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SWT/Devel/Gtk/Dev guide

< SWT‎ | Devel‎ | Gtk
Revision as of 09:14, 25 April 2016 by Ericwill.redhat.com (Talk | contribs) (SWT and GTK versions)

Contents

The Comprehensive Guide to SWT Development for Linux/Gtk

This is a work in progress. Certain sections may be missing, or incomplete.

About SWT

SWT is the layer between PlatformUI and the underlying Gtk2 or Gtk3 of the system. It can be launched to use Gtk2 or Gtk3, but cannot use them both at the same time. Communication from Java (SWT layer) to C (native Gtk layer) occurs through calls defined in OS.java. The image below describes this hierarchy better:

SWT call hierarchy.png

You will learn:

  • How to configure your machine (Eclipse/Git) to contribute SWT patches
  • Info on building .SO images to run snippets with newest SWT Master
  • Info on Gtk Versions, compiling various Gtk Versions
  • How to add your own gtk_ methods to OS.java
  • Tips on SWT Development, how to navigate the code base
  • Understanding the underlying glue (swtFixed) between SWT/Java and Gtk/C
  • Learn how to compile various Gtk versions for testing with SWT
  • Learn how to make a Gtk application in Eclipse & how to debug it
  • Learn to debug Gtk itself
  • Learn how to debug the native Gtk (C) part of a running SWT (Java) application
  • Learn how to debug the swtFixed custom C code of a running SWT (Java) application

Upon completion of this document, hopefully you will know SWT-fu (as in kung-fu).

Knowledge Pre-requisites

  • Solid Java knowledge: from class inheritence to multi-threading
  • Some C experience: know thy pointers and make files
  • Gtk background highly recommended but can be learned
  • Eclipse: knowing how to use Eclipse is quite essential. But you don't have to know about JFace/PlatformUI/RCP development internals
  • Git: for example you should know the difference between merge and rebase. But all git-bits can be learned

Communication and support

SWT Community

If you have questions, you should post them to:

 platform-swt-inbox@eclipse.org

It's also a good idea to sign up for the SWT mailing list. There are #swt-gtk and #eclipse-dev channels on Freenode (IRC) as well.

Following SWT bugs in Bugzilla

Whenever you work on a project, you should consider following the default assignee of the project in Bugzilla. This way you find out about new issues and what issues get worked on. To do so, go to bugzilla https://bugs.eclipse.org/ -> Preferences -> Email preferences, and add the email below to your watch list:

 platform-swt-inbox@eclipse.org

SWT Development Environment Setup

There is an important distinction when running SWT: using the pre-compiled .JAR file, or using the source code in your local Git repository.

.JAR

You can download the SWT .JAR file, and add it as a library in your project: https://www.eclipse.org/swt/. However, when you make changes to the SWT source code, these changes will not be visible when running SWT. This is only useful if you develop 'using' SWT, but not SWT itself.

Source code

To develop SWT itself, being able to run SWT using the changes made to the source code is important. The process to do is lengthy, but valuable.

Add the SWT project to the build path

In order to run snippets with the SWT source code, you will need to add the SWT project to the snippets' project build path. To do this:

  • Right click the SWT snippets project in the Package Exlporer
  • Select "Properties"
  • Select "Java Build Path" on the right hand side
  • Select the "Projects" tab and click "Add..."
  • Select the SWT project and click "OK"

Install the SWT Developer Tools Eclipse Plugin

SWT developer tools automatically builds the custom C code that SWT uses to work with Gtk. Without the tools, you cannot develop SWT. Install the latest from the Eclipse update site: https://www.eclipse.org/swt/updatesite.php

Remember to re-install these tools if you re-install Eclipse.

Eclipse git (Egit)

Eclipse git is used to compare SWT files against older versions. Not strictly necessary, but highly recommended as it's sometimes easier to use Git through Eclipse than it is through the command line. If you are on Fedora, run:

 sudo dnf install eclipse-git

SWT source code and binary repositories

Check out the repositories holding the SWT sources and binaries. I usually do this from inside Eclipse, but you can also clone things from the command line. The URI's for the repositories are:

 git://git.eclipse.org/gitroot/platform/eclipse.platform.swt.git
 git://git.eclipse.org/gitroot/platform/eclipse.platform.swt.binaries.git

Modify the .classpath files

At first you might get many many errors. You first have to tell the project, that you are on Linux/Gtk for things to compile/run properly. Specifically for Gtk, you must do the following:

  • Open the 'Navigator' view (not package explorer)
  • Under 'org.eclipse.swt' look for the .classpath files
  • Rename .classpath_gtk to .classpath
  • Clean up projects (in Eclipse, Project -> Clean)
  • Now run a test snippet or ControlExample.java, it should work without the compilation errors

Configure git for review

To contribute to SWT, you need to modify your Git config to be able to push to Gerrit, which is the Eclipse Project's review system. Open your Git root, navigate to the SWT repository, and open the Git config file with a text editor . On my system it looks like this:

