[swt/gtk development] Why you should type the odd /*int*/ comment after long

You might have noticed that a lot of code in SWT/GTK has that odd /*int*/ comment after a long declaration.

long /*int*/ list 

I turns out the comment is needed for backwards 32 bit support.

So in general you should put it in parameter declarations and in variable declarations:

//Parameter declaration:
Control [] _getChildren (long /*int*/ parentHandle)

//Variable declaration:
long /*int*/ list = OS.gtk_container_get_children (parentHandle);

This is especially important in OS.java which is used to generate C code.

How to tell if you are running Eclipse on Gtk2 or on Gtk3

When troubleshooting Eclipse bugs, I sometimes ask if you are running eclipse on gtk2 or gtk3.

Usually I can tell visually if Eclipse is running on Gtk2 or Gtk3, but this changes depending on your system theme.

In the about section

As Alexander Kurtakov pointed out and described in Lar’s article ,

Help -> About -> Installation Details -> Configuration Tab.

Look for something like:

It’s usually somewhere near line 84 ish. But you can copy the text and search for it in your text editor.

Note, if this line is missing altogether, you’re (very most likely) running Eclipse on Gtk2.

See what version is on your system

You can find out which version of gtk is installed on your system by running pkg-config (you might need to install it first). This gives you an indication of which version of gtk eclipse might be using.

pkg-config --modversion gtk+-3.0

Force Eclipse to use either gtk2 / gtk3

You can force Eclipse to use a certain version of gtk:

#Gtk3 forced:
export SWT_GTK3=1

#Gtk2 forced:
export SWT_GTK3=0

Under gtk3, the entry in the about section should be present like: org.eclipse.swt.internal.gtk.version=3.14.12


[edit 2016-09Sep-08Thu]
This is actually by far the most visited blog entry on my blog (20k+ views)
I reference this page quite often, I made a short/memorable url for it: http://bit.ly/gtk2orgtk3

How to compile various gtk3 versions and run eclipse Apps with those (for SWT Widget testing)


When developing SWT widgets, we need to test them on various GTK versions to ensure backwards compatibility.

There are some tricks and perks involved.

Get Gtk sources

  • Go to the gtk git repo and pull the code: https://git.gnome.org/browse/gtk+/
    (I recommend the https version: https://git.gnome.org/browse/gtk+)
    (if you don’t know how to use eclipse’s EGit, read this)
  • Check out the versions that you’re interested in (e.g 2.24, 3.10, 3.4, 3.8)
    These are found in major Linux distributions (e.g ubuntu 12..).
  • For the time being, check out the newest gtk version (e.g 3.10 at the time of writing).
    (It’s easier to build a newer version than an older one)
  • Open Terminal, go to your checked out gtk branch.
    Run the following commands:

    ./configure --enable-x11-backend --enable-wayland-backend
  • The first time you run the commands, you might run into errors telling you you’re missing something on your system. Inspect autogen.sh to see what it runs and then install the utilities with yum.
  • Now copy gtk to another place on your system. E.g ~/src/gtk2_24 This way you don’t have to recompile this business every time.
  • Now you can build the other versions and similarly copy them to ~/src/gtk*_*
  • NOTE ON gtk3.4 (and maybe older) The Wayland configuration makes certain things look more correct. But sometimes it makes building older versions (like gtk3.4) near impossible due to missing dependencies. In this case, run the configure without these:
     ./autogen.sh ./configure make 

Configure Eclipse to use the gtk you compiled

  • Edit your run-configuration of the code snippet that you want to run.
  • Navigate to “Environmental Variables”
  • Click on “Add”, type in:
    path: #your_compiled_gtk      //e.g /home/lufimtse/src/gtk3_10/gtk/.libs
  • Name your configuration (I reccomend appending gtk version, e.g “ControlExample (g3-10)”)
  • It should look something like this:
    Eclipse env var
  • Now run the configuration and you should see your application rendered in gtk*.*.
    You may note that it won’t have any styling:
    java app in compiled gtk
  • The lack of styling is due to the fact that there is no theaming.
    Now sometimes you might want the compiled gtk to use your system theame to see impact of themes on looks.
    To do so, do as above except run the configuration as following:

    ./configure --prefix=/usr --sysconfdir=/etc --enable-broadway-backend --enable-x11-backend --disable-wayland-backend

    In the interest of comparison: (left native look, right bare look)
    native vs bare

  • Lastly, in your source code, you might want to verify that you’re running the compiled gtk and not your own. Use this line of code:
    System.out.println("GTK Version: " + OS.gtk_major_version() + "." + OS.gtk_minor_version() + "." + OS.gtk_micro_version());