: byte;
  g_supportedLevelCount: DWORD = 0;

implementation

{$R *.dfm}

function GetLcdDevice(): integer;
var lcd: Thandle;
begin
  result:=0;
  lcd := CreateFile(LCDDeviceFile, FILE_ANY_ACCESS, 0, nil, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);
  //check handle:
  if lcd = INVALID_HANDLE_VALUE then
  begin
    ShowMessage('An error occurred opening the LCD device');
    exit;
  end
  else result:= lcd;
end;

function QuerySupportedLevels(): integer;
var lcd: HFILE;
begin
  result:=0;
  ZeroMemory(@g_supportedLevels, sizeof(g_supportedLevels));
  lcd:= GetLcdDevice();
  if DeviceIoControl(lcd, IOCTL_VIDEO_QUERY_SUPPORTED_BRIGHTNESS, nil, 0, @g_supportedLevels, 256, &g_supportedLevelCount, nil) then
    if g_supportedLevelCount= 0 then
      begin
      ShowMessage('Your video card or driver does not support brightness control.');
      result:= 0;
      end
    else
      result:= g_supportedLevelCount
  else
    ShowMessage('An error occurred querying supported brightness levels.');
end;


Function GetLCD_DCBrightnessLevel: Byte;
Var
    lcd: HFILE;
    DispBrightness: TDisplayBrightness;
    BufSize: DWORD;
Begin
    Result := 0;
    lcd:= GetLcdDevice();
    Try
        BufSize := SizeOf(DispBrightness);
        If Not DeviceIoControl(lcd, IOCTL_VIDEO_QUERY_DISPLAY_BRIGHTNESS, Nil, 0, @DispBrightness, BufSize, BufSize, Nil) Then
            Exit;
        Result := DispBrightness.ucDCBrightness;
    Finally
        CloseHandle(lcd);
    End;
End;

function SetBrightness(Value: integer): Boolean;
var bytesReturned: DWORD;
    lcd: Thandle;
    brightness: TDisplayBrightness;
begin
  result:= false;
  brightness.ucDisplayPolicy := g_displayPolicy;
  brightness.ucACBrightness := Value;
  brightness.ucDCBrightness := Value;

  lcd := GetLcdDevice();
  if lcd = INVALID_HANDLE_VALUE then
  begin
    ShowMessage('An error occurred opening the LCD device');
    exit;
  end else
    Result:=true;

  if DeviceIoControl(lcd, IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS, @brightness,
    sizeof(brightness), nil, 0, bytesReturned, nil) = false then
    ShowMessage('Error, DeviceIoControl returned False');
  CloseHandle(lcd);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  TB1Change(Self);
  Label2.Caption:= IntToStr(QuerySupportedLevels()-1);
end;

procedure TForm1.TB1Change(Sender: TObject);
begin
  CheckBox1.checked:= not SetBrightness(TB1.Position);
  Label1.Caption:= IntToStr(GetLCD_DCBrightnessLevel);
  TB1.SelStart:=0; TB1.SelEnd:= TB1.Position;
end;

end.