 ~/git/eclipse.platform.swt/.git/config

Add review branch: (adjust for your own user name instead of 'lufimtsev'):

 [remote "review"]
   url = ssh://lufimtsev@git.eclipse.org:29418/platform/eclipse.platform.swt.git
   push = HEAD:refs/for/master

Under the existing master, add 'rebase = true':

 [branch "master"]
   rebase = true

Add your name and email for signing off commits:

 [user]
   name = Lev Ufimtsev
   email = lufimtse@redhat.com

You can now push your changes to the review branch (Gerrit) for review:

 git push review

Enable 32/64 bit checking by SWT Tools

The Java source code has to work on both 32 and 64 bit machines. On 32 bit machines, calls to Gtk that use long in the parameter will not compile. All such longs should have an /*int*/ annotation after it. For example:

 //This will cause a 32 bit build to fail:
 void gtk_css_provider_load_from_css (long context, String css)  { .. }
  //                                      ^ missing /*int*/
 
 //Every 'long' should followed by a '/*int*/' like so:
 void gtk_css_provider_load_from_css (long /*int*/ context, String css)

To avoid missing these things by accident, SWT Tools can automatically check these things and mark them as errors. This functionality must first be enabled though. By now you should have SWT Developer tools already installed. To enable checking automatically:

  • Right click on the 'org.eclipse.swt' project.
  • From the drop down menu, enable 'SWT Tools -> Report 32/64 bit problems'
  • Now if you don't include the /*int*/ a warning will be thrown in your the problem view

References

https://www.eclipse.org/swt/fixbugs.php

GTK .SO bindings

About

You checked out two SWT repos: SWT and SWT binaries. The SWT binaries contain ready-build SO files to be used with built with the SWT source code. Sometimes you need to add native GTK functions to OS.java, allowing you to use those new functions in the SWT (Java) source code. After any changes to OS.java, you need to rebuild the Gtk .SO bindings. Otherwise SWT will complain about "unsatisfied link errors" between the SWT source code and the binaries.

Prerequisites

  • SWT Tools
  • Gtk libraries:
 #non-fedora, install these packages:
 gtk3-devel gtk2-devel libXtst-devel mesa-libGLU-devel libXt-devel
 //you may also need "X Software Development".
 
 #On Fedora, you can auto install all libs needed for Gtk2 building via:
 sudo dnf builddep gtk2   
 sudo dnf builddep gtk3   
 sudo dnf groupinstall "X Software Development"

Building

This process can (and is) automated into a script, but knowing what is going on in the background is also important.

The below assumes that you checked things out into:

 ~/git/
  • Clean the org.eclipse.swt project in Eclipse (Project -> Clean)
  • Inside Eclipse, run build.xml from org.eclipse.swt.gtk.linux.x86_64/build.xml and make sure "build.jars" and "build_libaries" are selected
  • You will get some error messages, this is fine. Proceed with the next step. The error message will look similar to this:
 /home/lufimtse/git/eclipse.platform.swt/bundles/org.eclipse.swt/buildSWT.xml:918: The following error occurred while executing this line:
 /home/lufimtse/git/eclipse.platform.swt/bundles/org.eclipse.swt/buildSWT.xml:890: javax.script.ScriptException: ReferenceError: "importClass" is not defined in <eval> at line number 3
  • Open terminal, go to /bin/library inside your SWT repository:
 cd ~/git/eclipse.platform.swt/bundles/org.eclipse.swt/bin/library/
  • Set correct export variables: (otherwise you get "fatal error: jni.h: No such file or directory")
 export JAVA_HOME=/usr/lib/jvm/java/
 export GTK_VERSION=2.0
  • Rebuild the wrapper:
 sh ./build.sh

You may get some missing library errors, like:

 fatal error: X11/extensions/XTest.h: No such file or directory
 #include <X11/extensions/XTest.h>

In this case you will need to look at the library in question and install it.

  • Copy the new .SO files across:
 cp -v ~/git/eclipse.platform.swt/bundles/org.eclipse.swt/bin/library/*.so ~/git/eclipse.platform.swt.binaries/bundles/org.eclipse.swt.gtk.linux.x86_64/
  • Building for Gtk3: repeat the previous steps except export version 3 for Gtk:
 export GTK_VERSION=3.0

This process is time consuming. To simplify it, download this build script: https://github.com/LeoUfimtsev/ldts/blob/master/pathscripts/swtjnibuild

To run it, simply do a clean (Project -> Clean) of the SWT project and then execute the script. For Gtk3, no arguments to the script are needed. To build the Gtk2 bindings, run the script with the "-2" option.

