unit AniThread;

interface 

uses 
  Classes, Windows, Controls, Graphics; 

type 
  TAnimationThread = class(TThread) 
  private 
    { private declarations } 
    FWnd: HWND; 
    FPaintRect: TRect; 
    FbkColor, FfgColor: TColor; 
    FInterval: integer; 
  protected 
    procedure Execute; override; 
  public 
    constructor Create(paintsurface : TWinControl; {Control to paint on } 
      paintrect : TRect;          { area for animation bar }
      bkColor, barcolor : TColor; { colors to use }
      interval : integer);        { wait in msecs between paints}
  end; 

implementation 

constructor TAnimationThread.Create(paintsurface : TWinControl; 
  paintrect : TRect; bkColor, barcolor : TColor; interval : integer); 
begin 
  inherited Create(True); 
  FWnd := paintsurface.Handle; 
  FPaintRect := paintrect; 
  FbkColor := bkColor; 
  FfgColor := barColor; 
  FInterval := interval; 
  FreeOnterminate := True; 
  Resume; 
end; { TAnimationThread.Create } 

procedure TAnimationThread.Execute; 
var 
  image : TBitmap; 
  DC : HDC; 
  left, right : integer; 
  increment : integer; 
  imagerect : TRect; 
  state : (incRight, incLeft, decLeft, decRight); 
begin 
  Image := TBitmap.Create; 
  try 
    with Image do  
    begin 
      Width := FPaintRect.Right - FPaintRect.Left; 
      Height := FPaintRect.Bottom - FPaintRect.Top; 
      imagerect := Rect(0, 0, Width, Height); 
    end; { with } 
    left := 0; 
    right := 0; 
    increment := imagerect.right div 50; 
    state := Low(State); 
    while not Terminated do  
    begin 
      with Image.Canvas do  
      begin 
        Brush.Color := FbkColor; 
        FillRect(imagerect); 
        case state of 
          incRight:  
          begin 
            Inc(right, increment); 
            if right > imagerect.right then  
            begin 
              right := imagerect.right; 
              Inc(state); 
            end; { if } 
          end; { case incRight } 
          incLeft:  
          begin 
            Inc(left, increment); 
            if left >= right then  
            begin 
              left := right; 
              Inc(state); 
            end; { if } 
          end; { case incLeft } 
          decLeft:  
          begin 
            Dec(left, increment); 
            if left <= 0 then  
            begin 
              left := 0; 
              Inc(state); 
            end; { if } 
          end; { case decLeft } 
          decRight:  
          begin 
            Dec(right, increment); 
            if right <= 0 then  
            begin 
              right := 0; 
              state := incRight; 
            end; { if } 
          end; { case decLeft } 
        end; { case } 
        Brush.Color := FfgColor; 
        FillRect(Rect(left, imagerect.top, right, imagerect.bottom)); 
      end; { with } 
      DC := GetDC(FWnd); 
      if DC <> 0 then 
        try 
          BitBlt(DC, 
            FPaintRect.Left, 
            FPaintRect.Top, 
            imagerect.right, 
            imagerect.bottom, 
            Image.Canvas.handle, 
            0, 0, 
            SRCCOPY); 
        finally 
          ReleaseDC(FWnd, DC); 
        end; 
      Sleep(FInterval); 
    end; { while } 
  finally 
    Image.Free; 
  end; 
  InvalidateRect(FWnd, nil, True); 
end; { TAnimationThread.Execute } 

end. 

//============================ HOW to USE IT ============================
{
 Usage: 
 Place a TPanel on a form, size it as appropriate.Create an instance of the 
 TanimationThread call like this: procedure TForm1.Button1Click(Sender : TObject); } 
var 
  ani : TAnimationThread; 
  r : TRect; 
begin
  r := Panel1.ClientRect;
  InflateRect(r, - Panel1.BevelWidth, - Panel1.BevelWidth);
  ani := TAnimationThread.Create(Panel1, r, Panel1.color, clBlue, 25);
  Button1.Enabled := False; 
  Application.ProcessMessages; 
  Sleep(30000);  // replace with query.Open or such 
  Button1.Enabled := True; 
  ani.Terminate; 
  ShowMessage('Done'); 
end.