Re: [Lazarus] Clipboard Data Goes Away

[Anthony Walter via lazarus]

Colin,

After some research I've found that LCL Gtk2 isn't using gtk_clipboard_x
functions, rather it's using gtk_selection_x functions. There are
gtk_clipboard functions to do the same thing as gtk_selection functions,
but because the gtk_clipboard functions are not being used, the
gtk_clipboard_store function does not work with the LCL Gtk2 clipboard.
I've written a mini clipboard class that allows for multiple formats on the
clipboard at the same time and it works well and also allows clipboard data
to persist after my application closes, but my design does not conform to
the WS (widgetset) model used by the LCL, and thus operates outside of the
LCL.

In the end, I'm confident that if LCL Gtk2 were written to use
gtk_clipboard functions instead of gtk_selection functions, the problem
could be fixed. I do not mean to place blame on any of the LCL Gtk2
developers, as the gtk_clipboard functions were most likely developed and
released sometime after the first few iterations of Gtk2. Particularly, the
gtk_clipboard_set_can_store did not exist until Gtk 2.6.
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Re: [Lazarus] Clipboard Data Goes Away

[C Western via lazarus]

(You have definitely educated me)

I tried something similar on one of my own applications, and it doesn't 
work for me either. I suspect sometihing more elaborate is required, as 
I don't think the LCL does calls gtk_clipboard_set_text, even for text. 
Reading the documentation for gtk_clipboard_set_can_store suggests this 
should be called also, but a quick trial of this didn't work either.


Colin



On 01/04/2021 09:35, Anthony Walter via lazarus wrote:

Here is a follow-up.

I wrote a simple test using LCL Gtk2 and gtk_clipboard_store. This 
test allows the clipboard data to persist after my program exited. 
Button1 click sets the clipboard data. If Button2 clicked the data 
will persist after the program exits. If Button2 is not clicked, the 
data does not persist. Curiously, as the LCL Gtk2 currently stands, 
gtk_clipboard_store() does not work. I suspect the LCL is not 
using the same GdkAtom clipboard as returned by 
gtk_clipboard_get(GDK_SELECTION_CLIPBOARD).


uses
  Gtk2, Gdk2;

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
var
  S: string;
begin
  S := Edit1.Text;
gtk_clipboard_set_text(gtk_clipboard_get(GDK_SELECTION_CLIPBOARD), 
PChar(S), Length(S))

end;

procedure TForm1.Button2Click(Sender: TObject);
begin
gtk_clipboard_store(gtk_clipboard_get(GDK_SELECTION_CLIPBOARD));
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
  Close;
end;




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Re: [Lazarus] Clipboard Data Goes Away

[Anthony Walter via lazarus]

Here is a follow-up.

I wrote a simple test using LCL Gtk2 and gtk_clipboard_store. This test
allows the clipboard data to persist after my program exited. Button1 click
sets the clipboard data. If Button2 clicked the data will persist after the
program exits. If Button2 is not clicked, the data does not persist.
Curiously, as the LCL Gtk2 currently stands, gtk_clipboard_store() does not
work. I suspect the LCL is not using the same GdkAtom clipboard as returned
by gtk_clipboard_get(GDK_SELECTION_CLIPBOARD).

uses
  Gtk2, Gdk2;

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
var
  S: string;
begin
  S := Edit1.Text;
  gtk_clipboard_set_text(gtk_clipboard_get(GDK_SELECTION_CLIPBOARD),
PChar(S), Length(S))
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  gtk_clipboard_store(gtk_clipboard_get(GDK_SELECTION_CLIPBOARD));
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
  Close;
end;

>
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Re: [Lazarus] Clipboard Data Goes Away

[Anthony Walter via lazarus]

Thanks Michael.

It looks as if this problem was fixed in Gtk2 by version 2.6. The
developers added this function to work around this problem:

void gtk_clipboard_store (GtkClipboard *clipboard);

Stores the current clipboard data somewhere so that it will stay around
after the application has quit.

Parameters
clipboard

a GtkClipboard

Since: 2.6

Looking at the LCL source, it seems the Gtk3 LCL is using this function to
save the clipboard data after the program exists, but it's not being used
in the Gtk2 LCL. With this function, the problem I've described should be
fixable in LCL Gtk2.
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Re: [Lazarus] Clipboard Data Goes Away

[Michael Van Canneyt via lazarus]

On Thu, 1 Apr 2021, Anthony Walter via lazarus wrote:


Perhaps there is a Linux service that can be used by applications to hand
over and take ownership of clipboard data, and applications such as those I
mentioned are using it in order to solve the problem I am describing?



See my earlier reply for some links.

Michael.
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Re: [Lazarus] Clipboard Data Goes Away

[Anthony Walter via lazarus]

Perhaps there is a Linux service that can be used by applications to hand
over and take ownership of clipboard data, and applications such as those I
mentioned are using it in order to solve the problem I am describing?
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Re: [Lazarus] Clipboard Data Goes Away

[Michael Van Canneyt via lazarus]

On Thu, 1 Apr 2021, Anthony Walter via lazarus wrote:


I noticed a recent discussion touching on this problem posted by Bo
Berglund on November 20, 2020 to this same mailing list.

Andreas Schneider replied in that thread, 'Pasting basically asks the
application that "copied" it to get the content. If that app is gone in the
meantime, there's nothing to paste anymore.'

