What is Edje?

Edje is a complex graphical design & layout library.

It doesn’t intend to do containing and regular layout like a widget set, but it is the base for such components. Based on the requirements of Enlightenment 0.17, Edje should serve all the purposes of creating visual elements (borders of windows, buttons, scrollbars, etc.) and allow the designer the ability to animate, layout and control the look and feel of any program using Edje as its basic GUI constructor. This library allows for multiple collections of Layouts in one file, sharing the same image and font database and thus allowing a whole theme to be conveniently packaged into 1 file and shipped around.

Edje separates the layout and behavior logic. Edje files ship with an image and font database, used by all the parts in all the collections to source graphical data. It has a directory of logical part names pointing to the part collection entry ID in the file (thus allowing for multiple logical names to point to the same part collection, allowing for the sharing of data between display elements). Each part collection consists of a list of visual parts, as well as a list of programs. A program is a conditionally run program that if a particular event occurs (a button is pressed, a mouse enters or leaves a part) will trigger an action that may affect other parts. In this way a part collection can be “programmed” via its file as to hilight buttons when the mouse passes over them or show hidden parts when a button is clicked somewhere etc. The actions performed in changing from one state to another are also allowed to transition over a period of time, allowing animation. Programs and animations can be run in “parallel”.

This separation and simplistic event driven style of programming can produce almost any look and feel one could want for basic visual elements. Anything more complex is likely the domain of an application or widget set that may use Edje as a convenient way of being able to configure parts of the display.

So how does this all work?

Edje internally holds a geometry state machine and state graph of what is visible, not, where, at what size, with what colors etc. This is described to Edje from an Edje .edj file containing this information. These files can be produced by using edje_cc to take a text file (a .edc file) and “compile” an output .edj file that contains this information, images and any other data needed.

The application using Edje will then create an object in its Evas canvas and set the bundle file to use, specifying the group name to use. Edje will load such information and create all the required children objects with the specified properties as defined in each part of the given group.

Edje is an important EFL component because it makes easy to split logic and UI, usually used as theme engine but can be much more powerful than just changing some random images or text fonts.

Edje also provides scripting through Embryo and communication can be done using messages and signals.

See also

Before digging into changing or creating your own Edje source (edc) files, read the Edje Data Collection reference .

Signals from the edje object

You can debug signals and messagges by capturing all of them, example:

def sig_dbg(obj, emission, source):
    print(obj, emission, source)

def msg_dbg(obj, msg):
    print(obj, msg)

my_edje.signal_callback_add("*", "*", sig_dbg)

Inheritance diagram

Inheritance diagram of efl.edje