Board index » delphi » Problem with flicker when resizing but not when moving?

2004-06-13 05:14:19 AM
delphi276
Hi everybody,
I have a very interesting flicker problem that I cannot solve...
I have a TShape (SH) and a TCustomControl (CC). CC lies on top of SH. When
CC is being moved or resized (by the mouse) it is programmed to move or
resizeSH with it.
SH and CC are placed on a scrollbox, which is their parent and
scrollbox.DoubleBuffered is set to true. I made the form CC's and SH's
owner.
Now, when I MOVE CC (and thus SH) there is no flicker. But when I RESIZE CC
(and thus again also SH) there is!
Can anybody tell me why this is? If I make it so that CC (the top control)
still receives the mouse input but does not actually resize itself and I
make ONLY SH resize, there is no flicker either. So it seems that flicker
occurs because the two controls BOTH are being resized. But why is there
then no flicker when both are moved?
I'm very curious about any answers you might have.
Thanks for reading sofar,
Vinz.
 

Vincent Koopman writes:
repaint itself (because it is immobile within its container SH).
On a similar occasion (creating a TScrollImage) I noticed that panning
inside the scrollbox (by moving the origin of the contained image) produced
flicker. Panning by simply modifying the scrollbar positions didn't cause
any flicker.
Bottom line: Whenever you can, don't mess with children. Go after the
parents. :)
--
Ben
 

But CC is simply on top of SH. it is not a container as you say. I am using
code to resize SH That code gets executed when CC is being resized.
Is there a way CC can be a container perhaps?
Regards,
Vinz.
 

Vincent Koopman writes:
TPanel? Then you can align SH to alClient and manually resize CC in the
Panel's OnResize event handler.
--
Ben
 

It's for a designer program. Compare it with the IDE of Delphi, or Rational
Rose or stuff like that. So the user 'drops' a control or UML object
whatever and my component will automatically put a handle on top that is
responsible for showing the black dots around the edges etc.
So using a panel is not a very cool option. Can a panel be made seethrough
for example? And it makes the component heavier too...
"Ben Hochstrasser" <bhoc@surfeu123^H^H^H.ch>writes

Vincent Koopman writes:
Okay. What are you resizing first, the Shape or the Control? Because
resizing either of them will trigger some repaint event which usually
results in a flicker. (resizing the control will cause the system to
repaint the shape, but resizing the shape won't cause the system to repaint
the control, because the latter is on top anyway).
Sounds mighty scientific, eh? Anyway, try to swap the resize code for the
shape and the control and see if that helps any.
--
Ben
 

and it didn't seem to help.
Maybe I have to look at the repaints -again- ...
It seems that when the top-control is repainted the flicker occurs, not when
the bottom one is repainted.
Thanks for your help sofar mate,
Vinz.
 

Vincent Koopman writes:
flickering occurs? Will some flicker more than others? Would BeginUpdate/
EndUpdate help in such cases?
--
Ben
 

A move generates only two small bands of update area, while a resize
generates the complete shape surface as update area.
To get more control over update areas and repainting, you can try our
TVirtualScrollbox, which is specifically aimed towards that. Perhaps
DtpDocuments might also interest you, as a base for your own shapes,
completely flicker free and automatic support for rotation and
alpha-blending, as well as resize and rotate handles.
www.simdesign.nl/virtualscrollbox.html
www.simdesign.nl/dtpdocuments.html
Kind regards,
Nils Haeck
PS I am Dutch too.
"Vincent Koopman" writes news:XXXX@XXXXX.COM...

More information:
I did a test putting my TStretchControl over a TShape. TStretchControl =
class (TCustomControl)
The StretchControl has a property 'Control' where the Shape is being put.
The stretchcontrol gets the mouse input and as it moves it moves the shape
underneath with it. They both have the same parent and parent.doublebuffered
:= true;
Now I also created another TShape without a stretchcontrol on top. Same
parent. If I resized this one (using it is own mousedown/over events) there
was NO flicker. So the flicker seems to be caused by the stretchcontrol.
Settings Stretchcontrol.Doublebuffered := true doesn't help either.
Is that any help?
Cheers,
Vinz.
PS: BeginUpdate and EndUpdate do not apply here I think?
"Ben Hochstrasser" <bhoc@surfeu123^H^H^H.ch>writes

Vincent Koopman writes:
fires other events that make it flicker. (typically this happens when you
in the OnResize handler mangle the dimensions of the control without
temporarily disabling the OnResize event).
Dumb question: will it flicker only with the TShape underneath it or will
it flicker anyway?
--
Ben
 

Hi Vincent,
type
TStretchControl = class(TCustomControl)
{...}
protected
procedure CreateParams(var Params: TCreateParams); override;
{...}
end;
procedure TStretchControl.CreateParams(var Params: TCreateParams);
begin
inherited CreateParams(Params);
Params.ExStyle := Params.ExStyle + WS_EX_TRANSPARENT;
end;
Regards,
Jean-Marie
 

Hi JM,
The StretchControl is indeed transparent. Is that a problem or should that
help?
Regards,
Vinz.

J.M.