References

https://www.eclipse.org/swt/jnigen.php

The SWT codebase

Learning SWT

To learn about SWT, try out a bunch of these snippets: https://www.eclipse.org/swt/snippets/

Note, these are available in the SWT repo, search for "Snippet1.java". The org.eclipse.swt.examples project contains lots of examples to try out. There are also many many SWT tutorials online. For example, http://zetcode.com/gui/javaswt/ comes to mind.

You should learn at least:

  • Set of basic widgets (Button/Label/Table/Tree etc..)
  • Layouts (Absolute [i.e no layout]/Grid/Row/Column/FormAttach)
  • Attaching listeners

General Widget Hierarchy

Widget is the main Widget. Everything else extends Widget. The most interesting classes are Widget, Control and Composite. Most widgets fork off of these.

As such, it is useful to be aware of fields/methods in parent classes and which methods get overriden by children. In Eclipse, you can Ctrl+click on a method to see it's super implementation, or derived implementations (this is very useful).

The illustration below shows the widget hierarchy:

Swt-hiearchy.gif

About GtkHandles

Gtk Handles are basically Gtk pointers to the widgets.

When you first look at a widget, you generally first look at the handles that are defined in the widget. For example, each SWT Widget is often made up of several GtkWidgets or has pointers to GtkWidgets. In general createHandle() is a good place to start when you first look at a widget. Also inspect *Handle*() methods of the current widget and the widgets above in the hierarchy: parentHandle(), fontHandle(), childHandle(), etc. They all contain subtleties which may useful.

Handle declarations are inherited. But they are allocated and assigned at a specific widget level. For example Widget declares handle, Control declares fixedHandle but they never allocate them. These will be allocated further down the widget tree in individual widgets themselves.

For example, here is an incomplete diagram of some widgets and their handles. You may observe that widget has handle defined, and Combo has buttonHandle defined:

Handle hierarchy example.png

OS.java

All Java calls are eventually translated to GTK to do the actual drawing.

The bridge between Java and GTK is in OS.java. OS.java is a file that we write ourselves (not generated). It contains many bindings to GTK functions, but not all of them. Sometimes we have to add method signatures in there manually for new functions.

In my case, it is located here in the package path:

 /org.eclipse.swt/Eclipse SWT PI/gtk/org/eclipse/swt/internal/gtk/OS.java

Method Bindings

These are typically wrapped in a lock:

 /** @param widget cast=(GtkWidget *) */
 public static final native void _gtk_drag_dest_unset(long /*int*/ widget);
 public static final void gtk_drag_dest_unset(long /*int*/ widget) {
         lock.lock();
         try {
                 _gtk_drag_dest_unset(widget);
         } finally {
                 lock.unlock();
         }
 }

Constants and ENUMS

C constants and C Enums are delcared as plain ints. like so:

 public static final int GTK_SCROLL_STEP_UP = 6;

Note, if you need to add a C enum to OS.java, C ENUMS (Enumirations) begin at 0. Do note, that the Javadoc is parsed by the JNI parser. So be careful about what you put in there.

Static Strings translated to C-bytes

GTK uses some static strings in things like registering event handlers. We translate Java strings into C strings like so:

 public static final byte[] key_press_event = ascii("key-press-event");

GTK version

A lot of SWT code is wrapped around the if-checks that make sure code runs only on certain GTK versions. The version code is defined in OS.java like so:

 public static final boolean GTK3 = GTK_VERSION >= VERSION(3, 0, 0);


OS.Java compilation

SWT tools compiles OS.java down to a set of files like os.c. Be attentive, there are two sets of library files like os_custom.c. This is because one set is the source, the second is copied over during compilation.

Source folder is here (this is where you should make changes):

 ~/git/eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT PI/gtk/library/os_custom.c

Destination/binary/compiled folder is here:

 ~/git/eclipse.platform.swt/bundles/org.eclipse.swt/bin/library/os_custom.c

It is important to understand the difference because later you will be making changes in the source folder, but link the debugger to the source code in the destination/bin folder. Do note, inside the source folder, some of the files we adjust by hand and some of these are generated. The content of ../library/.. is as following:

os.c

 This file is automatically generated by SWT Tools. It contains native bindings.

os.h

 This file we adjust manually. It contains special signatures.

os_stats.*

 These are auto-generated.

os_custom.h

 This file we adjust manually. We add new function signatures here when we add a new method to OS.java.

os_custom.c

 This file we adjust manually. This contains our custom code, such as the SWTFixed container.

When SWT Tools re-generates os.h os.c etc., they may appear in your git staging area. When submitting a patch, include these in the submission.

SWT Code style notes

Javadocs

No platform dependent info: no technical details that are platform-specific go into Javadocs. (e.g no GTK specific items). putting them in regular non-Javadoc (green) comments is OK.

Method naming

GTK functions: any GTK-specific functionality should be gtk_function_name. Even if it doesn't match one-to-one to a gtk function. (do try to avoid conflicts thou).

Any other naming should be general enough to be translated to other platforms.

