Qt does not position forms
lazarus / 32-Linux

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systemgvp · 2026-05-10 13:47

Situation:
 - kubuntu 26.04
 - lazarus 4.6
 - wayland

Using gtk3, qt5 or qt6, if I set a form position, it isn't executed.
Using gtk2, it is. Example:

1. I create a new empty application
2. I set position=poDesigned
3. I add a button and associate Form1.Left:=0;
4. I compile

If I click on button1, the form doesn't move, but stays in the center
of the screen.
What's missing? Why does it only work with GTK2?
On Kubuntu 25.10, Lazarus doesn't cause any problems, even on Windows.

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Alexx2000 · 2026-05-10 13:52

Wayland does not support changing window position. GTK2 executes using
Xwayland that's why it works.

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Thaddy · 2026-05-10 16:35

Basically it should NOT work, because Xwayland <> Wayland and by now
everybody knows that the cause is not Lazarus or has been sleeping
under a rock.
Everybody else also knows that Wayland has by now an extended API that
allows for Windowing management a bit better, but no one has
implemented it yet (that includes Lazarus, but also the rest of the
world except for tests).
It is rather pointless to discuss this any further. Just automatically
refer to the Wayland developers.

Btw: Qt6 is a lot better than GTK2.

And you @Alexx2000 already know all that. Don't even mention GTK2 is a
Qt thread.

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systemgvp · 2026-05-10 19:44

Yes, Qt6 is a lot better than GTK2, but unfortunately, I need to set
the shape's position in my application. Are you aware of any Wayland
scams?

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valdir.marcos · 2026-05-10 20:35

Quote from: systemgvp on May 10, 2026, 09:44:10 pmYes, Qt6 is a lot
better than GTK2, but unfortunately, I need to set the shape's
position in my application. Are you aware of any Wayland scams?
There is no immediate solution for Wayland.

The alternative, if possible in your case, would be to switch to
XLibre:

Ubuntu Repository for XLibre
https://github.com/xlibre-debian/ubuntu

About XLibre:
https://github.com/X11Libre/xserver

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zeljko · 2026-05-11 05:27

Quote from: systemgvp on May 10, 2026, 09:44:10 pmYes, Qt6 is a lot
better than GTK2, but unfortunately, I need to set the shape's
position in my application. Are you aware of any Wayland scams?

You can use Qt6 on same system where gtk2 is used, QT_QPA_PLATFORM=xcb
./yourapp should work.

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systemgvp · 2026-05-11 06:46

where should I put this string?

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zeljko · 2026-05-11 07:05

Put it as env variable just like I shown you for test. If that works
you can start your app via script. Adding it globally into your
$HOME/.bashrc isn't clever idea if you're on KDE Plasma wayland
because then everything will be x11/xcb...

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systemgvp · 2026-05-11 12:47

Sorry, but I don't understand where to insert the variable. Where is
this test?

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zeljko · 2026-05-11 13:00

In linux terminal: QT_QPA_PLATFORM=xcb ./yourapp , or if you run app
via lazrus debugger, Run -> Run parameters -> click second tab
"Environment", click Add button below, write env variable name
QT_QPA_PLATFORM, for value set xcb, now run your qt6 app.

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systemgvp · 2026-05-11 22:08

Thanks, both solutions work with QT6. I hope they are only a temporary
solution.

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dbannon · 2026-05-12 13:19

You can also add a command line parameter if thats more intuitive -

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i $> my-app
-platform xcb
Note its only one dash (should be two) and no '=' but the parameter is
filtered out by Qt before it gets to your app, so does not cause
problems with your command line parsing.

Davo

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Fred vS · 2026-05-12 15:32

Gemini propose this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
YourAppName; {$mode objfpc}{$H+} uses  {$IFDEF LINUX}  Unix, //
Required for fpGetEnv and fpSetEnv  {$ENDIF}  Interfaces, //
Initializes the Lazarus widgetset  Forms,   Unit1; {$IFDEF
LINUX}procedure CheckAndForceXCB;var  SessionType: String;begin  //
Retrieve the current desktop session type  SessionType :=
LowerCase(fpGetEnv('XDG_SESSION_TYPE'));    // If running on Wayland,
force Qt to fallback to XCB (via XWayland)  if SessionType = 'wayland'
then  begin    fpSetEnv('QT_QPA_PLATFORM', 'xcb', 1); 
end;end;{$ENDIF} begin  {$IFDEF LINUX}  // This must execute before
the Interfaces unit initializes Qt  CheckAndForceXCB;  {$ENDIF}  
Application.Initialize;  Application.CreateForm(TForm1, Form1); 
Application.Run;end.

