[Resolved] Tlistview flicker problem if icon is updated

[ArminLinder]

Hi Lazarus/LCL/FPC experts,

just for fun I have tried to make a TListView Icon spin. On my test form I have a lone TListView (ViewStyle := vsReport, RowSelect := true), and I added a bunch of images to my SmallImages list, the images [0..5] contain the pictures of my rotating symbol. To check things out I let the symbol spin using a timer:

Code: Pascal  [Select][+][-]

1. procedure TForm1.Timer1Timer(Sender: TObject);
2.    begin
3.      if ListView1.Selected<>NIL then
4.         ListView1.Selected.ImageIndex:=(ListView1.Selected.ImageIndex + 1) mod 5;
5.    end;
6.  
7.  

The timer is set to 200ms, the principle works well, the icon of the selected row does indeed spin. But it seems like the LCL Listview redraws the whole row, not only the icon, causing the whole selected row flicker annoyingly.

Does anyone know a way to reduce the flicker, or at least modify the repaint behaviour in such a way that only the icon flickers, but not the entire row??

Thx, Armin.

(Lazarus 1.6.4 on Windows 7/Windows 10)

[jamie]

You could experiment a little with the Region property of the Canvas.
 
ListView1.Canvas.Region := SomewhereRegion

 The Region has a ClicpRect in it that limits the areas of painting.

The idea is to set it to the area of where the Images are updating.

 When you do this, all other areas should be ignored.
 
 Also, there is a property called Clipping:Boolean;

 Give it a go.


 

[ASerge]

On my test form I have a lone TListView (ViewStyle := vsReport, RowSelect := true), and I added a bunch of images to my SmallImages list, the images [0..5] contain the pictures of my rotating symbol.
...But it seems like the LCL Listview redraws the whole row, not only the icon, causing the whole selected row flicker annoyingly.

Windows 7, Lazarus 1.8 RC5. I do not see flicker with or without themes.
The code in Lazarus only changes the image:

Code: Pascal  [Select][+][-]

1. procedure TListItem.SetImageIndex(const AValue: TImageIndex);
2. begin
3.   if AValue = FImageIndex then
4.     Exit;
5.   FImageIndex := AValue;
6.   if WSUpdateAllowed then
7.     TWSCustomListViewClass(FOwner.FOwner.WidgetSetClass).ItemSetImage(FOwner.FOwner, GetIndex, Self, 0, FImageIndex);
8. end;
9.  
10. class procedure TWin32WSCustomListView.ItemSetImage(const ALV: TCustomListView; const AIndex: Integer; const AItem: TListItem; const ASubIndex, AImageIndex: Integer);
11. var
12.   lvi: TLvItem;
13. begin
14.   if not WSCheckHandleAllocated(ALV, 'ItemSetImage') then
15.     Exit;
16.   lvi.Mask := LVIF_IMAGE;  // <- ONLY IMAGE
17.   lvi.iItem := AIndex;
18.   lvi.iSubItem := ASubIndex;
19.   lvi.iImage := AImageIndex;
20.   ListView_SetItem(ALV.Handle, lvi);
21. end;

By the way, if there are 6 images ([0..5]), then it's better to use them all: ...) mod 6.

[jamie]

Maybe ListView1.DoubleBuffered := True;  Will help?

[ArminLinder]

Hi Jamie&Serge,

thank you for your quick replies. See attached video --> it DOES flicker :-). DoubleBuffer is already on, doesn't seem to change anything.

You think an upgrade to 1.8 may help, has the LCL code been worked over?

Armin.