Method access modifiers

Methods should in general not have modifiers unless private/public.

 void myMethod()...

Avoid 'protected' unless you're sub-classing things.

SWT Bug naming conventions

Cheese

This refers to garbled text or messed up pixels.

DnD

Usually used for Drag and Drop.

Win32/Cocoa/Gtk

These you will see as prefixes in bug-titles. They stand for the different platforms that SWT uses for the Eclipse UI. On Windows it's Win32, on Mac/OSX it's Cocoa, and on Linux it's GTK.

Adding custom functions to OS.java

This flow chart describes the process of adding a new function to OS.java very well: Os custom flowchart.png

Adding new functions

New functions are introduced in GTK3 and old functions are deprecated. In these situations we need to manually add these method signatures to OS.java and os_custom.h.

Dynamic vs. static functions

Dynamic functions are not build during compile time. They are only called at run time. This allows us to have GTK3 functions in a GTK2 build or run deprecated functions only in GTK2 (or some specific gtk* version range). Dynamic functions have an annotation:

 @method flag=dynamic

Re-building SO-files

After you add new functions to OS.java & os.h, you will need to rebuild the SO file for GTK2 & GTK3.

Dynamic methods and os_custom.h

Before adding a new function to OS.java, you should understand dynamic functions.

If you inspect OS.java and look at the Javadoc of some of the functions, you will notice a flag like this:

 @method flags=dynamic

This means the command is not compiled, but called dynamically on the fly (runtime). This is useful for functions that are specific to certain versions of GTK. E.g some functions were only introduced in GTK3, as such those won't compile on a GTK2 build. As such you make those dynamic. Similarly, some GTK2 functions are deprecated in GTK3 and so that we only use them in GTK2, thus we make them dynamic.

Note: not all functions have to be dynamic. You should only make them dynamic if there is a need for it. I.e, in general you should only make functions dynamic if they have to be dynamic; this is because if errors do exist, this post-pones them from compile time to run time.

Determine if function should be dynamic

It is important to thoroughly check if the function that you are about to add is specific to GTK2, or GTK3 or can be included in both. Be attentive, sometimes there are bugs in the documentation, i.e it might be missing a 'since 3.xyz' flag. The safest way to ensure functionality is to check both the latest GTK3 and GTK2 documentation and read up about the function in both places.

To do that, is to find the function, then change the '3' to a '2' in the URL, for example: https://developer.gnome.org/gtk3/stable/GtkWidget.htm and https://developer.gnome.org/gtk2/stable/GtkWidget.htm

For example, gtk_widget_set_halign() is defined in the GTK3 documentation and there is no 'since 3.0' flag. However, upon checking of GtkWidget in GTK2, I found that the function doesn't exist there. Sometimes the function is OK to use in the current stable build, but got deprecated in the most recent unstable build. So check unstable documentation prior to adding the function also. (replace stable with 'unstable' in the URL).

Another indication of functions not being present in certain GTK versions is that you might get an 'implicitly defined function' in the build.sh output.

Steps to make a function dynamic

Add the @method flag=dynamic to the Javadoc of the function, and add the signature to os_custom.h. (i.e look at the other signatures, copy & adjust).

Be careful, there is a suffix 'LIB' at the of the function:

 #define gtk_widget_get_preferred_size_LIB LIB_GTK        ## Notice the suffix "_LIB"

The 2nd part of the Define 'LIB_GTK' is a pointer to which library the function comes from. In this case preferred size comes from LIB_GTK. But this can be LIB_GDK or other libraries. Check the GTK documentation to find out where the function comes from.

As usual, after modifying any of the OS files, the SOs need to be rebuilt. Be sure to include 32 bit casting and enable SWT Tools' "32/64 bit checking". SWT Tools also generates JNI bindings (i.e. os.c, os_stat.c, etc.) for you automatically. To force these bindings to be rebuilt, clean your project.

Adding custom C enums to OS.java

C Enums are enumerations. I.e, {Red,Green,Blue} is turned into {0,1,2}.

C enums don't map onto Java's enums. Instead, to add an enum like GtkAlign to OS.java, declare some static ints like:

 /**
  * ## Enums, extracted from OS.java (I once had to add this one in).
  */
 /** GtkAlign enum */
 public static final int GTK_ALIGN_FILL = 0;  //Enums start at 0.
 public static final int GTK_ALIGN_START = 1;
 public static final int GTK_ALIGN_END = 2;
 public static final int GTK_ALIGN_CENTER = 3;
 public static final int GTK_ALIGN_BASELINE = 4;

And when you declare a function, delcare the java-doc paramater cast like this:

 @param gtkalign cast=(GtkAlign)    // note (GtkAlign) with no pointer, not (GtkAlign *)

This will allow the native call to understand that the paramater is an enum.

Appendix: Special custom bindings

In some rare situations you might have a function that you can't easily make dynamic. E.g an overloaded function that has structs that are supported only in Gtk2/Gtk3. In java you can overload a function, but in C you cannot.

