GTK BoF at Guadec

As every year, we had a GTK BoF at Guadec in Thessaloniki. This year, we had a pretty good turnout — everybody was interested in GTK4 plans.

But since Emmanuele was busy in the morning, we started the discussion with some other topics.

GLib

We collected a few suggestions for useful GLib additions from the room.

  • API for OS information (basically, the data that is in /etc/os-release). This seemed uncontrolversial; Robert is going to implement it
  • An ordered map. This is implemented ad-hoc in many places by combining a hash table with a list or array.  There seemed to be agreement that it would be worthwhile to provide this in GLib, if somebody does the work to propose an API

The discussion of ordered maps also touched on generic container interfaces; Philipp described how that could be done, see details here.

Still on the topic of containers, Alex described a problem with transfer annotations. We discussed various ideas, but there may not be a perfect solution.

Matthias pointed out that there is still some Unicode data in Pango. We briefly discussed how nice it would be to have an agreed-on, mmappable binary format for Unicode data, so that everybody could share it. Short of that, moving the last bits of data to GLib was uncontroversial.

Dark mode

Since the “dark mode” BoF joined us, we switched to discussing dark mode next. There was a more discussion of this topic in the vendor theme BoF the next day; the GTK discussion focused on technical details of how to implement dark mode.

There are various options:

  • Add extra metadata to theme index files to mark themes as dark
  • Add a “dark-theme-name” setting and treat dark and light themes as independent
  • Keep the existing convention of appending “-dark” to theme names to find the dark variant of a theme

The pragmatic solution of keeping the existing convention seemed to have support in the room. Matthias started exploring some application support APIs here.

GTK

Eventually we swiched to talking about the state of and progress towards GTK4. The high-level summary is that there is still a list of  features that need to be completed for GTK4:

  • A scalable list view that recycles row widgets. This includes a broader switch to using list models in more places. To make it complete, it should also include a grid view using the technologies. Benjamin is working on this
  • Infrastructure and APIs for animations. This will be similar to the way animations work in CSS, and part of the work is to port not just our existing CSS animation support, but also stack switching animations, the revealer, progress bars and spinners to the new framework. Emmanuele is working on this.
  • Complete the menu/popover rework. Some people tried the new popover menubar. The feedback was that we should probably go back to nesting submenus, at least for menubars, and push forward with dropping menus, since some of the ways in which menus are special (such as keep-up triangles, scrolling) are hard to keep working (or keep working well). Matthias is getting back to working on this after Guadec.
  • Shortcuts – replace mnemonics, accelerators, and key bindings with event controllers. There is a fairly complete branch with code and APIs that several people have worked on; help with reviewing and testing it would be appreciated.
  • The new Drag-and-Drop API needs to be completed.

The good news is that this list is fairly short and has names next to most items. The bad news is that each item is a considerable amount of work. Therefore, it is not a good idea to promise a tight timeline towards the 4.0 release before we have all of them merged. Thus, the following is tentative, but (we hope) somewhat realistic:

  • another GTK 3.9x snapshot before the end of this year
  • a feature-complete 3.99 release around the same time as GNOME 3.36 in spring 2020
  • a 4.0 release around the same time as GNOME 3.38 in fall  2020

Inevitably, we also discussed other things that would be nice to have. None of these are on the GTK4 roadmap; but if somebody shows up to do the work, they can happen:

  • A “widget repository” or “hig” library in order to not overload GTK with too specific or experimental widgets
  • A “UI designer” widget. This could live in a separate library as well
  • Better support for split headerbars and state transitions

We also discussed things outside GTK proper that will keep applications from porting to GTK4. This includes commonly used libraries such as GtkSourceView, vte and webkitgtk, which all will need GTK4 ports before applications that depend on them can be ported. Some of this work is already underway; but any help in this area is appreciated!

Another potential blocker for GTK4 porting is platform support. The GL renderer works well on Linux; the Vulkan renderer needs some fixups. On Windows we currently use cairo fallback, which may be good enough for 4.0. Alternatively, we could merge existing work for using the GL renderer with ANGLE. The situation is less pleasant on OS X, where we don’t have a working backend; if you want to help us here, the first still would be to adapt the GDK backend to changes in GDK.

Hacking time

In the afternoon, the room drifted from discussion to hacking, and various GTK-related works-in-progress could be spotted on peoples laptops: work to speed up GtkBuilder template loading, nested popover menus, a half-finished GtkSourceView port.

