PascalABC — Режим передвижения кисти без оставления следа?

uses graphabc,crt,events;

var x,y:integer;
    c:char;
    drawmode: string;

const WH = 600;
      WW = 600;
      color_px = clBlack;

procedure draw_px(col:integer);
begin
  SetPenColor(col);
  SetBrushColor(col);
  rectangle(x,y,x+10,y+10)
end;



procedure kDown(key: integer); { ????????? ????????? ??????? ?????? }
begin
  if drawmode = 'no' then draw_px(clWhite);   //ðåæèì ëàñòèêà
  if key=VK_Left then x:=x-10; { ????? }
  if key=VK_Right then x:=x+10; { ?????? }
  if key=VK_Up then y:=y-10; { ????? }
  if key=VK_Down then y:=y+10; { ???? }
  if key=VK_Escape then CloseWindow; { ??????? ???? }
  if key=VK_Space then
     begin
      if drawmode = 'yes' then
        drawmode:='no'
      else
        if drawmode = 'no' then
           drawmode:='yes';
    end;
  if key=VK_Tab then
    begin
      if PenStyle = psClear then
        SetPenStyle(psSolid)
      else
        if PenStyle = psSolid then
          SetPenStyle(psClear);
    end;

  SetWindowCaption('x='+IntToStr(x)+' y='+IntToStr(y) + ' flag=' + drawmode );
  draw_px(clBlack);
end;


begin
  setWindowSize(WH,WW);
  x := WW div 2;
  y := WH div 2;
  drawmode:= 'yes';
  OnKeyDown:=kDown;

end.