In such situations, we need to inspect the generated os.c, find the "NO__.." line that is generated by SW Tools and put it into os.h.

Example: g_object_set() Suppose you have:

 _g_object_set(long /*int*/ object, byte[] first_property_name, GdkRGBA data, long /*int*/ terminator);       ### GdkRGBA is specific to gtk3.

Add the method signature to OS.java. Clean the project and attempt a build. You will get a build error about GdkRGBA paramater in g_object_set(). This is because GdkRGBA only exists in GTK3.4+.

Now search os.c for "NO__ …. g object set ", you will find something like:

 NO__1g_1object_1set__J_3BLorg_eclipse_swt_internal_gtk_GdkRGBA_2J 

Then in os.h, near ~ #define NOGdkRGBA you would add:

 #define NO__1g_1object_1set__J_3BLorg_eclipse_swt_internal_gtk_GdkRGBA_2J

Meaning: (not very interesting as this is SWT generated, but FYI:) J - long I - int 3B - byte[] NOTE: if there is a 'J' - long in the signature, you need to add a 2nd line with 'I' ints, like:

 #define NO__1g_1object_1set__I_3BLorg_eclipse_swt_internal_gtk_GdkRGBA_2I   //J*->I
 #define NO__1g_1object_1set__J_3BLorg_eclipse_swt_internal_gtk_GdkRGBA_2J

Alexander Kurtakov taught me this business. If you get stuck here, consider getting in touch with him for help.

References

https://www.eclipse.org/swt/jnigen.php https://www.eclipse.org/swt/jnigen_metadata.php http://homepage.cs.uiowa.edu/~slonnegr/wpj/JNI.pdf

SWT Fixed Container

SWTFixed is custom C code that we include in SWT. It is a container that allows us to place SWT Widgets with absolute positioning so that subsequent widgets are drawn beneath each other. (In GtkFixed container, subsequent widgets are drawn on top of previous once). This is achieved by using the gtk_widget_show_unraised() method, (show widget, but do not raise it up).

As such, the swt_fixed_for_all() method that traverses the code is a bit different than standard for_all() methods.

SWTFixed was introduced in SWT during the GTK2 to GTK3 migration, because the old GtkFixed container was removed in GTK3.

SWTFixed is defined in os_custom.h and os_custom.c. In my case they are here:

 ~/git/eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT PI/gtk/library/os_custom.c

Every widget is based on SWTFixed

If you inspect a widget, in almost every createHandle() method, you will see the creation and allocation of SWTFixed like so:

 fixedHandle = OS.g_object_new (display.gtk_fixed_get_type (), 0);
 OS.gtk_widget_set_has_window (fixedHandle, true);

This means that SWT is creating a new instance of the SWTFixed container. Normally it then assigns something to the handle variable puts the widgets inside it.

Usually in GTK you create a drawing surface (GdkWindow) [note the 'd'] and draw one or several widgets inside it. In SWT, we create a new drawing surface (GdkWindow) for every single widget. This is very ineffective but gives SWT more control about drawing order and permits easier implementation of overlapping widgets. At this point it might be beneficial to understand that a GdkWindow is a drawing surface, where as a GtkWindow [note 't vs d' difference] is a shell with decorations like 'X', '-' and it interacts with the X drawing system. More will be discussed in the GTK sections that follow.

Technical C details

You might want to read a bit on how to implement a custom widget in GTK. Then SWTFixed will be much easier to understand. It's mostly code copied from other generic GTK containers with a few tweaks here and there.

Specifically:

  • SWTFixed extends GtkContainer, i.e it inherits all its functions. This can be observed by the SWTFixedPrivate struct, it has a reference to GtkContainer meaning that the GtkContainer widget is its parent
  • Supports multiple children because the child object is a list.
  • It overrides some function, this can be observed in the init() function, which assigns functions to pointers. I.e.:
 container_class->forall = swt_fixed_forall;

SWT and GTK versions

With SWT, the version of GTK that you're running on can make a big difference in how your snippet will behave. This is especially true for all things CSS related because there are many changes in that area.

It's not just the difference between GTK2 & GTK3, but keep an eye on the differences between:

  • GTK3.8: RHEL 7 and Fedora 19
  • GTK3.10: CSS theming introduced, lots of things break between GTK3.8 and GTK3.10 because of this
  • GTK3.12: nothing super exciting
  • GTK3.14: Fedora 21, RHEL 7.2
  • GTK3.16: Fedora 22, removal of stock icons, gtk_widget_override_* functions become deprecated
  • GTK3.18: Fedora 23, re-skin of File Chooser, CSS nodes.
  • GTK3.20: Fedora 24, complete overhaul of CSS machinery to use CSS nodes. Old style selectors won't work. Changes to GtkInspector.