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systemgvp · 2026-05-12 17:25

The problem is that I would like this solution to be already included
in the application, and not have to start the app manually every time

Quote from: zeljko on May 11, 2026, 03:00:17 pmIn linux terminal:
QT_QPA_PLATFORM=xcb ./yourapp , or if you run app via lazrus debugger,
Run -> Run parameters -> click second tab "Environment", click Add
button below, write env variable name QT_QPA_PLATFORM, for value set
xcb, now run your qt6 app.

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systemgvp · 2026-05-12 17:35

As always when using AI things don't work, in fact lazarus doesn't
recognize the fpGetEnv() and fpSetEnv() functions


Quote from: Fred vS on May 12, 2026, 05:32:55 pmGemini propose this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
YourAppName; {$mode objfpc}{$H+} uses  {$IFDEF LINUX}  Unix, //
Required for fpGetEnv and fpSetEnv  {$ENDIF}  Interfaces, //
Initializes the Lazarus widgetset  Forms,   Unit1; {$IFDEF
LINUX}procedure CheckAndForceXCB;var  SessionType: String;begin  //
Retrieve the current desktop session type  SessionType :=
LowerCase(fpGetEnv('XDG_SESSION_TYPE'));    // If running on Wayland,
force Qt to fallback to XCB (via XWayland)  if SessionType = 'wayland'
then  begin    fpSetEnv('QT_QPA_PLATFORM', 'xcb', 1); 
end;end;{$ENDIF} begin  {$IFDEF LINUX}  // This must execute before
the Interfaces unit initializes Qt  CheckAndForceXCB;  {$ENDIF}  
Application.Initialize;  Application.CreateForm(TForm1, Form1); 
Application.Run;end.

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Alexx2000 · 2026-05-12 18:06

Add this unit to uses before Interfaces unit:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
uQtWorkaround; {$mode objfpc}{$H+} interface implementation uses 
InitC, BaseUnix; function setenv(const name, value: pchar; overwrite:
cint): cint; cdecl; external clib; initialization 
setenv('QT_QPA_PLATFORM', 'xcb', 1); end.

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Fred vS · 2026-05-12 18:07

Quote from: systemgvp on May 12, 2026, 07:35:53 pmAs always when using
AI things don't work, in fact lazarus doesn't recognize the fpGetEnv()
and fpSetEnv() functions


Quote from: Fred vS on May 12, 2026, 05:32:55 pmGemini propose this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
YourAppName; {$mode objfpc}{$H+} uses  {$IFDEF LINUX}  Unix, //
Required for fpGetEnv and fpSetEnv  {$ENDIF}  Interfaces, //
Initializes the Lazarus widgetset  Forms,   Unit1; {$IFDEF
LINUX}procedure CheckAndForceXCB;var  SessionType: String;begin  //
Retrieve the current desktop session type  SessionType :=
LowerCase(fpGetEnv('XDG_SESSION_TYPE'));    // If running on Wayland,
force Qt to fallback to XCB (via XWayland)  if SessionType = 'wayland'
then  begin    fpSetEnv('QT_QPA_PLATFORM', 'xcb', 1); 
end;end;{$ENDIF} begin  {$IFDEF LINUX}  // This must execute before
the Interfaces unit initializes Qt  CheckAndForceXCB;  {$ENDIF}  
Application.Initialize;  Application.CreateForm(TForm1, Form1); 
Application.Run;end. 
Indeed, it should write:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses 
{$IFDEF LINUX}  BaseUnix, // Required for fpGetEnv and fpSetEnv 
{$ENDIF}
Bad gemini.

