Author: Tomas Rutkauskas

According to Microsoft you could use a progress bar with style set to PBS_MARQUEE 
if you don't know the final value. It will show a progress bar with only a gradient 
going from left to right. I find no other references to these constants except from 
MSDN. Anyone know how to use them in Delphi?

Answer:

It's defined in CommCtrl.h:

#if (_WIN32_WINNT >= 0x0501)
#define PBS_MARQUEE             0x08
#define PBM_SETMARQUEE          (WM_USER+10)
#endif      // _WIN32_WINNT >= 0x0501

In Delphi (untested):

1   { ... }
2   const
3     PBS_MARQUEE = $08;
4     PBM_SETMARQUEE = (WM_USER + 10);
5   
6   You set this style by subclassing the TProgressBar.CreateParams methods and setting 
7   PBS_MARQUEE:
8   
9   procedure TMyProgressBar.CreateParams(var Params: TCreateParams);
10  begin
11    inherited CreateParams(Params);
12    Params.Style := Params.Style or PBS_MARQUEE;
13  end;
14  
15  //You can now turn on the marquee:
16  
17  SendMessage(MyProgressBar1.Handle, PBS_SETMARQUEE, 1, 200);
18  
19  //and off:
20  
21  SendMessage(MyProgressBar1.Handle, PBS_SETMARQUEE, 0, 200);


The 200 is the number of milliseconds between animation updates.