Because of the faster pace at which the GTK development cycle works, it is imperative to be able to test on different versions of GTK (within reason). Usually testing 2-3 versions behind is useful for Fedora. Try to test on GTK3.8 as RHEL customers use this and require an especially stable platform. GTK2 is worth testing on to make sure no regressions are introduced (as SWT currently supports GTK2), but we are not fixing any new GTK2 bugs.

To find out which exact versions are currently supported by SWT, inspect GTK's Display.java:

http://git.eclipse.org/c/platform/eclipse.platform.swt.git/tree/bundles/org.eclipse.swt/Eclipse%20SWT/gtk/org/eclipse/swt/widgets/Display.java

And search for code like this:

 /* GTK Version */
 static final int GTK3_MAJOR = 3;
 static final int GTK3_MINOR = 0;
 static final int GTK3_MICRO = 0;
 static final int GTK2_MAJOR = 2;
 static final int GTK2_MINOR = 18;
 static final int GTK2_MICRO = 0;

This means GTK3.0.0 and GTK2.18.0 onward are supported.

Once in a while, you will come across bugs where the version is bumped. Keep an eye on this by following platform-swt-inbox@eclipse.org in the Eclipse Bugzilla. For example:

 https://bugs.eclipse.org/bugs/show_bug.cgi?id=446454

Launching SWT applications on GTK2 or GTK3

You often want to test if something occurs only on GTK3 or if it occurs on GTK2 also. To do so, launch a snippet. Close it and then edit the run configuration. Under environmental variables, add:

 SWT_GTK3 with a value of 1 for GTK3, 0 for GTK2.

This will launch the SWT application using the latest GTK3/2 installed on your system. Similarly, you can set your system Eclipse to launch with GTK3 or GTK2 by modifying the eclipse.ini file to add the following section:

 --launcher.GTK_version
 3                              ### 2 for GTK2, 3 for GTK3.

To find out what version of GTK3 is installed on your system, run the following command (pkg-config must be installed):

 pkg-config --modversion gtk+-3.0

Additionally, you can run the following command on Fedora/RHEL/CentOS:

 rpm -q gtk3

You can find the GTK version programmatically in SWT as well:

 //Print Gtk version.
 System.out.println("GTK Version: " + OS.gtk_major_version() + "."
   + OS.gtk_minor_version() + "." + OS.gtk_micro_version());
 
 //I have a function in my set of test-widgets that get's me the gtk version.
 public static String getGtkVersion () {
       return OS.gtk_major_version() + "." + OS.gtk_minor_version() + "." + OS.gtk_micro_version();
 }
 
 //Normally I set the shell-title to the Gtk version:
 shell.setText (ShellTest.getGtkVersion ());

Finding what version of GTK Eclipse is running on

Leo Ufimstev wrote an excellent blog post on this subject: https://coffeeorientedprogramming.wordpress.com/2014/09/29/how-to-compile-various-gtk3-versions-and-run-eclipse-apps-with-those/

GTK Versions on Fedora/Red Hat

For more information on this, please see: determining the version of GTK3 on Fedora/RHEL

Your snippet might work well on GTK3.14, but might will fail on GTK3.8. Or someone's code will only work/fail only on some specific version of GTK. You need to be able to run snippets on specific versions of GTK.

You could of course set up 5 VM's with various Fedora/RHEL versions, but it would be tedious to test things. This is especially true for CSS & style related changes. To remedy this problem you can compile different versions of GTK locally and tell SWT to use those versions. This guide will show you how to do so. Simply use the LD_LIBRARY_PATH environment variable and point it to your .libs folder that you got from compilation. For example:

 LD_LIBRARY_PATH
 /home/ericwill/src/gtk_versions/3-14/gtk/gtk/.libs

Note: GTK releases are as follows. Even numbered releases are stable, odd numbered releases are development releases. Therefore it's unnecessary to test on versions like GTK3.13, 3.15, etc. Instead test on GTK3.8, 3.10, 3.14, 3.16, etc. You can compile any version of GTK3 until GTK3.2. It is not necessary to compile versions of GTK2 as we only use one version of GTK2, and behavior across GTK2 versions is pretty standard.

About GTK

Often you will run into a situation where you have to write native GTK code to see if the issue is in GTK or in SWT. You should become comfortable writing and compiling GTK3 (and maybe GTK2) native code.

Brief overview of GTK

GTK vs. GDK

It's not all "Gtk". Some functions start with gDk and some with gTk. Be attentive to the prefix and seek out the relevant documentation. In general, Gtk is build on top of the underlying Gdk. For example for Drag and drop, there are GDK and GTK functions like:

 gtk_drag_cancel()
 gdk_drag_abort()

Both are different from one another: https://developer.gnome.org/gtk3/stable/gtk3-Drag-and-Drop.html https://developer.gnome.org/gdk3/stable/gdk3-Drag-and-Drop.html

General structure of GTK

In fact, GTK is a composition of multiple libraries. But in most cases, GTK/GDK/GLib is all you need to know unless you're working on some drawing related issue.