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systemgvp · 2026-05-12 18:31

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i {$IFDEF
LINUX}  SysUtils, InitC, BaseUnix, // Required for fpGetEnv and
fpSetEnv  {$ENDIF} {$IFDEF LINUX}//function setenv(name, value: PChar;
overwrite: Integer): Integer; cdecl; external 'libc.so.6';function
setenv(const name, value: pchar; overwrite: cint): cint; cdecl;
external clib; var SessionType: String;{$ENDIF}  {$IFDEF LINUX}  //per
risolvere il problema dei QT6 su wayland  SessionType :=
LowerCase(GetEnvironmentVariable('XDG_SESSION_TYPE'));  //if
SessionType = 'wayland' then setenv('QT_QPA_PLATFORM', 'xcb', 1);  
setenv('QT_QPA_PLATFORM', 'xcb', 1);  {$ENDIF} 
Code: [Select]ShowMessage(GetEnvironmentVariable('XDG_SESSION_TYPE')+'
--- '+GetEnvironmentVariable('QT_QPA_PLATFORM'));

if I compile and run I get "wayland --- ", it doesn't matter with both
functions.

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Alexx2000 · 2026-05-12 19:41

Yes, of course. Because GetEnvironmentVariable returns Free Pascal
environment. While we change C  environment which used by Qt. You can
check which session really used by Qt using IsWayland function from
QtInt unit.

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systemgvp · 2026-05-12 19:43

Unfortunately I'm an amateur programmer

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systemgvp · 2026-05-12 19:56

I'm using this solution which actually sets the variable
QT_QPA_PLATFORM=xcb

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i {$IFDEF
LINUX}function setenv(const name, value: pchar; overwrite: cint):
cint; cdecl; external clib;var SessionType: String;  EnvP: PPChar;
external name 'environ';function SetEnvironmentVariable(const Name,
Value: string): Boolean;begin  if setenv(PChar(Name), PChar(Value), 1)
<> 0 then  begin    Result := False;    Exit;  end;  // Forza FPC a
rileggere l'ambiente dalla libc  // Punta il puntatore interno di FPC
all'environ della libc  System.envp := EnvP;  Result :=
True;end;{$ENDIF}  {$IFDEF LINUX}    //per risolvere il problema dei
QT6 su wayland    SessionType :=
LowerCase(GetEnvironmentVariable('XDG_SESSION_TYPE'));    if
SessionType = 'wayland' then
SetEnvironmentVariable('QT_QPA_PLATFORM','xcb');  {$ENDIF
But I always get the same result. If I start the application from
lazarus (run), where the variable is preset, the form position is
displayed correctly. If I start the application outside of lazarus,
the application sets the variable correctly but doesn't move the form.

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dbannon · 2026-05-14 06:49

Well, I tried Alexx2000's method and found it worked perfectly, both
in Lazarus and in a stand alone app running on a Ubuntu26.04 VM.

However, we must remember that libxcb is just an interface to X as is
xlib. The nasty people who want to get rid of X will obviously remove
libxcb when they finally have their way.

I tested my app on that U26.04 box, patched and it works fine, windows
appear where they should be etc. So I then hid libxcb and my patched
app crashed because it cannot find libxcb, I'd hoped it would fall
back to xlib or even wayland.

So I tried an unpatched version, with libxcb hidden, it too crashed ! 
That means, even apps force to go via wayland have a dependency on
libxcb ??  So, I read that as saying we are safe having a hard
dependency on libxcb for the time being !

Better code might first test if libxcb is available before setting
that env var, only a few more lines of code ...

IMHO.

Davo

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zeljko · 2026-05-14 07:08

all qts in lazarus (qtint.pas) includes xlib unit and that's why it
crashes when there's no any x11 lib on system afair. Probably I'll
create an small unit with dynamic loading of libxcb (only needed
stuff) to get x11 part work (qtx11.inc), but to avoid crash on pure
wayland system without any x11 lib.

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dbannon · 2026-05-14 07:42

Well, I have not seen a system yet that does not have X at all. U26.04
does not let you switch Gnome to X but all the expected X libs are
still there. But for how long I ask ?

Mind you, looking at the size of the U26.04 install image, they
clearly don't care about disk space ....

As usual zeljko, thanks for what you do !

Davo