TListBox flickers when scrolling (laz 1.4.0)

[wp]

OK - here's a demo which shows the issue: Compile and run, just drag the scrollbar into the center and then quickly drag it up and down by 1 cm. You'll see occasional flickering of the first and last visible lines. Confirmed with Laz trunk/fpc 2.6.4 and with Laz 1.4/fpc 2.6.4. I can also confirm your observation that this did not occur earlier - I only have Laz 1.2 now, but there is no flicker with this version.

I looked through the svn logs, but did no find an obvious change.

ncs-sniper, please file a bug report, you can attach this demo if you want.

[BitBangerUSA]

tested wp's demo with Lazarus 1.2.4 / FPC 2.6.4 / Windows 7 Home Premium 64 bit - no flickering seen.

wp has gone 'above and beyond' on this one.

[wp]

Flicker is gone when the listbox responds to the WMEraseBackground message without actually clearing the background - see modified listbox in the right of the form in the attached demo.

BUT: the old version did not catch this message either but is working correctly. The bug must be somewhere else.

[balazsszekely]

I give up, I see no difference between listbox1 and listbox2.

[ncs-sniper]

I am glad at least someone was able to reproduce this. Yes, ignoring WMEraseBackground really helps.
I have also created more severe test (items are filled with pseudorandom noise, so redraw takes a lot of processing power and therefore time). Can anyone please test it?

[BitBangerUSA]

tested ncs-sniper prog - no flickering seen (run of the mill system) with Laz 1.2.4 / FPC 2.6.4 / Windwos 7 Home 64 bit.
much flickering on high-end system using Laz 1.4.

also got a dialog about heap on stopping the prog on high-end system - i've no clue as to importance.

[wp]

Yes, very dramatic effect, and no flicker with Laz 1.2

also got a dialog about heap on stopping the prog on high-end system - i've no clue as to importance

This is because heap trace is checked in the compiler options (Project options / Compiler options / Debugging / Use heaptrc unit...)

[ncs-sniper]

BitBangerUSA - it is set to be compiled in debug mode with heap tracking, that is why the window shows up. Just ignore it.
So at least two other users can see it too. Thanks for testing!

[BitBangerUSA]

wp and ncs-sniper - thanks for the info - i hadn't looked...

[airpas]

i see annoying flickering while scrolling or resizing the window , i use lazarus 1.5 / fpc 3.1.1 win7 32bits
also when using splitters too ,  i filed a report about that while ago

[wp]

airpas, I think your issue is different. It was reported for Laz 1.0.11 - I still have a 1.0 version lying around which does not show the listbox flicker.

[airpas]

my issue was with splitter .
i think the problem of flickering present in windows only . lcl-gtk/qt seems fine
 

[wp]

In r47451, a lot of work was done with the EraseBackground message in January. Maybe the bug slipped in this way.

I filed a bug report http://bugs.freepascal.org/view.php?id=28146

[ncs-sniper]

Many thanks for filing that bug report!
I have again tried it in linux (Lubuntu) - just to be sure, this time with the noise. And no, it really does not happen in linux.

[ncs-sniper]

I am watching the bug report (http://bugs.freepascal.org/view.php?id=28146) - catching the WM_EraseBackground does not solve it, it just hides it. I have tried this solution with interposer for TListBox in my project mentioned in the first post, and it does not flicker only because the individual items are very similar. If you have items that are visually distinct, it will flicker again (or better put, will produce artifacts).