[Solved] Trackbar flickering

[Thaddy]

or

Code: Pascal  [Select][+][-]

1. var vRect : windows.Trect

rest looks fine.

[d7_2_laz]

Thaddy thanks, that’s true too    (i remember a bit of philosophical debate about somewhere else: “prefix it” vs. “change the order of units”).
Joanna: mine was from “Classes”,  which allows such a constructor as used. The other is from “Windows”, which does not.
A change of ordering might have impact elsewhere, so the prefixing is more sure. Sure as a direct assignment …

[Joanna]

Thanks everyone for the advice
I put the windows first in the uses section and it finally compiled.
Unfortunately the trackbar wiggles when resized. 
I’m wondering if I should try just hiding it while it’s being resized..

Nope that didn’t help either. It must be the win 7 operating system at fault.
Hopefully flickering will go away if I ever manage to port this to other platforms.

[440bx]

Nope that didn’t help either. It must be the win 7 operating system at fault.

Just for precision's sake...

It's extremely unlikely that the problem is in Win7, what's much more likely (read: extremely high probability) is that the trackbar implementation which is part of the Common Controls is buggy (not to mention poorly designed.)

As a historical note, in Win95, MS greatly extended the common controls, unfortunately it seems they gave the responsibility for implementing them to a group of high school students who had seen a computer in pictures only (and considering the result, the pictures were probably blurry!.)  The implementation was truly _sad_.  The library has improved over the years but, it still leaves a LOT  to desire and there are still plenty of "deficiencies" in it.  It's fairly obvious why Windows Explorer does not use the Common Controls instead it uses a custom implementation (much more capable and reliable.)

Anyway... the above is just FYI for whoever might be curious.

[Joanna]

I’m not surprised, however I lack the knowledge of how to fix it. I believe that there is also a tcdtrackbar control I don’t know if it would work better or not.

[d7_2_laz]

Joanna, just a thought besides:
ok, probably pre-paint / erasebkgnd isn’t responsibly involved here.
But what if the prog or component is flooded by too many paintings, maybe due to too many resize messages (remember, what wp did said: it would occur also if the size of the trackbar is fix).
What does this little test app say?
(Idea behind: if yes (too many messages), there should be found a hook).

Btw: you said you tried by “hiding it while it’s being resized”. -> How did you detect a “resize start” vs. a “resize end”?

EDIT: as a kind of reference, on Win10 i see such occurence of size/erase/paint messages as shown in the screenshot (having the trackbar aligned).

[lainz]

Try bgracontrols TBCTrackBarUpDown. Or custom drawn package...

[wp]

Let me test two standard ways to reduce flicker:

When I take d7_2_laz's code and add "Message.Msg := 1" (or 0) to the WMEraseBkGnd handler, the flicker is gone, even on Win 7, for both aligned and unaligned cases:

Code: Pascal  [Select][+][-]

1. procedure TTrackBar.WMEraseBkgnd(var Message: TLMEraseBkgnd);
2. var aRect : TRect;
3. begin
4.   Message.Msg := 1;
5. end;

An alternative possibility which seems to work in the same way is to override the CreateParams method and add a specific flag:

Code: Pascal  [Select][+][-]

1. procedure TTrackbar.CreateParams(var Params: TCreateParams);
2. begin
3.   inherited;
4.   Params.ExStyle := Params.ExStyle or $02000000;
5. end;

And finally, without using a sub-classed TTrackbar, this code basically could be added to the win32 interface:

Code: Pascal  [Select][+][-]

1. class function TWin32WSTrackBar.CreateHandle(const AWinControl: TWinControl;
2.   const AParams: TCreateParams): HWND;
3. var
4.   Params: TCreateWindowExParams;
5. begin
6.   // general initialization of Params
7.   PrepareCreateWindow(AWinControl, AParams, Params);
8.   // customization of Params
9.   with Params do
10.   begin
11.     pClassName := TRACKBAR_CLASS;
12.     WindowTitle := StrCaption;
13.     FlagsEx := FlagsEx or $02000000;
14.   end;
15.   // create window
16.   FinishCreateWindow(AWinControl, Params, false);
17.   Params.WindowInfo^.ParentMsgHandler := @TrackBarParentMsgHandler;
18.   Params.WindowInfo^.ThemedCustomDraw := true;
19.   Result := Params.Window;
20. end;

This procedure is in file lcl\interfaces\win32\win32wscomctrls.pp of your Lazarus installation. Add the highlighted line, and recompile your project (but before changing any lazarus file, always make a backup copy). I would appreciate if in particular the last method would be tested (for me it is working on Win 11 and Win 7 and does not seem to have side-effects).

[jamie]

WS_EX_COMPOSITED

That is a double buffer flag for a window, not supported in W2k, which people still use and I am not sure what effects it would have.

 Why not have a DoubleBuffer property in the control incase this does not work in all cases ?

[d7_2_laz]

WS_EX_COMPOSITED (0x02000000) – maybe DoubleBuffer hadn’t come into effect here without this flag; see:  https://devblogs.microsoft.com/oldnewthing/20171018-00/?p=97245

wp, I was somehow surprised that it helped here … being interested to know if without the “Exit(True)” (0 or 1, both seen as True? = “Windows, don’t paint, I’ll do this myself”) the amount of event calls was comparable. Could you tell or give a screenshot?
(On Win10 it had behaved fully normal, so I cannot see)
--
I’ ll try the change of the win32 interface later the day for to see if I notice a caveat.

[Joanna]

Thanks for the answers ?
Are any of the solutions cross platform without a dependency on the windows unit though?

[wp]

So far, the flicker was reported by you only for Windows (7). It is not clear at all whether the Trackbars on other platforms is flickering as well.

[d7_2_laz]

Sorry for the interrupt, short break back to the windows patch:
@wp, I tried your fix proposal on file lcl\interfaces\win32\win32wscomctrls.pp with Laz 3.0 Win64.
I couldn’t see any negative impacts as of now.
Also no benefits, of course, as there hadn’t be a negative behavior before …

But – just as one could expect, case trackbar not aligned – regarding the messages flow, after form’s resize there are no longer any trackbar’s resize/erasebkgnd/paint messages     // see image
Of course, if trackbar is aligned, a form’s resize will be followed by trackbar resize etc. -  All just as it should be …..

Btw, would interest me: in the OS scenario where the flicker had been seen:
before the fix, did you notice any strange message dispatching, an unexpected amount of resize/erasebkgnd/paint messages that differed noticeably from my first screenshot?

[wp]

Btw, would interest me: in the OS scenario where the flicker had been seen:
before the fix, did you notice any strange message dispatching, an unexpected amount of resize/erasebkgnd/paint messages that differed noticeably from my first screenshot?

No, nothing special, almost no change to the non-flickering Win11 (one more EraseBkGnd). The screenshots were taken after clearing the memo and clicking the button to increase the form width by 1. I set the Trackbar's Color to yellow to see that the background color in unthemed mode is still working after the patch - yes.

[wp]

Here are the screenshots for the same condition after the patch (could not send them in the previous post due to forum restrictions)

(Just to explain: Win 7 is flickering before the patch, Win 11 never; and "patch" refers to the change in TWin32WSTrackBar shown above).