unit ClockWipe;
interface
uses
 Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, ExtCtrls, StdCtrls;
type
 TPkt = array[0..361] of TPoint;
type
 TForm1 = class(TForm)
  Image1: TImage;
  Image2: TImage;
  Button1: TButton;
  procedure FormPaint(Sender: TObject);
  procedure Button1Click(Sender: TObject);
 private
  procedure ClockWipe(re: TRect; Bmp: TBitmap);
  procedure SetPolygonRegion(Pkt: TPkt; PktCount: Integer; Bmp: TBitmap);
  function GetArcPoint(cPoint: TPoint; radius, winkel: Integer): TPoint;
 public
  { Public Declarations }
 end;
var
 Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
begin
 Canvas.Draw(0, 0, Image1.Picture.Bitmap);
 ClockWipe(Image2.Picture.Bitmap.Canvas.ClipRect, Image2.Picture.Bitmap);
end;
procedure TForm1.FormPaint(Sender: TObject);
begin
 Canvas.Draw(0, 0, Image1.Picture.Bitmap);
end;
procedure TForm1.ClockWipe(re: TRect; Bmp: TBitmap);
var
 radius, winkel, cv: Integer;
 cP: TPoint;
 Pkt: TPkt;
begin
 radius := Round(Sqrt(Sqr((re.right - re.left) div 2) + Sqr((re.bottom - re.top) div 2)));
 cP := Point((re.right - re.left) div 2, (re.bottom - re.top) div 2);
 Pkt[0] := cP;
 for winkel := 0 to 360 do
  Pkt[winkel + 1] := GetArcPoint(cP, radius, winkel + 90);
 for cv := 0 to 361 do
  if (cv - 1) / 20 = (cv - 1) div 20 then
  begin
  Sleep(50);
  SetPolygonRegion(Pkt, cv + 1, Image2.Picture.Bitmap);
  end;
end;
procedure TForm1.SetPolygonRegion(Pkt: TPkt; PktCount: Integer; Bmp: TBitmap);
var
 Region: HRGN;
begin
 Region := CreatePolygonRGN(Pkt, PktCount, WINDING);
 if Region <> 0 then
 begin
  SelectClipRgn(Canvas.handle, Region);
  Canvas.Draw(0, 0, Bmp);
  SelectClipRgn(Canvas.handle, 0);
  DeleteObject(Region);
 end;
end;
function TForm1.GetArcPoint(cPoint: TPoint; radius, winkel: Integer): TPoint;
begin
 result.x := Round(cPoint.x + radius * Cos(winkel * 2 * pi / 360));
 result.y := Round(cPoint.y - radius * Sin(winkel * 2 * pi / 360));
end;
end.