You will hopefully see these (and others) in GTK master soon.

GTK 3.96.0

This week, we released GTK 3.96.0. Again, it has been a while since the last release, so it is worth summarizing whats new in this release. There is really too much here to cover it all, so this post will only highlight the most important changes.

This release is another milestone on our way towards GTK 4. And while there are still some unfinished things, this release is much closer to we hope to achieve with GTK 4.

GSK

GSK has seen a number of bug fixes and new tests that are made much easier using a new debug tool, gtk4-node-editor. It can load and display serialized render node trees, such as this one that was saved from the GTK inspector, and compare the output of different renderers.

The 3D transformation support has been brought up to the level where we can do animated transitions like the cube spin below.

GDK

The trend to move toward Wayland inspired APIs has continued, with more X11-only apis being moved to the X11 backend or just removed. Use of child surfaces and global coordinates has been greatly reduced, but this work remains incomplete.

The refactoring of Drag-and-Drop has also continued, with the introduction of GdkDrag and GdkDrop objects. The GTK part of this refactoring is still incomplete.

Events have been simplified and are now used just for input. Other event have been replaced by signals and properties on GdkSurface. In detail, expose events have been replaced by the ::render signal, configure events have been replaced by the ::size-changed signal. Map events have been replaced by the :mapped property, and gdk_event_handler_set() has been replaced by the ::event signal.

The Wayland backend has gained support for the Settings portal for GtkSettings, and uses the text-input-unstable-v3 protocol for its input method support.

GTK

Widgets

One big change for custom widgets is the introduction of GtkLayoutManager, which is a new delegate object that takes over size allocation. Layout managers can optionally use layout children for holding layout properties. This replaces the layout-related child properties in GTK containers such as GtkBox or GtkGrid.

A number of layout managers are available:

  • GtkBinLayout, for simple single-child containers
  • GtkBoxLayout, for children that are arranged linearly
  • GtkGridLayout, for children that are arranged in a grid
  • GtkFixedLayout, for freely positioned and transformed children
  • GtkCustomLayout, as a quick way to turn traditional measure and size_allocate vfuncs into a layout manager

More layout manager implementations will appear in the future. Most prominently, work is underway on a constraints-based layout manager.

GtkAssistant, GtkStack and GtkNotebook have publicly
accessible page objects for their children. The page objects
are also exposed via a list model. They non-layout related child properties of these containers have been converted into regular properties on these page objects.

Since all existing child properties have been converted to regular properties, moved to layout properties or moved to such page objects, support for child properties has been dropped from GtkContainer.

The core GtkEntry functionality has been moved into a new GtkText widget, which also implements an expanded GtkEditable interface. All existing entry subclasses in GTK have been turned into GtkEditable implementations wrapping a GtkText widget. This also includes a new GtkPasswordEntry.

Other Changes

GTK widgets can transform their children using projective linear
transformations. This functionality is available in CSS and
as a GskTransform argument to gtk_widget_allocate. GtkFixed is
the first container that exposes this functionality. For further examples,
see the swing transition of GtkRevealer, the rotate transitions
of GtkStack or the Fixed Layout example in gtk4-demo.

A number of list models have been introduced, for internal use
and as public API: GtkMapListModel, GtkSliceListModel, GtkSortListModel, GtkSelectionModel, GtkSingleSelection. These will become more widely used when we introduce a list model-based GtkListView.

GtkBuilder can specify object-valued properties inline, instead of referring to them by ID, and the simplify command of gtk4-builder-tool has gained an option to automatically convert GTK 3 UI definition files to GTK 4.

Coming soon

For more information on the things that are still still coming for GTK 4, find us on Discourse, IRC, or look here.

Entries in GTK 4

One of the larger refactorings that recently landed in GTK master is re-doing the entry hierarchy. This post is summarizing what has changed, and why we think things are better this way.

Entries in GTK 3

Lets start by looking at how things are in GTK 3.

GtkEntry is the basic class here. It implements the GtkEditable interface. GtkSpinButton is a subclass of GtkEntry. Over the years, more things were added. GtkEntry gained support for entry completion, and for embedding icons, and for displaying progress. And we added another subclass, GtkSearchEntry.

Some problems with this approach are immediately apparent. gtkentry.c is more than 11100 lines of code. It it not only very hard to add more features to this big codebase, it is also hard to subclass it – and that is the only way to create your own entries, since all the single-line text editing functionality is inside GtkEntry.