 //GTK composition:
 GKT+
 |-> X11     (Xlib)     ## Window manager
 |-> Glib ()
     |-> Glib ()
     |-> GObject ()     ## Object-oriented framework
     |-> GModule ()
     |-> GThread ()
     |-> GIO ()
 |-> Cairo   ()         ## 2-D Vector renderer 
 |-> GDK ()             ## wrapper around low-lvl graphics. (fonts/dnd,cursors)
 
 |-> GdkPixbuf ()       ## image manipulation.
 |-> Pango ()           ## Text/Font
 |-> ATK ()             ## Accessibility toolkit.
 
 //Structural overview
 +------------------------------- ----------+
 |             Your Application             |
 +------------------------------------------+
 |                 GtkAda                   |
 |              +-----------------+         |
 |              |      GTK        |         <<< Useful to know.
 |         +----+-----------------+----+    |
 |         |           GDK             |     <<< Useful to know.
 |    +----+------+         +----------+----+
 |    |   Pango   |         |     Cairo     |
 +----+-----------+----+----+---------------+
 |        GLIB         |   X-Window / Win32  |
 +-------- ^ -----------+--------------------+
           |
          Glib has some useful datastructures, e.g lists/hash tables.
 
 //From GTK to your app:
 Xlib <-> GDK <-> GTK <-> Your App ## GDK is intermediate

Learning GTK

Good places to get you going are:

  • The GTK2 book: the only (decent) book on GTK at the time of writing covers GTK2. But it's good to learn about GTK2 and in parallel look at how things changed in GTK3. GTK2 and GTK3 are relativley similar. More info here: http://www.gtkbook.com/ It's good to read the book and compare the functions/structs to GTK3. This way you learn both frameworks.
  • There is also a very good book written by Red Hat Labs: "GTK+ / Gnome Application Development, Havoc Pennington, Red Hat Advanced Development Labs". It is the only book I could find that had good high-level theory on GDK development and it has some nuggets like implementing a custom widget (which is useful to understand SwtFixed container).
  • There are lots of little papers scattered around the web also. I google around for those.

GTK API documentation

GTK2 & GTK3 documentation: there is (GTK3|GTK2) && (Stable|Unstable) documentation, to switch between them change 2 -> 3, stable -> unstable. E.g:

I usually Google with "GTK" and "ref" in the prefix. This usually gets me to the API:

 gtk<Version> ref <Key word>
 
 e.g
 gtk3 ref gtk_combo_box_text
 gtk2 ref gtk_combo_box_text

Note about the unstable API:

You should consider browsing unstable API more often than stable API. Often you will find that some functions get deprecated in latest versions or new functions are added to add missing functionality. Or simply the documentation changes. The general rule of thumb is that before adding new method to OS.java, double check the unstable documentation for that function first.

Getting help with GTK

  • GTK+ IRC channel: Folks are very helpful here. I often got responses very quickly. Mostly good for quick little bits and general wisdom.
  • GTK+ bugzilla: If you think you have come across a bug, or need some official statment from GTK folks about some functionality (e.g if something doesn't work in SWT, have a link to a gtk bug that explains things). Posting a bug to the GTK bugzilla is the way to go. E.g: https://bugzilla.gnome.org/show_bug.cgi?id=747798
  • Mailing lists: I didn't get many responses when I asked complex questions, but for small & straight forward stuff, people respond quite well: See: http://www.gtk.org/mailing-lists.php
  • Stack Overflow: For your broken snippets. Tag things with gtk+ http://stackoverflow.com/
  • See: http://www.gtk.org/development.php

GTK source code

You should check out the GTK repository. Often you will look through the GTK source code to find things that are not in their documentation. Usually I look for the macros that cast things e.g GTK_CONTAINER(container) or I look at *.h files to see how widgets are made up.

GtkInspector

GtkInspector is a good friend when it comes to troubleshooting styles/positioning and functionality of widgets. It can provide information about running GTK Applications. Note, this includes Eclipse or a SWT snippet when they run on Gtk3.14 or above.

Things it can do:

  • Display widget hierarchy
  • Live tweaking of properties (including CSS styles)
  • Point and shoot widget identification
  • Allow traversal of the widget hierarchy (i.e., clicking on an SwtFixed container and then browsing its contents)
  • CSS theming on the fly
  • Memory, allocation, mapping, and other lower level information

Opening GtkInspector

When in a GTK app, press the keybinding for the GtkInspector: Ctrl + Shift + I. Note, to enable the GtkInspector a GSettings setting must be enabled:

 gsettings set org.gtk.Settings.Debug enable-inspector-keybinding true

Limitations

GtkInspector launched at the start of an application sometimes does not show new widgets in the hierarchy unless you close and re-open GtkInspector. Furthermore, it does not support re-parenting: for example if a widget that makes calls to gtk_widget_reparent() is run, GtkInspector will not show the updated hierarchy. If hierarchy matters/is crucial, check points/memory addresses.

