unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    procedure FormPaint(Sender: TObject);
    procedure FormClick(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses GDIPOBJ,GDIPAPI;

var
  pc: PChar = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
  num: Integer;

procedure TForm1.FormPaint(Sender: TObject);
var
  g: TGPGraphics;
  b: TGPBrush;
  font: TGPFont;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  b := TGPSolidBrush.Create(aclGoldenrod);

  font := TGPFont.Create('Arial Black', 18, FontStyleRegular);
  
  {参数 2 为输出字符的个数, -1 表示全部输出}
  g.DrawString(pc, num, font, MakePoint(5.0, 5), b);

  b.Free;
  font.Free;
  g.Free;
end;

procedure TForm1.FormClick(Sender: TObject);
var
  i,n: Integer;
begin
  n := Length(pc);
  num := 0;
  for i:= 1 to n do
  begin
    num := i;
    Repaint;
    Sleep(100);
    Application.ProcessMessages;
  end;

  num := -1;
  for i:= 1 to Length(pc) do
  begin
    Inc(pc);
    Repaint;
    Sleep(100);
    Application.ProcessMessages;
  end;

  Dec(pc,n);
end;

end.

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 42
  ClientWidth = 501
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  Position = poDesktopCenter
  OnClick = FormClick
  OnPaint = FormPaint
  PixelsPerInch = 96
  TextHeight = 13
end