Introduction

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 highlight 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.

For details of Edje's history, see the Edje History section.

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. See the example at Introductory Example.

Although simple, this example illustrates that animations and state changes can be done from the Edje file itself without any requirement in the C application.

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

Edje History

It's a sequel to "Ebits" which has serviced the needs of Enlightenment development for early version 0.17. The original design parameters under which Ebits came about were a lot more restricted than the resulting use of them, thus Edje was born.

Edje is a more complex layout engine compared to Ebits. It doesn't pretend to do containing and regular layout like a widget set. It still inherits the more simplistic layout ideas behind Ebits, but it now does them a lot more cleanly, allowing for easy expansion, and the ability to cover much more ground than Ebits ever could. For the purposes of Enlightenment 0.17, Edje was conceived to 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.

Unlike Ebits, Edje separates the layout and behavior logic.

How to compile

Edje is a library your application links to. The procedure for this is very simple. You simply have to compile your application with the appropriate compiler flags that the pkg-config script outputs. For example:

Compiling C or C++ files into object files:

gcc -c -o main.o main.c `pkg-config --cflags edje`

Linking object files into a binary executable:

gcc -o my_application main.o `pkg-config --libs edje`

See pkgconfig

Next Steps

After you understood what Edje is and installed it in your system you should proceed understanding the programming interface for all objects, then see the specific for the most used elements. We'd recommend you to take a while to learn Ecore, Evas, Eo and Eina as they are the building blocks for Edje. There is a widget set built on top of Edje providing high level elements such as buttons, lists and selectors called Elementary (http://docs.enlightenment.org/auto/elementary/) as they will likely save you tons of work compared to using just Evas directly.

Introductory Example

What follows is a list with various commented examples, covering a great part of Edje's API:

//Compile with:
// edje_cc edje_example.edc && gcc -o edje_example edje_example.c `pkg-config --libs --cflags eina ecore evas ecore-evas edje`
 
#include <Eina.h>
#include <Evas.h>
#include <Ecore.h>
#include <Ecore_Evas.h>
#include <Edje.h>
 
#ifndef PACKAGE_DATA_DIR
#define PACKAGE_DATA_DIR "."
#endif
 
#define WIDTH 320
#define HEIGHT 240
 
static Evas_Object *create_my_group(Evas *canvas, const char *text)
{
   Evas_Object *edje;
 
   edje = edje_object_add(canvas);
   if (!edje)
     {
        EINA_LOG_CRIT("could not create edje object!");
        return NULL;
     }
 
   if (!edje_object_file_set(edje, PACKAGE_DATA_DIR"/edje_example.edj",
                             "my_group"))
     {
        int err = edje_object_load_error_get(edje);
        const char *errmsg = edje_load_error_str(err);
        EINA_LOG_ERR("could not load 'my_group' from edje_example.edj: %s",
                     errmsg);
 
        evas_object_del(edje);
        return NULL;
     }
 
   if (text)
     {
        if (!edje_object_part_text_set(edje, "text", text))
          {
             EINA_LOG_WARN("could not set the text. "
                           "Maybe part 'text' does not exist?");
          }
     }
 
   evas_object_move(edje, 0, 0);
   evas_object_resize(edje, WIDTH, HEIGHT);
   evas_object_show(edje);
   return edje;
}
 
int main(int argc, char *argv[])
{
   Ecore_Evas *window;
   Evas *canvas;
   Evas_Object *edje;
   const char *text;
 
   ecore_evas_init();
   edje_init();
 
   window = ecore_evas_new(NULL, 0, 0, WIDTH, HEIGHT, NULL);
   if (!window)
     {
        EINA_LOG_CRIT("could not create window.");
        return -1;
     }
   canvas = ecore_evas_get(window);
 
   text = (argc > 1) ? argv[1] : NULL;
 
   edje = create_my_group(canvas, text);
   if (!edje)
     return -2;
 
   ecore_evas_show(window);
   ecore_main_loop_begin();
 
   evas_object_del(edje);
   ecore_evas_free(window);
 
   edje_shutdown();
   ecore_evas_shutdown();
 
   return 0;
}

The above example requires the following annotated source Edje file:

// compile: edje_cc edje_example.edc
collections {
   group {
      name: "my_group"; // must be the same as in edje_example.c
 
      parts {
         part {
            name: "background";
            type: RECT; // plain boring rectangle
            mouse_events: 0; // we don't need any mouse event on the background
 
            // just one state "default"
            description {
               state: "default" 0.0; // must always exist
               color: 255 255 255 255; // white
 
               // define part coordinates:
 
               rel1 { // top-left point at (0, 0) [WIDTH * 0 + 0, HEIGHT * 0 + 0]
                  relative: 0.0 0.0;
                  offset: 0 0;
               }
               rel2 { // bottom-right point at (WIDTH * 1.0 - 1, HEIGHT * 1.0 - 1)
                  relative: 1.0 1.0;
                  offset: -1 -1;
               }
            }
         }
 
         part {
            name: "text";
            type: TEXT;
            mouse_events: 1; // we want to change the color on mouse-over
 
            // 2 states, one "default" and another "over" to be used
            // on mouse over effect
 
            description {
               state: "default" 0.0;
               color: 255 0 0 255; // red
 
               // define part coordinates:
 
               rel1 { // top-left at (WIDTH * 0.1 + 5, HEIGHT * 0.2 + 10)
                  relative: 0.1 0.2;
                  offset: 5 10;
               }
               rel2 { // bottom-right at (WIDTH * 0.9 - 6, HEIGHT * 0.8 - 11)
                  relative: 0.9 0.8;
                  offset: -6 -11;
               }
 
               // define text specific state details
               text {
                  font: "Sans"; // using fontconfig name!
                  size: 10;
                  text: "hello world";
               }
            }
 
            description {
               state: "over" 0.0;
               inherit: "default" 0.0; // copy everything from "default" at this point
 
               color: 0 255 0 255; // override color, now it is green
            }
         }
 
         // do programs to change color on text mouse in/out (over)
         programs {
            program {
               // what triggers this program:
               signal: "mouse,in";
               source: "text";
 
               // what this program does:
               action: STATE_SET "over" 0.0;
               target: "text";
 
               // do the state-set in a nice interpolation animation
               // using linear time in 0.1 second
               transition: LINEAR 0.1;
            }
 
            program {
               // what triggers this program:
               signal: "mouse,out";
               source: "text";
 
               // what this program does:
               action: STATE_SET "default" 0.0;
               target: "text";
 
               // do the state-set in a nice interpolation animation
               // using linear time in 0.1 second
               transition: LINEAR 0.1;
            }
         }
      }
   }
}