References

Upgrade Ubuntu's GTK to use gtkInspector: http://www.webupd8.org/2014/10/how-to-install-gnome-314-in-ubuntu.html

Leo's blog post on it: https://coffeeorientedprogramming.wordpress.com/2014/10/27/how-to-tell-if-you-are-running-eclipse-on-gtk2-or-on-gtk3/comment-page-1/#comment-8

Matthias Clasen's blog post: http://blogs.gnome.org/mclasen/2014/11/23/gtk-inspector-update/ https://wiki.gnome.org/Projects/GTK+/Inspector

C/C++ Development in Eclipse

Eclipse has a plugin/perspective called "C/C++ Development Tools" or CDT. This is useful for reading the GTK code base as well as writing small native GTK snippets.

Getting started

If you are using Fedora Eclipse you can install the CDT using dnf:

 sudo dnf install eclispe-cdt

Alternatively if you are using upstream Eclipse, you can get it from the CDT update site: https://eclipse.org/cdt/downloads.php

To get a feel for using CDT:

Different types of C projects

When you create a new C project, you will have an option of several project types. The main types are:

  • GNU Autotools: this is often used by large open source projects, i.e. GTK. It ties making of projects together with developer tools like valgrind.
  • Executable: this is a basic project where the make file is managed for you. This is good if you just want to write some C code and try it out.
  • Makefile Project: this is for when you manage your own makefile. This is useful for existing projects that have make files that you need to manage yourself, or for when you want to learn about makefiles. To enable debug in makefile projects, you need to add the debug flag and remove optimizations:
 -g -O0

Useful tips for navigating C code using Eclipse/CDT

You should try all of the above:

  • Switch between .h and .c files: you acn press Ctrl+Tab to switch between source code and header units.
  • Open call hierarchy: I remap this to F1. List all the functions that call this method. Also works on fields of a struct, show all places that reference this variable.
  • Quick outline: (ctrl+o) See a list of all functions. Search them (regex supported).
  • Open resource: navigate menu > open resource or Ctrl+Shift+r. This is very useful to find or 'jump' to a file. Supports regex.
  • Refactor: (shift+alt+r) Rename variables and functions.
  • Build & run: you can configure a build & run in one hotkey. You should create a run configuration (see help->help content->C/C++Development ->getting started > Creating a simple application). Enable 'auto-build'. Now tie a hotkey to "run-last-launched" (F12 in my case, but maybe F11 in yours).
  • Open element: (Ctrl+Shift + t) useful for finding functions/structs/unions/enums in the source code base.

Import GTK source code into Eclipse for browsing

You can pull GTK sources and tie them into your Eclipse, so that you can navigate/read the source code easier. I then use the GTK source code as a way of reading GTK API. Compared to the web-documentation, reading the source code allows you to quickly jump to struct definitions and see examples of how/where functions are called via call-hierachy.

You also see how certain objects 'relate' to each other, which you sometimes don't see in the web-documentation. You will often find that many functions are just wrappers around other functions. The most frequent use-case is when I write a GTK snippet, I can just jump to the function definition and read the documentation without plowing through the web-documents.

Git repositories to check out for GTK development

GTK is made up of several libraries and you need to pull all of them onto your system.

 cd ~/git
 
 #GTK (including GDK)
 git clone https://github.com/GNOME/gtk
 
 #Glib
 git clone https://github.com/GNOME/glib.git
   
 #gdk-pixbuf
 git clone https://github.com/dieterv/gdk-pixbuf.git
 
 #Cairo drawing library:
 git clone git://anongit.freedesktop.org/git/cairo.git
 git clone git://anongit.freedesktop.org/git/pixman.git

Import sources into Eclipse as projects

Importing projects from git into Eclipse

  • You should have the repos checked out: (gtk+|glib|gdk-pixbuf|pixman|cairo).
  • Right click on each git repository and import from it.
  • Import it as "New C project" (and not exiting project).Project type "GNU Autotools" -> Empty Project" uncheck 'Use default location' and select location in your git hub. (root of the .git)

Referencing projects

Referencing projects allows Eclipse to know that projects are related. Normally, triggering to build one project triggers a build of other projects. It also get the C indexer to read symbols properly.

  • Go to the imported 'gtk+' project.
  • Open 'project properties' -> C/C++ General -> Paths and Symbols -> References
  • Check: glib && gtk-pixbuf && cairo && pixman
  • Click on OK.

Rebuild the index

  • In the project explorer, right click on the 'gtk' project -> index -> rebuild.
  • Now all errors should be gone, except maybe one like:
 cannot find install-sh, install.sh, or shtool in build-aux "."/build-aux
  • To fix, run reconfigure from repo, autotools will rebuild the project bits

References

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