Also, Colin Western replied this is how Linux applications work, 'the data
is kept with the source program, so goes when the program closes'.

I disagree.

I've tested several Gtk2 applications, including older versions of Gimp
and  Geany. Both these programs have clipboard copy functions and the data
on the clipboard from those applications my tests show their clipboard data
persists after they have been closed. So it would seem that Gtk2 the
clipboard works correctly and handles persisting data after an application
has exited.

I stepped through the LCL source and it looks like the clipboard code is
using some Gtk clipboard functions, and not using X windows functions,
thereby introducing a possible problem, but I am unsure if the LCL is using
the Gtk clipboard correctly. That is, the LCL might be using some Gtk
clipboard functions which seem to work well, but exhibit the problematic
behaviour I've described.


I think the programs you tested use some extra functions, because as these
2 persons already said: under X11, the selection is owned by the program,
not by X11.

See e.g.

https://www.uninformativ.de/blog/postings/2017-04-02/0/POSTING-en.html
https://wiki.ubuntu.com/ClipboardPersistence

for an explanation.

Basically: if you don't communicate with a persistent clipboard app, then
nothing will happen to persist your selection.

Michael.

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Re: [Lazarus] Clipboard Data Goes Away

[Colin Western via lazarus]

I am very confident that the X11 behaviour is that the data goes with the 
application. It might be that more recent desktops/toolkits have some work 
around, but the gtk2 functions lazarus uses only copy data externally when 
asked for by an X11 messaage and this is all gtk2 provides.

Colin


> On 01/04/2021 08:26 Anthony Walter via lazarus 
>  wrote:
> 
> 
> I noticed a recent discussion touching on this problem posted by Bo Berglund 
> on November 20, 2020 to this same mailing list.
> 
> Andreas Schneider replied in that thread, 'Pasting basically asks the 
> application that "copied" it to get the content. If that app is gone in the 
> meantime, there's nothing to paste anymore.'
> 
> Also, Colin Western replied this is how Linux applications work, 'the data is 
> kept with the source program, so goes when the program closes'.
> 
> I disagree.
> 
> I've tested several Gtk2 applications, including older versions of Gimp and 
> Geany. Both these programs have clipboard copy functions and the data on the 
> clipboard from those applications my tests show their clipboard data persists 
> after they have been closed. So it would seem that Gtk2 the clipboard works 
> correctly and handles persisting data after an application has exited.
> 
> I stepped through the LCL source and it looks like the clipboard code is 
> using some Gtk clipboard functions, and not using X windows functions, 
> thereby introducing a possible problem, but I am unsure if the LCL is using 
> the Gtk clipboard correctly. That is, the LCL might be using some Gtk 
> clipboard functions which seem to work well, but exhibit the problematic 
> behaviour I've described.
> -- ___ lazarus mailing list 
> lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
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Re: [Lazarus] Clipboard Data Goes Away

[Anthony Walter via lazarus]

I noticed a recent discussion touching on this problem posted by Bo
Berglund on November 20, 2020 to this same mailing list.

Andreas Schneider replied in that thread, 'Pasting basically asks the
application that "copied" it to get the content. If that app is gone in the
meantime, there's nothing to paste anymore.'

Also, Colin Western replied this is how Linux applications work, 'the data
is kept with the source program, so goes when the program closes'.

I disagree.

I've tested several Gtk2 applications, including older versions of Gimp
and  Geany. Both these programs have clipboard copy functions and the data
on the clipboard from those applications my tests show their clipboard data
persists after they have been closed. So it would seem that Gtk2 the
clipboard works correctly and handles persisting data after an application
has exited.

I stepped through the LCL source and it looks like the clipboard code is
using some Gtk clipboard functions, and not using X windows functions,
thereby introducing a possible problem, but I am unsure if the LCL is using
the Gtk clipboard correctly. That is, the LCL might be using some Gtk
clipboard functions which seem to work well, but exhibit the problematic
behaviour I've described.
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Re: [Lazarus] Clipboard Data Goes Away

[Colin Western via lazarus]

This is the way the linux clipboard works - the data is kept with the source 
program, so goes when the program closes.

Colin

> On 01/04/2021 07:58 Anthony Walter via lazarus 
>  wrote:
> 
> 
> On Linux Gtk2, over time I have noticed a problem where data copied to the 
> clipboard by a Lazarus application does not persist on the clipboard after 
> the Lazarus program has exited.
> 
> While writing this application 
> (https://cache.getlazarus.org/images/desktop/capture-tool.png) that captures 
> image data to the clipboard, the data on the clipboard is only available to 
> other applications while mine is running. If I exit my program the clipboard 
> data goes away. The same problem occurs if the clipboard data is text rather 
> than a bitmap.
> 
> Is this a known issue on Linux LCL Gtk2? Is there a workaround?
> 
> Thank you for your attention.
> 
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[Lazarus] Clipboard Data Goes Away

[Anthony Walter via lazarus]

On Linux Gtk2, over time I have noticed a problem where data copied to the
clipboard by a Lazarus application does not persist on the clipboard after
the Lazarus program has exited.

While writing this application
 that
captures image data to the clipboard, the data on the clipboard is only
available to other applications while mine is running. If I exit my program
the clipboard data goes away. The same problem occurs if the clipboard data
is text rather than a bitmap.

Is this a known issue on Linux LCL Gtk2? Is there a workaround?

Thank you for your attention.
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