The GtkEditable interface is really old – it has been around since before GTK 2. Unfortunately, it has not really been successful as an interface – GtkEntry is the only  implementation, and it uses the interface functions internally in a confusing way.

Entries in GTK 4

Now lets look at how things are looking in GTK master.

The first thing we’ve done is to move the core text editing functionality of GtkEntry into a new widget called GtkText. This is basically an entry minus all the extras, like icons, completion and progress.

We’ve made the GtkEditable interface more useful, by adding some more common functionality (like width-chars and max-width-chars) to it, and made GtkText implement it. We also added helper APIs to make it easy to delegate a GtkEditable implementation to another object.

The ‘complex’ entry widgets (GtkEntry, GtkSpinButton, GtkSearchEntry) are now all composite widgets, which contain a GtkText child, and delegate their GtkEditable implementation to this child.

Finally, we added a new GtkPasswordEntry widget, which takes over the corresponding functionality that GtkEntry used to have, such as showing a Caps Lock warning

or letting the user peek at the content.

Why is this better?

One of the main goals of this refactoring was to make it easier to create custom entry widgets outside GTK.

In the past, this required subclassing GtkEntry, and navigating a complex maze of vfuncs to override. Now, you can just add a GtkText widget, delegate your GtkEditable implementation to it, and have a functional entry widget with very little effort.

And you have a lot of flexibility in adding fancy things around the GtkText component. As an example, we’ve added a tagged entry to gtk4-demo that can now be implemented easily outside GTK itself.

Will this affect you when porting from GTK 3?

There are a few possible gotcha’s to keep in mind while porting code to this new style of doing entries.

GtkSearchEntry and GtkSpinButton are no longer derived from GtkEntry. If you see runtime warnings about casting from one of these classes to GtkEntry, you most likely need to switch to using GtkEditable APIs.

GtkEntry and other complex entry widgets are no longer focusable – the focus goes to the contained GtkText instead. But gtk_widget_grab_focus() will still work, and move the focus the right place. It is unlikely that you are affected by this.

The Caps Lock warning functionality has been removed from GtkEntry. If you were using a GtkEntry with visibility==FALSE for passwords, you should just switch to GtkPasswordEntry.

If you are using a GtkEntry for basic editing functionality and don’t need any of the extra entry functionality, you should consider using a GtkText instead.

Theme changes, revisited

A quick update on last weeks post about theme changes:

We’ve made a 3.24.4 release, to fix up a few oversights in 3.24.3. This release does not include the new theme yet, we will push that to the next release.

We’ve also made another NewAdwaita tarball, which includes refinements based on some of the suggestions we received since last week.

Try it out, and tell us about it!

Theme changes in GTK 3

Adwaita has been the default GTK+ theme for quite a while now (on all platforms). It has served us well, but Adwaita hasn’t seen major updates in some time, and there is a desire to give it a refresh.

Updating Adwaita is a challenge, since most GTK applications are using the stable 3.x series, and some of them include Adwaita-compatible theming for their own custom widgets. Given the stable nature of this release series, we don’t want to cause theme compatibility issues for applications. At the same time, 3.x is the main GTK version in use today, and we want to ensure that GTK applications don’t feel stale or old fashioned.

A trial

A number of approaches to this problem have been considered and discussed. Out of these, a tentative plan has been put forward to trial a limited set of theme changes, with the possibility of including them in a future GTK 3 release.

Our hope is that, due to the limited nature of the theme changes, they shouldn’t cause issues for applications. However, we don’t want to put our faith in hope alone. Therefore, the next three weeks are being designated as a testing and consultation period, and if things go well, we hope to merge the theme into the GTK 3.24.4 release.

It should be emphasised that these changes are confined to Adwaita itself. GTK’s CSS selectors and classes have not been changed since GTK 3.22, and the changes in Adwaita won’t impact other GTK themes.

The Adwaita updated theme is being made available as a separate tarball in parallel with the GTK 3.24.3 release, and can be downloaded here. GTK application developers are invited to try 3.24.3 along with the new version of Adwaita, and report any issues that they encounter. The GTK team and Adwaita authors will also be conducting their own tests. Details of how to test the new theme in various ways are described here.

We are hoping to strike a balance between GTK’s stability promises on the one hand, and the desire to provide up-to-date applications on the other. It is a delicate balance to get right and we are keen to engage with GTK users as part of this process!

