An easy pulsing effect

Problem/Question/Abstract:

How can I create a pulsing effect on a color in my program easily?

Answer:

It is easy because you only have to set a TDateTime variable at the beginning of your program, and then you are able to use pulsing colors like in QBASIC the color codes after 16. But it's finer.
So I show a program code. On Form1 there is a Timer1. Its interval is 50. Then the code should look like:

unit uPulse;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls;
type
TForm1 = class(TForm)
Timer1: TTimer;
procedure FormCreate(Sender: TObject);
procedure Timer1Timer(Sender: TObject);
{the .interval should be about 50, if it's high,
the framerate will be low}
private
{ Private declarations }
public
{ Public declarations }
end;

TFadingMode = (fmFlash, fmPulse); {Two types of the effect.}

var
Form1: TForm1;
Starting_Time: TDateTime;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
Starting_Time := Now;
end;

function TimeElapsed(Since: TDateTime): integer;
var
h, m, s, ms: Word;
begin
DecodeTime(Now - Since, h, m, s, ms);
Result := m * 60000 + s * 1000 + ms;
{
It may be: Result:=h*3600000+m*60000+s*1000+ms;
But not necessary.
}
end;

procedure TForm1.Timer1Timer(Sender: TObject);
const
PulsingRate = 500;
FadingMode = fmPulse;
{Modify these to get different results}
var
f: Byte; {the formula}
begin
case FadingMode of
{fades from color1 to color2 then turns back to color1}
fmFlash: f := 255 * (TimeElapsed(Starting_Time) mod PulsingRate) div PulsingRate;
{fades from color1 to color2 then fades back to color1}
fmPulse: f := 255 * Abs(TimeElapsed(Starting_Time) mod PulsingRate * 2 -
PulsingRate) div PulsingRate;
end;
{Then set the color with the RGB function}
Canvas.Brush.Color := RGB(f, 0, 0);
{
currently modifying RED, but you can get other colors like:
RGB(f,0,0) -     black->red
RGB(255-f,0,0) - red->black
RGB(0,f,0) -     black->green
RGB(50,150,f) -  green->blue
RGB(f,f,0) -     yellow->black
RGB(f,f,f) -     white->black
}
{then do the job... paint something etc.}
Canvas.Ellipse(50, 50, 150, 150);
end;

end.

It's good because you can refresh the screen anytimes, the result depends only on the time elapsed. You don't have to declare a lot of variables.
And you can use the formula everywhere where is a color used. Just refresh it often!