unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormPaint(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

var
  bit: TBITMAP;
  f: Boolean;
  x1,y1: Integer;
  cvs: TCanvas;

procedure TForm1.FormCreate(Sender: TObject);
var
  Rgn: HRGN;
begin
  bit := TBitmap.Create;
  bit.LoadFromFile('c:\temp\Test.bmp');
  ClientWidth := bit.Width;
  ClientHeight := bit.Height;

  cvs := TCanvas.Create;
  cvs.Handle := GetDC(Handle);

  Rgn := CreateEllipticRgn(30,30,140,140);
  SelectClipRgn(cvs.Handle, Rgn);

  DeleteObject(Rgn);
end;

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if PtVisible(cvs.Handle, X, Y) then
  begin
    f := True;
    x1 := X;
    y1 := Y;
  end;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if not f then Exit;
  OffsetClipRgn(cvs.Handle, X-x1, Y-Y1);
  Repaint;
  x1 := X;
  y1 := Y;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  f := False;
end;

procedure TForm1.FormPaint(Sender: TObject);
begin
  cvs.Draw(0,0,bit);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  bit.Free;
  cvs.Free;
end;

end.

object Form1: TForm1
  Left = 402
  Top = 230
  Caption = 'Form1'
  ClientHeight = 206
  ClientWidth = 339
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  Position = poDesigned
  OnCreate = FormCreate
  OnDestroy = FormDestroy
  OnMouseDown = FormMouseDown
  OnMouseMove = FormMouseMove
  OnMouseUp = FormMouseUp
  OnPaint = FormPaint
  PixelsPerInch = 96
  TextHeight = 13
end