Theme changes

The rest of this post summarises which changes are have been made to the theme. This will hopefully demonstrate the limited extent of these changes. It will also help developers know what to look for when testing.

Colors

Many of the Adwaita colors have been very slightly tweaked. The new colors are more vivid than the previous versions, and so give Adwaita more energy and vibrancy. The new colors also form part of a more extensive palette, which is being used for application icons. These colours can also be used in custom application styling.

The color changes are subtle, so any compatibility issues between the new and the old versions should not be serious. Blue is still blue (just a slightly different shade!) Red is still red. Visually, the dark and light versions of the theme remain largely the same.

Adwaita’s dark variant, showing the slight color changes between old (left) and new (right).

Note that the red of the button has been toned down a bit in the dark theme.

Header bars and buttons

Most widgets have not been specifically changed in the updated version of Adwaita. However, two places where there are widget-specific changes are header bars and buttons. In both cases, an effort has been made to be lighter and more elegant.

Buttons have had their solid borders replaced with shadows. Their background is also flatter and their corners are more rounded. Their shape has also been changed very slightly.

Header bars have been updated to complement the button changes. This has primarily been done by darkening their background, in order to give buttons sufficient contrast. The contrast between header bars’ focused and unfocused states has also been increased. This makes it easier for users to identify the focused window.

At first glance, these changes are some of the most significant, but they are achieved with some quite minor code changes.

The header bar in GNOME’s Calendar app (old version on top, new version on the bottom):

Switches

Aside from header bars and buttons, the only other widget to be changed is switches. When GTK first introduced switches, they were a fairly new concept on the desktop. For this reason, they included explicit “ON” and “OFF” labels, in order to communicate how the switches operated. Since then, switch widgets have become ubiquitous, and users have become familiar with switches that don’t contain labels.

The latest Adwaita changes bring the theme into line with other platforms and make switches more compact and modern in appearance, by removing the labels and introducing a more rounded shape.

Elsewhere, no change

Aside from the changes described above, very little has changed in Adwaita. The vast majority of widgets remain the same, albeit with very slightly altered colours. Generally, UI layouts shouldn’t alter and users should feel comfortable with the changes.

Spot the difference (the old version of Adwaita is on the left and the new version is on the right):

Conclusion

Please try the new theme. We hope you like it!

And we appreciate your feedback—in particular if you are a GTK application developer. You can provide it on irc (in the #gtk+ channel on GimpNet) or via the gtk-devel-list mailing list, or by filing an issue in gitlab.

A report from the Guadec GTK+ BoF

The GTK+ team had a full day planning session during the BoF days at Guadec, and we had a full room, including representatives from several downstreams, not just GNOME.

We had a pretty packed agenda, too.

GTK+ 3

We started out by reviewing the GTK+ 3 plans that we’ve outlined earlier.

In addition to what was mentioned there, we also plan to backport the new event controllers, to make porting to GTK+ 4 easier. We will also add meson build support to help with Windows builds.

The 3.24 releases will effectively be a continuation of the 3.22 branch and should be entirely safe to put out as stable updates in distributions.

We plan to release GTK+ 3.24.0 in time for GNOME 3.30.

GTK+ 4 leftovers

The bulk of the day was taken up by GTK+ 4 discussion. We’ve reviewed the list of leftover tasks on the roadmap:

  • Finish DND: Gestures on the GTK+ level, local shortcuts
  • Introduce GtkToplevel and cleanly support popovers
  • Add transformations
  • Create a shortcuts event controller to replace key bindings
  • Port GtkTextView to render nodes
  • Profile the cairo backend, make sure its performance is on par with GTK+ 3
  • Port various dependent libraries:
    • vte
    • webkit
    • libchamplain
    • gtk-vnc
    • gtk-spice

Most of these tasks have names next to them, but if you want to help with any of these tasks, by all means, contact us!

Noticeably absent from this list are a few things that were on the roadmap before:

  • Constraint-based layout (emeus)
  • Shader compiler and application provided shaders
  • Designer support

All of these can still happen if merge requests appear, but we don’t think that we should block on them. They can be developed externally to GTK+ 4, and become GTK+ 5 material.

GTK+ backends

We spent some time evaluating the state of GDK backends in GTK+ master.