Here is the complete source I use for testing, is a snipped from a larger project, so don't wonder about the initialization routine:

Code: Pascal  [Select][+][-]

1. unit unit2;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls,
9.   ComCtrls, ExtCtrls;
10.  
11. type
12.  
13.   { TForm1 }
14.  
15.   TForm1 = class(TForm)
16.     Button1: TButton;
17.     Button2: TButton;
18.     ImageList1: TImageList;
19.     ListView1: TListView;
20.     Timer1: TTimer;
21.     procedure Button2Click(Sender: TObject);
22.     procedure FormCreate(Sender: TObject);
23.     procedure ListView1Click(Sender: TObject);
24.     procedure Timer1Timer(Sender: TObject);
25.   private
26.     { private declarations }
27.   public
28.     { public declarations }
29.   end;
30.  
31. var
32.   Form1: TForm1;
33.  
34. implementation
35.  
36. {$R *.lfm}
37.  
38. { TForm1 }
39.  
40. procedure TForm1.ListView1Click(Sender: TObject);
41.  
42. begin
43. end;
44.  
45. procedure TForm1.Timer1Timer(Sender: TObject);
46. begin
47.   if ListView1.Selected<>NIL then
48.      ListView1.Selected.ImageIndex:= (ListView1.Selected.ImageIndex + 1) mod 5;
49. end;
50.  
51. procedure TForm1.Button2Click(Sender: TObject);
52.  
53. begin
54.      Timer1.Enabled := not Timer1.Enabled;
55. end;
56.  
57. procedure TForm1.FormCreate(Sender: TObject);
58.  
59. var i : integer;
60.     ListItem: TListItem;
61.     Col:TListColumn;
62.  
63. begin
64.   With ListView1 do
65.    begin
66.    DoubleBuffered := true;
67.    RowSelect := true;
68.    if Columns.Count = 0 then
69.       begin
70.         Col := Columns.Add;
71.         Col.Caption := '';
72.         Col.AutoSize := true;
73.         Col := Columns.Add;
74.         Col.Caption := '1st Subitem';
75.         Col.Width := 100;
76.         Col := Columns.Add;
77.         Col.Caption := '2nd SubItem';
78.         Col.Width := 100;
79.       end;
80.    clear;
81.    for i := 0 to 100 do
82.      begin
83.        ListItem := Items.Add;
84.        ListItem.ImageIndex:=1;
85.        ListItem.SubItems.Add('Item ' + IntToStr(i));
86.        ListItem.SubItems.Add('SubItem ' + IntToStr(i));
87.      end;
88.    end;
89. end;
90.  
91. end.
92.  

[balazsszekely]

@Nimral
You should also attach the small test project, apparently there is an ImageList in your project.  Also tell us when the flicker occurs.

[ArminLinder]

@Nimral
You should also attach the small test project, apparently there is an ImageList in your project.  Also tell us when the flicker occurs.

Hi GetMem,

--> Attachment!

Itemlist is pretty straightforward, I took an icon and made a few rotated versions of it. Not even the whole 360° yet, wanted to test first.

Armin.

[balazsszekely]

@Nimral

Testing environment:
1. Win7(64 bit), Lazarus Trunk, FPC 3.0.2
2. Linux Mint Cinnamon(64 bit), Lazarus Trunk, FPC Trunk
3. XP(32 bit), Lazarus 1.8RC5, FPC 3.0.4

I see no flicker whatsoever. The icons are rotating nicely.

[ArminLinder]

Hi GetMem,

Thanks for your feedback. Seems I need to look deeper into that issue tomorrow. As you see in my video, there definitiely is a flicker problem, but if you say, it's not standard LCL behaviour, there must be another reason, why it appears on my system.

I'll put my demo code through various demo machines tomorrow, let's see if there is some dependency on graphics hardware or driver.

Greetz,

Armin.

[balazsszekely]

but if you say, it's not standard LCL behaviour, there must be another reason, why it appears on my system.

All I'm saying is I cannot reproduce the issue in a newer version of Lazarus. The bug most likely was already fixed.

[ArminLinder]

Hi guys,

I put the program through some other computers I had lying around, as well as through several virtual machines (MS Remote Desktop), and the problem does not appear on any system but my development computer. I tried both 1.6.4 and 1.8 RC4. Since my development system is a virtualized (VMWare 12) system I suspect that it is most likely a problem with the VMWare VGA driver.

This is somewhat surprising, I usually don't have any notable screen refresh problems in VMware, that's why it didn't come to my mind to suspect a problem with the virtualization.

Sorry guys for having bugged you, and thanks for your helpful hints.

Armin.