Applications and libraries often contain binary or textual data that is
really part of the application, rather than user data. For instance
#GtkBuilder .ui files, splashscreen images, GMenu markup XML, CSS files,
icons, etc. These are often shipped as files in
manually included as literal strings in the code.
The #GResource API and the [glib-compile-resources][glib-compile-resources] program provide a convenient and efficient alternative to this which has some nice properties. You maintain the files as normal files, so its easy to edit them, but during the build the files are combined into a binary bundle that is linked into the executable. This means that loading the resource files are efficient (as they are already in memory, shared with other instances) and simple (no need to check for things like I/O errors or locate the files in the filesystem). It also makes it easier to create relocatable applications.
Resource files can also be marked as compressed. Such files will be included in the resource bundle in a compressed form, but will be automatically uncompressed when the resource is used. This is very useful e.g. for larger text files that are parsed once (or rarely) and then thrown away.
Resource files can also be marked to be preprocessed, by setting the value of the
preprocess attribute to a comma-separated list of preprocessing options.
The only options currently supported are:
xml-stripblanks which will use the xmllint command
to strip ignorable whitespace from the XML file. For this to work,
XMLLINT environment variable must be set to the full path to
the xmllint executable, or xmllint must be in the
the preprocessing step is skipped.
to-pixdata (deprecated since gdk-pixbuf 2.32) which will use the
gdk-pixbuf-pixdata command to convert images to the #GdkPixdata format,
which allows you to create pixbufs directly using the data inside the
resource file, rather than an (uncompressed) copy of it. For this, the
gdk-pixbuf-pixdata program must be in the
PATH, or the
GDK_PIXBUF_PIXDATA environment variable must be set to the full path to the
gdk-pixbuf-pixdata executable; otherwise the resource compiler will abort.
to-pixdata has been deprecated since gdk-pixbuf 2.32, as #GResource
supports embedding modern image formats just as well. Instead of using it,
embed a PNG or SVG file in your #GResource.
json-stripblanks which will use the
json-glib-format command to strip
ignorable whitespace from the JSON file. For this to work, the
JSON_GLIB_FORMAT environment variable must be set to the full path to the
json-glib-format executable, or it must be in the
otherwise the preprocessing step is skipped. In addition, at least version
json-glib-format is required.
Resource files will be exported in the GResource namespace using the
combination of the given
prefix and the filename from the
alias attribute can be used to alter the filename to expose them at a
different location in the resource namespace. Typically, this is used to
include files from a different source directory without exposing the source
directory in the resource namespace, as in the example below.
Resource bundles are created by the [glib-compile-resources][glib-compile-resources] program which takes an XML file that describes the bundle, and a set of files that the XML references. These are combined into a binary resource bundle.
An example resource description: |[
This will create a resource bundle with the following files: |[ /org/gtk/Example/data/splashscreen.png /org/gtk/Example/dialog.ui /org/gtk/Example/menumarkup.xml /org/gtk/Example/example.css ]|
Note that all resources in the process share the same namespace, so use Java-style path prefixes (like in the above example) to avoid conflicts.
You can then use [glib-compile-resources][glib-compile-resources] to compile the XML to a
binary bundle that you can load with g_resource_load(). However, its more common to use the --generate-source and
--generate-header arguments to create a source file and header to link directly into your application.
This will generate
unregister_resource() functions, prefixed by the
--c-name argument passed
the generated #GResource object. The register and unregister functions
register the resource so its files can be accessed using
Once a #GResource has been created and registered all the data in it can be accessed globally in the process by using API calls like g_resources_open_stream() to stream the data or g_resources_lookup_data() to get a direct pointer to the data. You can also use URIs like "resource:///org/gtk/Example/data/splashscreen.png" with #GFile to access the resource data.
Some higher-level APIs, such as #GtkApplication, will automatically load resources from certain well-known paths in the resource namespace as a convenience. See the documentation for those APIs for details.
There are two forms of the generated source, the default version uses the compiler support for constructor
and destructor functions (where available) to automatically create and register the #GResource on startup
or library load time. If you pass
--manual-register, two functions to register/unregister the resource are created
instead. This requires an explicit initialization call in your application/library, but it works on all platforms,
even on the minor ones where constructors are not supported. (Constructor support is available for at least Win32, Mac OS and Linux.)
Note that resource data can point directly into the data segment of e.g. a library, so if you are unloading libraries during runtime you need to be very careful with keeping around pointers to data from a resource, as this goes away when the library is unloaded. However, in practice this is not generally a problem, since most resource accesses are for your own resources, and resource data is often used once, during parsing, and then released.
When debugging a program or testing a change to an installed version, it is often useful to be able to
replace resources in the program or library, without recompiling, for debugging or quick hacking and testing
purposes. Since GLib 2.50, it is possible to use the
G_RESOURCE_OVERLAYS environment variable to selectively overlay
resources with replacements from the filesystem. It is a %G_SEARCHPATH_SEPARATOR-separated list of substitutions to perform
during resource lookups. It is ignored when running in a setuid process.
A substitution has the form
|[ /org/gtk/libgtk=/home/desrt/gtk-overlay ]|
The part before the
= is the resource subpath for which the overlay applies. The part after is a
filesystem path which contains files and subdirectories as you would like to be loaded as resources with the
In the example above, if an application tried to load a resource with the resource path
/org/gtk/libgtk/ui/gtkdialog.ui then GResource would check the filesystem path
/home/desrt/gtk-overlay/ui/gtkdialog.ui. If a file was found there, it would be used instead. This is an
overlay, not an outright replacement, which means that if a file is not found at that path, the built-in
version will be used instead. Whiteouts are not currently supported.
Substitutions must start with a slash, and must not contain a trailing slash before the '='. The path after the slash should ideally be absolute, but this is not strictly required. It is possible to overlay the location of a single resource with an individual file.
- .new(pointer : Pointer(Void), transfer : GICrystal::Transfer)
- .new_from_data(data : GLib::Bytes) : self
.g_type : UInt64
Returns the type id (GType) registered in GLib type system.
#==(other : self) : Bool
trueif this reference is the same as other.
- #_register : Nil
- #_unregister : Nil
- #enumerate_children(path : String, lookup_flags : Gio::ResourceLookupFlags) : Enumerable(String)
- #info(path : String, lookup_flags : Gio::ResourceLookupFlags) : Bool
- #load(filename : String) : Gio::Resource
- #lookup_data(path : String, lookup_flags : Gio::ResourceLookupFlags) : GLib::Bytes
- #open_stream(path : String, lookup_flags : Gio::ResourceLookupFlags) : Gio::InputStream
- #ref : Gio::Resource
- #to_unsafe : Pointer(Void)
- #unref : Nil
true if this reference is the same as other. Invokes