Scrolling a Memo text using TTimer shows only the first 3 Lines

Question

what i am trying to do right now is to create a scroling credit text using the TMemo component and TTimer

 procedure TAboutBox.Timer1Timer(Sender: TObject);
 begin
 Memo1.ScrollBy(0,-1);
 end;

the Tmemo lines contain the text of the credit, something like :

Thankyou to :
Junifer lamda
Exemple user 2
Coder Monalisa
etc etc

Everything work as expected, i've set the timer.interval to 1ms , the text scroll smoothly but it displays only the 3 first lines then it displays a blank space, unless i click and drag manually using the mouse inside the memo, then it displays some lines then it disappears again when i release.

I tried with both TRichedit and TListBox but the problem persist. How could this be ?

Yes it is, on win32 TTimer uses a Windows timer, and interval is clipped to USER_TIMER_MINIMUM (0x0000000A) — az01, Jan 01 '12 at 15:52
Do you also consider alternative answers excluding the use of a TMemo/TRichEdit/TlistBox? — menjaraz, Jan 01 '12 at 17:26

score 4 · Answer 1 · edited Jan 01 '12 at 16:36

4

It seems to me that ScrollBy is not designed to do what you desire. What's more I don't think that TMemo is necessary either.

I'd probably do this with a label and move it on the timer event. Like this:

procedure TScrollingTextForm.FormCreate(Sender: TObject);
begin
  Label1.Caption :=
    'Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do '+
    'eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad '+
    'minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip '+
    'ex ea commodo consequat. Duis aute irure dolor in reprehenderit in '+
    'voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur '+
    'sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt '+
    'mollit anim id est laborum.';
  Label1.Top := ClientHeight;
end;

procedure TScrollingTextForm.Timer1Timer(Sender: TObject);
begin
  Label1.Top := Label1.Top - 1;
end;

I found that I needed to make the form double buffered (DoubleBuffered := True) to avoid flicker when scrolling.

edited Jan 01 '12 at 16:36

LaKraven

5,804
2
23
49

answered Jan 01 '12 at 15:01

David Heffernan

601,492
42
1,072
1,490

4

I think it would be slightly more elegant to custom draw the text in the form's `OnPaint` event. – Andreas Rejbrand Jan 01 '12 at 15:31
@andreas I think you are right but I was aiming for a very simple answer. Happy New Year! – David Heffernan Jan 01 '12 at 16:35
your solution works perfectly, but the TLabel is flashing when it is moving which make it less elegent. Tried to put the code in the form Onpaint event but still flashing. ? – Rafik Bari Jan 01 '12 at 16:54
Set DoubleBuffered property of the form to true – David Heffernan Jan 01 '12 at 16:55

Scrolling a Memo text using TTimer shows only the first 3 Lines

1 Answers1