procedure TForm1.Timer1Timer(Sender: TObject);
 var i, b, c, wind, r: integer;

begin
randomize;
bitmap.Canvas.Pen.Color := clwhite;
bitmap.Canvas.Brush.Color := clblack;
bitmap.Canvas.Rectangle(0, 0, form1.Width, form1.Height);
bitmap.Canvas.Brush.Color := clwhite;
wind := - (((form1.Width + form1.Left) div 2 - mouse.CursorPos.X) div 60);
for i := 1 to 2000 do begin
  if (y[i] > Form1.Height) then begin
    r := random(100);
    if (r mod 3 = 0) then begin
    x[i] := - random(500);
    y[i] := random(Form1.height) - random(200);
  v[i] := random(3) + 3;
    end else if (r mod 3 = 1) then begin
    x[i] := Form1.Width + random(500);
    y[i] := random(Form1.height) - random(200);
  v[i] := random(3) + 3;
    end else begin
    y[i] := -random(100);
    x[i] := random(Form1.Width) + random(200) - 100;
  v[i] := random(3) + 3;
    end;
  end else begin
    y[i] := y[i] + v[i];
    x[i] := x[i] + wind;
  end;
  bitmap.Canvas.Ellipse(x[i],y[i],x[i]+4,y[i]+4);
end;
  Form1.Canvas.Draw(0, 0, bitmap);
end;

procedure TForm1.FormCreate(Sender: TObject);
var i : integer;
begin
  form1.Height :=  form1.Height;
  bitmap := Tbitmap.create;
  bitmap.Height := form1.Height;
  bitmap.Width := form1.Width;
  for i := 1 to 2000 do begin
  y[i] := random(Form1.height + 500) - 250;
  x[i] := random(Form1.width + 500) - 250;
  v[i] := random(3) + 3;
  end;
end;