The Windows backend is in OK shape. We have several people who help with maintenance and feature development for it, meson makes building it a lot easier, and we have ci for it.

The Quartz backend is in a much worse state. It has not been kept in buildable shape, nobody is providing fixes or feature development for it, and we don’t have ci. We had a macbook offered that could be used for ci, and it was suggested that we could use travis ci for the OS X.

GTK+ timeline

We spent a long time on this, and did not reach a 100% consensus, but it seems realistic to aim for a GTK+ 4 release in spring of 2019, if we keep making good progress on the outstanding leftovers.

When we release GTK+ 3.96, we will also announce a date for GTK+ 4.0. We hope to be able commit to release before GNOME 3.32, so GNOME application developers can switch their master branches to GTK+ 4 without worrying about whether that will disrupt other development for 3.32.

Application porting

We really want feedback from application ports at this point. But we are in a bit of a difficult position, since we can’t plausibly claim to be done with major API work until the GtkToplevel and shortcuts controller work is done.

Our recommendation to app authors at this point is:

  • If you are a bit adventurous, do a port to 3.94 on a branch. It should be possible to keep it working without too much work during the remainder of GTK+ 4 development.
  • If you are not quite as adventurous, wait until 3.24 is released, use it to prepare your port, and port to GTK+ 3.96.
  • Either way, please make your port available to users for testing, either as a regular release, or as a Flatpak with a bundled GTK+.

GLib diversion

In the afternoon, we spent a while talking about GLib. We went over a laundry list of larger and smaller items. Notable highlights: GProperty may happen for 2.60 and we may be able to use g_autoptr soon.

Other ideas

We discussed a great number of other things that we could and should do.

For example, it was suggested (and generally agreed to) that we should merge gsk into gdk, since it is small and the internals are somewhat intertwined. It was also suggested to create subdirectories in gtk/, for example for the css machinery.

GTK+ 3.94

Today, we released GTK+ 3.94.0. Again, it has been a while since the last release, so it is worth summarizing whats new in this release. There is really too much here to cover it all, so this post will only highlight the most important changes.

This release is another milestone on our way towards GTK+ 4. And while there are still some unfinished things, this release is much closer to we hope to achieve with GTK+ 4.

GSK

The Broadway backend now has a GskRenderer, so the future for Broadway looks much better.

We introduced a new type of render node, GskOffsetNode, which is a simplified GskTransformNode and takes over the job of translating content as we move up and down the render node tree. With this change, we are now able to cache render nodes for widgets over multiple frames, and reposition them if necessary.

We also introduced GskDebugNodes, which take over node names, and let us simplify some of the GTK+ apis for creating render nodes.

When falling back to cairo for rendering, we now use recording surfaces instead of image surfaces, so we can replay the rendering at a different scale.

An important new operation is gsk_render_node_diff to compare two render node trees (see below for more on this).

GDK

Following the general trend of aligning the GDK apis with Wayland instead of X, GdkWindow was renamed to GdkSurface.

The GdkTexture api has been refined, with new GdkMemoryTexture and GdkGLTexture subclasses, and a powerful new abstraction, GdkPaintable, has been introduced.

A GdkPaintable represents an object that can be painted anywhere at any size without requiring any sort of layout. This is inspired by similar concepts elsewhere, such as ClutterContent, HTML/CSS Paint Sources or SVG Paint Servers. To show off the power of this concept, a few new demos have been added in gtk4-demo:

The DND code continues to see major refactorings. It now uses the same content-provider infrastructure that was introduced in 3.93 for clipboard handling, and it has separate objects for the source and target side of a DND operation. More changes will be coming here.

GTK

widgets

GTK+ has gained support for showing videos, with the GtkVideo and GtkMediaControls widgets, and there is also a new GtkPicture widget to split off image viewing from GtkImage (which is really about icons).

GtkFontChooser allows tweaking OpenType features and font variations, and Ctrl-Shift-e for color Emoji input has been replaced with completion that can be enabled with the GtkEntry::enable-emoji-completion property.

Input

The event-specific signals in GtkWidget continue to disappear. At this point only ::event is left, but it will go away too. Instead, we are using event controllers, and several new ones have been added to cover all needed events:

  • GtkEventControllerMotion
  • GtkEventControllerKey
  • GtkGestureStylus

To make this transition easier, it is now possible to create event controllers in ui files.

Wayland has its own platform input method, based on the Wayland text protocol.

