Qt Interface

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This interface is based on Qt 4 and it's corresponding documentation here.

Other Interfaces

Platform specific Tips

Interface Development Articles

Quick start guide for Linux

As of lazarus 0.9.29 svn rev. 23858 2.1 bindings are needed, also bindings name is changed from libqt4intf to libQt4Pas !
IMPORTANT NOTE: for qt >= 4.7.XX libQt4Pas is compiled with -mstackrealign to avoid crashes, so download proper version from bindings page (binary bindings for 4.7 are marked) if your Qt version is 4.7 or higher.
The first thing to do is go to the official website of the bindings and download the binary Qt bindings. Copy the file libQt4Pas.so.5.2.1 + it's symlinks libQt4Pas.so.5.2 libQt4Pas.so.5 libQt4Pas.so to the directory /usr/lib/ or /usr/local/lib Now run "ldconfig" to update the linker cache. You can verify its success by running:

ldconfig -p | grep libQt4Pas.so.5.2.1

It must say something like:

       libQt4Pas.so (libc6) => /usr/local/lib/libQt4Pas.so

If it didn't work, you have to check the config files in /etc/ld.so.conf.d/ or the config file /etc/ld.so.conf, depending on your distro - it must include the path where you copied the libQt4Pas.so* files.

Hint: If you use a Debian based distribution, you can add the following repositories to your sources.list 
 deb http://ppa.launchpad.net/ximion/ppa/ubuntu karmic main 
 deb-src http://ppa.launchpad.net/ximion/ppa/ubuntu karmic main
 (For the keys use: gpg --recv-keys 4BF17E057EC6E8C3 --keyserver hkp://wwwkeys.eu.pgp.net ) 
The repositories contain the libQt4Pas.

Now compile the LCL for Qt. First open your normal gtk2 compiled Lazarus. Then go on the menu "Tools" --> "Configure Build Lazarus". Set LCL to "clean+build" and everything else to "None". Now select "Qt" and click on the "Ok" button. Next go to the menu "Tools" --> "Build Lazarus". Now the LCL is compiled for Qt.

To compile a project for Qt just select it as the target widgetset on the Compiler Options dialog.

Installing Qt 4

Most distributions now have packages for Qt 4. If your distribution is RPM-based you can search for a qt4 package here: http://rpm.pbone.net/index.php3/stat/2/simple/2
The supported Qt version is 4.5.0 or superior

Known problems on linux

  • glibc < 2.4 (older distros eg. FC3) users must compile qt-x11 with -no-sse or you have immediate segfaults.
  • Qt-4.4.1 if x11 < 7.0 & glibc < 2.4 (older distros) QPalette doesn't return good results for some palettes eg. QToolTip_palette().

Quick start guide for Mac OS X

Instructions on the Qt Interface Mac wiki page.

Quick start guide for PDAs and Smartphones

please write me

Quick start guide for Windows

There's nothing special to say for windows, it works just like on Linux and seems less buggy than win32 interface with some controls (TListView). Just rebuild Lazarus as it is mentioned for Linux, change to qt in compiler options and that's it.

Installing Qt 4

Download qt4 opensource edition from official website (http://www.qtsoftware.com/downloads/) eg. http://get.qt.nokia.com/qt/source/qt-win-opensource-4.6.3-mingw.exe , and you can download Qt4Pas5.dll from FPC Qt4 Binding. You can copy Qt4Pas5.dll in C:\windows\system32 if it isn't there, also qt4 dlls can be copied there, but maybe better approach would be to add qt4 bin directory into PATH.

Qt 4 Bindings

This interface utilizes Qt 4 bindings created by Den Jean. The bindings are a c++ library which exports the methods of the Qt objects as procedures. The library (around 800kb in Linux) consists of a single .so file that needs to be distributed with your LCL program.

You can find more information about those bindings on the official website and on FreePascal Qt4 binding.

It is being reported that it may be possible to link to Qt 4 directly, using some tricks. Many think it is not. This is yet to be tested. It is expected that any such binding will be compatible with the currently utilized one, so the interface code won´t have to be changed.

Compiling the bindings

It is not necessary to compile the bindings yourself if you plan to release a GPL software. GPL Binaries are available on Den Jean website. If you want to release non-GPL code, then you must compile the bindings yourself using the Commercial Edition of Qt. (Note: Qt-4.5 and higher are now available under the LGPL license)

Step 1 - To start with download all the files needed to compile the bindings.

  • Download the source code of the bindings. Go to the official website of the bindings. Link above.
  • Also Download Qt 4.5.2(3) or Qt 4.6.2(3) source code for the desired platform. This is the download page: [1]

Step 2 - Unpack all the files you downloaded. Enter the directory where you downloaded Qt 4.5(6).2(3) source code and use this command:

run qmake -query to inspect your Qt installation
qmake (creates Makefiles)
make install
use make clean to clean sources directory when switching qt versions

Step 3 - Go to the directory where you downloaded and extracted qt4pas sources and edit the file compile_lib.bash. Change the path for the Qt 4.5.2(3) source code. needed for old bindings.

Step 4 - Run the script called compile_lib.bash. Now you should have a file called libqt4intf.so.5.XXXX where XXXX is version of qt bindings, and its symbolic links libqt4intf.so.5 and libqt4intf.so needed for old bindings.With new bindings you'll get libQt4Pas.so.5.2.1 and symlinks libQt4Pas.so.5.2 libQt4Pas.so.5 libQt4Pas.so which must be in your library path (eg. copy it into /usr/lib).

Road map for the Qt 4 interface

Moved here: Roadmap#Widgetset_dependent_components

Conditional defines accepted by the Qt Interface

Moved here: LCL_Defines#Qt_defines


Much qt progress.png

More screenshoots
Qt Lazarus IDE running under linux (kernel 2.6.12, XOrg-6.8.2, KDE-3.4.0)
Qt Lazarus IDE running under Mac OS X 10.4.10


How to add a new control

For example TButton.

TButton is defined in lcl/buttons.pp. This is the platform independent part of the LCL, which is used by the normal LCL programmer.

Its widgetset class is in lcl/widgetset/wsbuttons.pp. This is the platform independent base for all widgetsets (qt, carbon, gtk, win32, ...).

Its qt interface class is in lcl/interfaces/qt/qtwsbuttons.pp:

 TQtWSButton = class(TWSButton)
   class function  CreateHandle(const AWinControl: TWinControl; const AParams: TCreateParams): TLCLIntfHandle; override;

Every WS class, that actually implements something must be registered. See the initialization section at the end of the qtwsXXX.pp unit:

 RegisterWSComponent(TQtButton, TQtWSButton);

TQtWSButton overrides CreateHandle to create a qt QPushButton. The code is short and should be easily adaptable for other controls like TCheckBox. Remember that all controls on the Qt widgetset have a helper class on qtprivate.pp, and it is also necessary to add a class for the new control. This isn´t difficult.

Also notice that DestroyHandle should be implemented to clean up memory utilized by the control.

Mailling List

There is a Lazarus - Qt mailling list for support and talk about the development of this interface here: http://lists.lazarus.freepascal.org/mailman/listinfo/qt