99 lines
3.8 KiB
ReStructuredText
99 lines
3.8 KiB
ReStructuredText
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.. _edje_main_intro:
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What is Edje?
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=============
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Edje is a complex graphical design & layout library.
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It doesn't intend to do containing and regular layout like a widget
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set, but it is the base for such components. Based on the requirements
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of Enlightenment 0.17, Edje should serve all the purposes of creating
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visual elements (borders of windows, buttons, scrollbars, etc.) and
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allow the designer the ability to animate, layout and control the look
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and feel of any program using Edje as its basic GUI constructor. This
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library allows for multiple collections of Layouts in one file,
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sharing the same image and font database and thus allowing a whole
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theme to be conveniently packaged into 1 file and shipped around.
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Edje separates the layout and behavior logic. Edje files ship with an
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image and font database, used by all the parts in all the collections
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to source graphical data. It has a directory of logical part names
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pointing to the part collection entry ID in the file (thus allowing
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for multiple logical names to point to the same part collection,
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allowing for the sharing of data between display elements). Each part
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collection consists of a list of visual parts, as well as a list of
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programs. A program is a conditionally run program that if a
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particular event occurs (a button is pressed, a mouse enters or leaves
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a part) will trigger an action that may affect other parts. In this
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way a part collection can be "programmed" via its file as to hilight
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buttons when the mouse passes over them or show hidden parts when a
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button is clicked somewhere etc. The actions performed in changing
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from one state to another are also allowed to transition over a period
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of time, allowing animation. Programs and animations can be run in
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"parallel".
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This separation and simplistic event driven style of programming can produce
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almost any look and feel one could want for basic visual elements. Anything
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more complex is likely the domain of an application or widget set that may
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use Edje as a convenient way of being able to configure parts of the display.
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So how does this all work?
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==========================
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Edje internally holds a geometry state machine and state graph of what is
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visible, not, where, at what size, with what colors etc. This is described
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to Edje from an Edje .edj file containing this information. These files can
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be produced by using edje_cc to take a text file (a .edc file) and "compile"
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an output .edj file that contains this information, images and any other
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data needed.
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The application using Edje will then create an object in its Evas
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canvas and set the bundle file to use, specifying the **group** name to
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use. Edje will load such information and create all the required
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children objects with the specified properties as defined in each
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**part** of the given **group**.
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Edje is an important EFL component because it makes easy to split logic and
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UI, usually used as theme engine but can be much more powerful than just
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changing some random images or text fonts.
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Edje also provides scripting through Embryo and communication can be
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done using messages and signals.
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.. seealso::
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Before digging into changing or creating your own Edje source (edc)
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files, read the `Edje Data Collection reference
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<https://build.enlightenment.org/job/nightly_efl_gcc_x86_64/lastSuccessful
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Buil d/artifact/doc/html/edcref.html>`_ .
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Signals from the edje object
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============================
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You can debug signals and messagges by capturing all of them, example::
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def sig_dbg(obj, emission, source):
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print(obj, emission, source)
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def msg_dbg(obj, msg):
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print(obj, msg)
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my_edje.signal_callback_add("*", "*", sig_dbg)
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my_edje.message_handler_set(msg_dbg)
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API Reference
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=============
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.. toctree::
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:titlesonly:
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module-edje.rst
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Inheritance diagram
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===================
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.. inheritance-diagram:: efl.edje
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:parts: 2
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