TListBox flickers when scrolling (laz 1.4.0)

[ncs-sniper]

Yes, XP, both 32 and 64bit.
I don't know much about LCL, but isn't it posssible to run default rendering only when OnDrawItem is not assigned and listbox does not have ownerdraw* style?
Something like

Code: Pascal  [Select][+][-]

1.     WM_ERASEBKGND:
2.       begin
3.         WindowInfo := GetWin32WindowInfo(Window);
4.         if ((WindowsVersion <= wvXP) or not ThemeServices.ThemesEnabled)
5.            and not (TCustomListBox(WindowInfo^.WinControl).Style in [lbOwnerDrawFixed,lbOwnerDrawVariable]) then
6.           // Standardbehavior for XP, or no themes
7.           Result := CallDefaultWindowProc(Window, Msg, WParam, LParam)
8.         else
9.         begin
10.           // Avoid unnecessary background paints to avoid flickering of the listbox
11.  
12.           Count := SendMessage(Window, LB_GETCOUNT, 0, 0);
13.           if Assigned(WindowInfo^.WinControl) and
14.             (TCustomListBox(WindowInfo^.WinControl).Columns < 2) and
15.             (Count <> LB_ERR) and (SendMessage(Window, LB_GETITEMRECT, Count - 1, Windows.LParam(@ARect)) <> LB_ERR) then
16.           begin
17.             Top := ARect.Bottom;
18.             Windows.GetClientRect(Window, ARect);
19.             ARect.Top := Top;
20.             if not IsRectEmpty(ARect) then
21.               Windows.FillRect(HDC(WParam), ARect, WindowInfo^.WinControl.Brush.Reference.Handle);
22.             Result := 1;
23.           end
24.           else
25.             Result := CallDefaultWindowProc(Window, Msg, WParam, LParam);
26.           Exit;
27.         end;
28.       end;    

I have not tested it properly, but it looks harmless to me.

[wp]

Code: Pascal  [Select][+][-]

1.     WM_ERASEBKGND:
2.       begin
3.         WindowInfo := GetWin32WindowInfo(Window);
4.         if ((WindowsVersion <= wvXP) or not ThemeServices.ThemesEnabled) then
5.         begin
6.           if Assigned(WindowInfo^.WinControl) and not
7.              (TCustomListbox(WindowInfo^.WinControl).Style in [lbOwnerDrawFixed, lbOwnerDrawVariable])
8.           then begin
9.             // Standardbehavior for XP, or no themes, no OwnerDraw
10.             Result := CallDefaultWindowProc(Window, Msg, WParam, LParam);
11.             exit;
12.           end
13.         end;
14.         // Avoid unnecessary background paints to avoid flickering of the listbox
15.         Count := SendMessage(Window, LB_GETCOUNT, 0, 0);
16.         if Assigned(WindowInfo^.WinControl) and
17.           (TCustomListBox(WindowInfo^.WinControl).Columns < 2) and
18.           (Count <> LB_ERR) and (SendMessage(Window, LB_GETITEMRECT, Count - 1, Windows.LParam(@ARect)) <> LB_ERR) then
19.         begin
20.           Top := ARect.Bottom;
21.           Windows.GetClientRect(Window, ARect);
22.           ARect.Top := Top;
23.           if not IsRectEmpty(ARect) then
24.             Windows.FillRect(HDC(WParam), ARect, WindowInfo^.WinControl.Brush.Reference.Handle);
25.           Result := 1;
26.         end
27.         else
28.           Result := CallDefaultWindowProc(Window, Msg, WParam, LParam);
29.         Exit;
30.       end;
31.  

This is better, your code may crash if the WinInfo^.WinControl is nil -- no idea, if this can happen.

I don't have XP, only on a virtual machine. The modification seems to run fine there. Please test thoroughly on your "real" XP - there are not so many XP users out there any more. Test also if non-ownerdrawn or unthemed listboxes are painted correctly with erased background. Post the result here, and I'll submit the new version as a patch to bugtracker.

[ncs-sniper]

Ok, will do tonight. But I can test it only on XP SP3 32b, XP 64b in virtual machine, Vista SP2 HomePrem. 32b and Win7 64b virtual (can't remember exact version). Do you thing it will be enough?

[wp]

Certainly, more than I had expected

[ncs-sniper]

Ok, I have tested it on attached program. I have tried it both with themes enabled and disabled where possible and of course 64bit builds. I have used code from your post with one change - it seems the background painting bug is manifesting itself even on winXP 64bit, which are AFAIK based on Win. Server 2003, so i have changed it like so:

Code: Pascal  [Select][+][-]

1. WindowsVersion <= wvServer2003

The results are:
Win XP SP3 32b - ok
Win XP 64b in VirtualBox - ok (after the mentioned change)
Win Vista Home Premium SP1 32b - ok
Win 7 Ultimate SP1 64b in VirtualBox - ok

[wp]

Perfect. I reopened the old bug report, Juha will certainly apply the patch soon.

[ncs-sniper]

Many thanks!