Drawing

The ::draw signal has been removed, all widgets have to implement ::snapshot. They can now create their own GtkSnapshot instances for intermediate rendering. Clipping is no longer applied on the GTK+ level – widgets are free to draw outside their allocation, if that is what is required.

Widget invalidation has been changed, it now works by discarding the cached render nodes of invalidated widgets, and recreating the missing parts of the render node tree.

For finding the region that needs to be redrawn, GTK+ diffs the render node trees of the previous and the current frame, and applies some heuristics to keep the number of rectangles from growing too large.

The GTK+ inspector lets you track invalidations, which you can see in action here:

Other changeS

GTK+ no longer supports generic loadable modules. Input methods, print backends and media backends have been converted to GIOModules and extension points.

The platform im modules (i.e. the Windows, Wayland, Broadway im contexts)  are always included and will be enabled by default on their platform.

The Vulkan support in GDK can now use a particular device that is specified by the GDK_VULKAN_DEVICE environment variable. Use GDK_VULKAN_DEVICE=list to see all availble devices.

Try it out

With GTK+ 3.94.0, it should be possible to start porting applications. The documentation has an initial porting guide.

A GTK+ 3 update

Plans

When we started development towards GTK+ 4, we laid out a plan that said GTK+ 3.22 would be the final, stable branch of GTK+ 3.  And we’ve stuck to this for a while.

I has served us reasonably well — GTK+ 3 stopped changing in drastic ways, which was well-received, and we are finally seeing applications moving from GTK+ 2.

Reality

But, GTK+ 4 is taking its time to mature (more on that in another post), and some nice new features (such as font variation support, or Emoji completion) languish unused in master. We also get requests for critical APIs from some of the ported applications.

Therefore, we have decided that it is better to change course and allow a limited amount of new features and API in GTK+ 3.x, by doing a GTK+ 3.24 release in September.

There is now a gtk-3-24 branch in git. GTK+ 3.x maintenance has moved to that branch, and we won’t be doing any further 3.22.x releases.

Highlights

The first release off this new branch is GTK+ 3.23.0, which can be found here:

https://download.gnome.org/sources/gtk+/3.23/gtk+-3.23.0.tar.xz

The highlights of this release include new font chooser features,

  • Allow setting OpenType font features
  • Show examples for OpenType font features
  • Allow selecting OpenType font variations
  • Support levels of details for selection

new Emoji features,

  • Support a completion popup for Emoji
  • Drop Ctrl-Shift-e shortcut

gdk_window_move_to_rect as public API,

and the Wayland backend using anonymous shared memory on FreeBSD.

Numerology

A side-effect of doing one more 3.x cycle is that we will have GTK+ 3.24 to be the final GTK+ 3, which is a pleasant parallel to GTK+ 2.24 being the final GTK+ 2.

Input methods in GTK+ 4

GTK’s support for loadable modules dates back to the beginning of time, which is why GTK has a lot of code to deal with GTypeModules and with search paths, etc. Much later on, Alex revisited this topic for GVfs, and came up with the concept of extension points and GIO modules, which implement them.  This is a much nicer framework, and GTK 4 is the perfect opportunity for us to switch to using it.

Changes in GTK+ 4

Therefore, I’ve recently spent some time on the module support in GTK. The major changes here are the following:

  • We no longer support general-purpose loadable modules. One of the few remaining users of this facility is libcanberra, and we will look at implementing ‘event sound’ functionality directly in GTK+ instead of relying on a module for it. If you rely on loading GTK+ modules, please come and talk to us about other ways to achieve what you are doing.
  • Print backends are now defined using an extension point named “gtk-print-backend”, which requires the type GtkPrintBackend.  The existing print backends have been converted to GIO modules implementing this extension point. Since we have never supported out-of-tree print backends, this should not affect anybody else.
  • Input methods are also defined using an extension point, named “gtk-im-module”, which requires the GtkIMContext type.  We have dropped all the non-platform IM modules, and moved the platform IM modules into GTK+ proper, while also implementing the extension point.

Adapting existing input methods

Since we still support out-of-tree IM modules, I want to use the rest of this post to give a quick sketch of how an out-of-tree IM module for GTK+ 4 has to look.

There are a few steps to convert a traditional GTypeModule-based IM module to the new extension point. The example code below is taken from the Broadway input method.

