Date Thu 30 June 2011

Getting up and running with QtCreator and QGIS

Firstly let me preface this article by saying that I am not a huge fan of IDEs - I've been using VIM for more than a decade and it's a tough habit to break. That said, QtCreator has a lot going for it (including a special concession to VIM users) and it is a lot easier to use for debugging that crusty old gdb on the command line. So in the article below I am going to run through an optimal (from my point of view anyway) setup for using QtCreator to build, develop and debug QGIS with.

QtCreator is a newish IDE from the makers of the Qt library. With QtCreator you can build any C++ project, but it's really optimised for people working on Qt(4) based applications (including mobile apps). Everything I describe below assumes you are running Ubuntu 11.04 'Natty'.

Installing QtCreator

This part is easy:

sudo apt-get install qtcreator qtcreator-doc

After installing you should find it in your gnome menu.

Setting up your project

I'm assuming you have already got a local Quantum-GIS clone containing the source code, and have installed all needed build dependencies etc. There are detailed in instructions on doing that here:

http://github.com/qgis/Quantum-GIS/blob/master/CODING

On my system I have checked out the code into:

$HOME/dev/cpp/Quantum-GIS

and the rest of the article is written assuming that, you should update these paths as appropriate for your local system.

On launching QtCreator do:

File->Open File or Project

Then use the resulting file selection dialog to browse to and open this file:

  $HOME/dev/cpp/Quantum-GIS/CMakeLists.txt



|Open the top level CMakeLists.txt|

Next you will be prompted for a build location. I create a specific build dir for QtCreator to work in under:

$HOME/dev/cpp/Quantum-GIS/build-master-qtcreator

Its probably a good idea to create separate build directories for different branches if you can afford the disk space.

Build location

Next you will be asked if you have any CMake build options to pass to CMake. We will tell CMake that we want a debug build by adding this option:

 -DCMAKE_BUILD_TYPE=Debug


|CMake Parameters|

That's the basics of it. When you complete the Wizard, QtCreator will start scanning the source tree for autocompletion support and do some other housekeeping stuff in the background. We want to tweak a few things before we start to build though.

Setting up your build environment

Click on the 'Projects' icon on the left of the QtCreator window.

Project properties

Select the build settings tab (normally active by default).

Build settings

We now want to add a custom process step. Why? Because QGIS can currently only run from an install directory, not its build directory, so we need to ensure that it is installed whenever we build it. Under 'Build Steps', click on the 'Add Build  Step' combo button and choose 'Custom Process Step'.

Add custom step

Now we set the following details:

  Enable custom process step [yes]
  Command: make
  Working directory: $HOME/dev/cpp/Quantum-GIS/build-master-qtcreator
  Command arguments: install

|Creating a custom process step|

You are almost ready to build. Just one note: QtCreator will need write permissions on the install prefix. By default (which I am using here) QGIS is going to get installed to /usr/local. For my purposes on my development machine, I just gave myself write permissions to the /usr/local directory.

To start the build, click that big hammer icon on the bottom left of the window.

The build icon

Setting your run environment

As mentioned above, we cannot run QGIS from directly in the build directly, so we need to create a custom run target to tell QtCreator to run QGIS from the install dir (in my case /usr/local/). To do that, return to the projects configuration screen.

Project properties

Now select the 'Run Settings' tab

The run settings tab

We need to update the default run settings from using the 'qgis' run configuration (shown below) to using a custom one.

Default executable which we want to override

Do do that, click the 'Add v' combo button next to the Run configuration combo and choose 'Custom Executable' from the top of the list.

Add a custom executable

Now in the properties area set the following details:

Executable: /usr/local/bin/qgis
Arguments :
Working directory:
$HOME
Run in terminal: [no]
Debugger: C++ [yes]
          Qml [no]

Then click the 'Rename' button and give your custom executable a meaning full name e.g. 'Installed QGIS'

Custom executable properties

Running and debugging

Now you are ready to run and debug QGIS. To set a break point, simply open a source file and click in the left column.

|Adding a breakpoint|

Now launch QGIS under the debugger by clicking the icon with a bug on it in the bottom left of the window.

Run QGIS in debug mode

Conclusion

There are a few other handy tips and tricks you can do in QtCreator which I will try to cover in a future article. With the information presented above you should at least be on your way to having QGIS setup in QtCreator. Having an interactive debugger at your fingertips is a great way to learn to code in QGIS as it is easy to follow the logic flow from one class / to the next. It also makes it easy for casual developers to dive in and find a bug that is irritating them and either send us a comprehensive bug report or send use a fix :-).


Comments

comments powered by Disqus