Graphical Editing Framework: Difference between revisions

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{{More citations needed|date=January 2024}}

''Just a quick writeup, please review''

The '''Graphical Editing Framework''' '''(GEF)''' is an [[Eclipse (software)|Eclipse]] project that provides framework and end-user components related to graphical applications.<ref>{{Cite web |last=Web |first=Eclipse |date=2013-01-31 |title=Eclipse Graphical Editing Framework (GEF) |url=https://projects.eclipse.org/projects/tools.gef |access-date=2024-01-12 |website=projects.eclipse.org |language=en}}</ref>

== LinksHistory ==

Graphical Editing Framework is a framework that was developed for the [[eclipse]] platform. It is known as a framework with a very steep learning curve, but it offers some benefits.

GEF was initially developed as part of IBM's etools (<code>com.ibm.etools.gef</code>) and was contributed to [[Eclipse (software)|Eclipse]] in 2002 in version 2.0.0, consisting then of two components: Draw2d, a 2D visualization component based on the [[Standard Widget Toolkit|Standard Widget Toolkit (SWT)]] and GEF (MVC), a related model-view-controller framework that can be used to realize graphical editors as part of Eclipse Rich Client Platform (RCP) applications. The first release at Eclipse was GEF 2.1.0 in March 2003. The next major version, GEF 3.0.0, was released in June 2004, providing many new features like support for rules and guides. Zest was added as a third project component in 2007 in version 1.0.0 as part of the GEF 3.4.0 release. Since 2004, when GEF 3.0.0 was released, only compatible changes have been applied to the framework's [[API|application programming interface]] (API).

A new major revision of the framework has been developed in parallel to the maintenance of the GEF 3.x components by the project team since 2010. It is a complete redesign that is much more modular, uses JavaFX instead of SWT as underlying rendering framework, and can be used also independently of Eclipse RCP applications. Commonly referred to as GEF4, its components were initially released in version 0.1.0 (with still provisional API) in June 2015 as part of the GEF 3.10.0 (Mars) release. The GEF4 components are to be published in version 1.0.0 as part of the GEF 4.0.0 (Neon) release in June 2016.

GEF consists of the following components

*[[draw2d]] has to be used for the View components

* Requests/Commands have to be used to edit the model

* ''Palette'' of Tools that are offered to the user

== BenefitsGEF 3.x ==

GEF 3.x provides framework technology to realize graphical editors and views as part of [[Eclipse (software)#Rich Client Platform|Eclipse Rich Client Platform (RCP)]] applications. It is internally decomposed into three components:

* Draw2d – A 2D visualization component based on the [[Standard Widget Toolkit|Standard Widget Toolkit (SWT)]]

* GEF (MVC) - A model-view-controller component that can be used to realize graphical editors as part of Eclipse Rich Client Product (RCP) applications

* Zest - A graph-based visualization toolkit that can be used to realize views for visualization of graph-like data structures as part of Eclipse RCP applications

While graphical applications can be built on top of the GEF 3.x components directly, Draw2d and GEF (MVC) are also used by the [[Graphical Modeling Framework|Graphical Modeling Framework (GMF)]], which combines them with the [[Eclipse Modeling Framework|Eclipse Modeling Framework (EMF)]] to create the code for both the data model and the graphical editor.

== Benefits ==

* Having a Graphical Representation and being able to edit it

* Predefined Tools for Selection, Connection Creation and others.

* [[MVC]] (Model View Controller) Concept

=== MVC ConceptArchitecture ===

Editors created with GEF consists(MVC) consist of the following components:

Model: The model has to be implemented by the user or it exists already in case of a legacy software.

* The diagram editor including tool palette

* Figures which graphically represent the underlying data model elements

* EditParts which match figures and their respective model elements

* Request objects for user input

* EditPolicy objects which evaluate the requests and create appropriate command objects

* Command objects that edit the model and provide [[undo]]-redo

==== Design pattern usage ====

Controller: The EditPart acts as a controller. Usually a GraphicalEditPart is chosen. For each model element, including connections, a specific EditPart has to be implemented. Listeners for the model have to be registered in the function EditPart.activate() and have to be unregistered within EditPart.deactivate(). If a model change is detected the view has to be updated accordingly. The EditPart knows both the model and the view. The view has to be created within .createFigure().

GEF makes heavy use of [[design pattern]]s. These patterns are often mandatory under GEF and developers are required to understand them.

* [[Model-View-Controller]] is an architectural design pattern which divides an application into separate parts which communicate with each other in a specific way. The goal is to separate data model (model), [[graphical user interface]] (view) and [[business logic]] (controller). GEF uses the MVC pattern extensively.

** Model: The data model hascan toeither be generated using EMF, self-implemented by the user or it existsmay already exist in case of a legacy software.

** Controller: The EditParts act as controllers. Typically, each model element has its matching EditPart. EditParts may contain other EditParts thereby matching model elements containing other model elements. EditParts also have a reference to the figure which graphically represents the model element. Finally, EditParts evaluate requests and create the appropriate command to edit the underlying model.

** View: For each element within the model, including connections, a Viewfigure has to be implemented, using [[draw2d]]. In order to implement the view,Draw2d anframework. implementation of IFigure ofOftentimes the [[draw2d]]figure libraryis hassome to begeometrical useddrawing.

* [[Factory pattern|Factory]]: Creating models from palette, creating EditParts and creating Figures

* [[Observer pattern|Observer]]: Typically a controller (EditPart) listening on Model and View

* [[Command pattern|Command]]: To implement Undo and Redo functions

* [[Strategy pattern|Strategy]]: EditParts can install and remove EditPolicies dynamically

* [[Chain-of-responsibility pattern|Chain of responsibility]]: To decide which EditPolicy should handle a Request

==== Request and response mechanism ====

View: For each element within the model, including connections, a View has to be implemented, using [[draw2d]]. In order to implement the view, an implementation of IFigure of the [[draw2d]] library has to be used.

Any user action with the editor can generate a request. The nature of the request is understood by the context of invocation. The context is determined by the EditPart the user interacts with and the active tool. The tool can be any selected entry in a tool palette. The request is handed over to the selected EditPart, which in turn returns a Command.

This is achieved using the [[Chain-of-responsibility pattern|chain of responsibility]] mechanism over Editpolicies. The editpolicies determine if they can handle the request, otherwise they pass on to the next editpolicy. The order of declaration of editpolicies determine the order in which the request is passed around. The capable editpolicy creates a command. This command is handed back to the tool which initiated the "Request". Execution of the command causes the model to be modified (Response).

== Links ==

[http://www-128.ibm.com/developerworks/opensource/library/os-gef/ Create an eclipse-based application using the Graphical Editing Framework]

==References==

{{Reflist}}

==External links==

* [https://github.com/eclipse/gef-classic GEF Source Repository]

{{Eclipse Foundation}}

[[Category:Graphics software]]

[[Category:Eclipse (software)]]