GtkIconTheme API gives access to icons that are shipped with the icon
Icon themes are sets of icons that share a common look and feel; a theme is a mapping between a name and an icon file and size.
For more information on icon themes, you can read the freedesktop.org icon theme specification
Extending the icon theme¶
Some times, applications need icons that are too domain-specific to be included in a generic icon theme.
The standard practice for this is to extend the icon theme by installing the
icons in a directory structure that matches the hicolor icon theme. Typically,
the icons will be located in your application’s datadir, e.g.
For instance, you can install icons from your Meson build file:
# Define PKG_DATADIR as a global symbol pkg_datadir = get_option('prefix') / get_option('datadir') / meson.project_name() add_project_arguments('-DPKG_DATADIR=@0@'.format(datadir), language: 'c') action_icons_dir = pkg_datadir / 'icons/hicolor/16x16/actions' action_icons = [ 'action-name-1.png', 'action-name-2.png', ] install_data(action_icons, install_dir: action_icons_dir)
You will also need to tell
GtkIconTheme to look in that directory:
GtkIconTheme *theme = gtk_icon_theme_get_for_display (gdk_display_get_default ()); gtk_icon_theme_append_search_path (theme, PKG_DATADIR "/icons");
It is recommended to follow the principles of the icon naming specification even for these private icons.
This approach to icon theme extension has some advantages over others:
the application-specific icons don’t pollute the shared namespace for themed icons, and other applications won’t unintentionally pick up an icon that was only meant for your application
since the icons are installed into a directory below ‘hicolor’, the theme can override the icons to make your application fit in with the rest of the system
It is possible to include application-specific icons directly in the application binary as resources, instead of installing them in the file system. By using resources you reduce the performance penalty of seeking files on the file system, and you improve the portability and reliability of your application. The downsides are that changing icons requires rebuilding your application, and that the size of the binary grows.
To use resources, place your icons in a directory structure that matches the hicolor icon theme:
<gresources> <gresource prefix="/my/resources/icons/16x16/actions"> <file>icon1.png</file> <file>icon2.png</file> ... </gresource> </gresources>
When using resources, we don’t include ‘hicolor’ in the path.
GtkIconTheme about the resource path where your icons are located:
GtkIconTheme *theme = gtk_icon_theme_get_for_display (gdk_display_get_default ()); gtk_icon_theme_add_resource_path (theme, "/my/resources/icons");
GtkApplication automatically sets up a resource path based on the
application id of your application. If your applications id is ‘org.my.App’,
then icons will be looked for under “/org/my/App/icons”.
Some icons benefit from being ‘flipped’ in right-to-left (RTL) locales. GTK does
this automatically, by passing a
GTK_ICON_LOOKUP_DIR_LTR flag to
GtkIconTheme when loading icons.
If you are loading icons manually using the
GtkIconTheme API, you may want to do
the same for icons where flipping is relevant.
Of course, RTL variants must be present in the icon theme for this to make any
difference. If you have an icon with an RTL variant, you should append the
-rtl suffix to the icon’s file base name.
Symbolic icons have a simple form, and can be used much like text. The will be
recolored according to the context in which they are used. By convention,
symbolic icons are named with a
Passing an icon name like “pan-start-symbolic” to GTK functions like
gtk_image_set_from_icon_name() will automatically do the right thing. When
you are manually loading a symbolic icon using the
GtkIconTheme APIs, make sure
to use the ‘symbolic’ variants, such as
gtk_icon_info_load_symbolic() to ensure
that the icon is properly colored.
When installing your own symbolic icons, you can either install an svg (the
traditional form in which symbolic icons are created) or use the
gtk-encode-symbolic-svg utility to convert the icon into specially crafted
.symbolic.png files, which can be installed into the fixed-size subdirectories
of the icon theme:
gtk-encode-symbolic-svg -o /usr/share/icons/hicolor/48x48/apps my-app-symbolic.svg 48x48
The icon theme specification defines a universal fallback theme, called hicolor, in which applications can install icons that need to be known by the rest of the system.
The main example for this is the application icon that is used in the
applications desktop file. This icon should be named to match the application
name, and be installed in
/usr/share/icons/hicolor/48x48/apps/. Other sizes are
optional, but a 256×256 icon is the default size used by GNOME in its
application grid, so you’re strongly encouraged to provide one.
Applications are also encouraged to install a symbolic version of the
application icon into the hicolor theme, with the same name and a
suffix. The symbolic icon will be used in the HighContrast theme. Symbolic icons
can be installed as SVG, in the
(which was added to hicolor in 0.15), or as
.symbolic.png files in
/usr/share/icons/hicolor/48x48/apps/. Other sizes are optional.
Unlike other icons, application icons cannot be added to a GResource, as they are referenced by the desktop file and loaded by the desktop.