Use G_DEFINE_DYNAMIC_TYPE

We are going to load a type from a module, and G_DEFINE_DYNAMIC_TYPE is the proper way to define such types:

G_DEFINE_DYNAMIC_TYPE (GtkIMContextBroadway,
                       gtk_im_context_broadway,
                       GTK_TYPE_IM_CONTEXT)

Note that this macro defines a gtk_im_context_broadway_register_type() function, which we will use in the next step.

Note that dynamic types are expected to have a class_finalize function in addition to the more common class_init, which can be trivial:

static void
gtk_im_context_broadway_class_finalize
               (GtkIMContextBroadwayClass *class)
{
}

Implement the GIO module API

In order to be usable as a GIOModule, a module must implement three functions: g_io_module_load(), g_io_module_unload() and g_io_module_query() (strictly speaking, the last one is optional, but we’ll implement it here anyway).

void
g_io_module_load (GIOModule *module)
{
  g_type_module_use (G_TYPE_MODULE (module));
  gtk_im_context_broadway_register_type  
                        (G_TYPE_MODULE (module));
  g_io_extension_point_implement
             (GTK_IM_MODULE_EXTENSION_POINT_NAME,
              GTK_TYPE_IM_CONTEXT_BROADWAY,
              "broadway",
              10);
 }
void
g_io_module_unload (GIOModule *module)
{
}
char **
g_io_module_query (void)
{
  char *eps[] = {
    GTK_IM_MODULE_EXTENSION_POINT_NAME,
    NULL
  };
  return g_strdupv (eps);
}

Install your module properly

GTK+ will still look in $LIBDIR/gtk-4.0/immodules/ for input methods to load, but GIO only looks at shared objects whose name starts with “lib”, so make sure you follow that convention.

Debugging

And thats it!

Now GTK+ 4 should load your input method, and if you run a GTK+ 4 application with GTK_DEBUG=modules, you should see your module show up in the debug output.

 

GTK+ 3.92

Yesterday, we released GTK+ 3.92.1, 重庆市. Since it has been a while since the last 3.91 release, here is a brief look at the major changes.

This release is another milestone on our way towards GTK+ 4. And while a lot still needs to be done, this release allows a first glimpse at some of the things we hope to achieve in GTK+ 4.

GSK

Much of the work since the last release has gone into GSK. The Vulkan renderer is now close to complete, as far as avoiding cairo fallbacks goes. The only missing piece are blurred shadows (admittedly, an important piece).

One major step forward since the 3.91.2 release is that we no longer use cairo fallbacks for all text. Instead, text (in labels and entries, sadly not in text views yet) gets translated into text nodes. Each text node contains a PangoGlyphString and a PangoFont. The Vulkan renderer uses a glyph cache to avoid re-rendering the glyphs for each frame.

The internal logic of the Vulkan renderer has been reworked to use textures instead of cairo surfaces for intermediate results and thus avoid more cairo fallbacks.

Other node types that have gained support in the Vulkan renderer include blurs, repeat nodes, blend modes and cross-fades. In some cases, the shaders we use are very naive implementations. Help with improving them would be more than welcome!

As a first example of what we can do with render nodes, we have implemented a blur-under feature for GtkOverlay. This works by capturing the ‘main child’ of the overlay as a render node, and then reusing it several times, with the right clipping, and sometimes with a blur node.

Inspector

To help you explore GSK, the inspector now shows Vulkan information and the recorder shows a lot more information about render nodes.

Input

On the input side, events have gained accessors, and we are no longer accessing their fields directly. This is an intermediate step, cleaning up events is still a work in progress. We have moved the traditional widget signals for events (such as ::key-press-event) to an event controller, and most widgets inside GTK+ have stopped using them altogether.

Build System

We have switched over to using Meson exclusively for GTK+, and the 3.92.1 release is the first one done using Meson’s dist support. To get the release out the door, we also had to port the documentation, the test suite and the installed tests to using Meson.

There are still some rough edges (we don’t get all dependencies 100% right), but overall, Meson worked out well for us.

The rest

Of course, everybody loves Emoji, and the same color Emoji support that has landed in GTK+ 3.22 is also available in this release. Beyond that, font support in CSS has improved a bit with support for the CSS3 font-variant property.

Of course, this relies on fonts that have the corresponding features.

Try it out

With GTK+ 3.92.1, it should be easy to try some of these things out for yourself.

And if you’ve always wanted to get into GTK+ development but never found the right opportunity, now is a great time to get involved!