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SystemParametersInfo(Spi_SetFontSmoothing, Cardinal(True), Nil, 0);
  repaint;                    

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unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    CheckBox1: TCheckBox;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure CheckBox1Click(Sender: TObject);
  private
    { Private-Deklarationen }
    smooth_active: boolean;
  public
    { Public-Deklarationen }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  SystemParametersInfo(SPI_GETFONTSMOOTHING, 1, @smooth_active, 0);
  checkbox1.Checked := smooth_active;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  SystemParametersInfo(SPI_SETFONTSMOOTHING, cardinal(smooth_active), nil, 0);
end;

procedure TForm1.CheckBox1Click(Sender: TObject);
var
  b : boolean;
begin
  b :=checkbox1.checked;
  SystemParametersInfo(SPI_SETFONTSMOOTHING, cardinal(b), 0, 0);
  repaint;
end;

end.