View source for Sugar Architecture Temp

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This page describes the components in which Sugar is divided and gives pointers to the relevant parts of the source code. The intention is to give a starting point to the people that want to start hacking on Sugar.

Sugar is mainly coded in python making extensive use of PyGTK and dbus-python. Other dependencies are pango, cairo, telepathy, matchbox, avahi, gstreamer, rsvg, xapian, hippo-canvas, vte, ... {{pending|TODO: complete this list}}.

== Components ==

In order to understand how these components map to the user-visible elements, familiarity with [[OLPC Human Interface Guidelines]] is required.

=== Shell ===

Code: http://dev.laptop.org/git?p=sugar;a=tree;f=shell

The Sugar Shell is the UI component that provides the following services to the user:

* starting, stopping and joining activities,
* managing devices (network connection, battery, etc),
* managing the clipboard,
* managing groups of buddies.

Basically, all that the user does outside activities is done in the shell.

The shell can be divided in two major components, the Frame and the Home view.

Code: http://dev.laptop.org/git?p=sugar;a=tree;f=shell/view/frame

The frame is implemented as four top level windows that cover the border of the screen when visible. Every side of the frame contains icons organized in trays (gtk.Toolbar). See [[OLPC Human Interface Guidelines/The Laptop Experience/The Frame]].

Code: http://dev.laptop.org/git?p=sugar;a=tree;f=shell/view/home

The home view is a top-level window with the DESKTOP hint. The three zoom levels are implemented as hippo.Canvas embedded in that window. See [[OLPC Human Interface Guidelines/The Laptop Experience/Zoom Metaphor]].

=== Activities ===

What are called applications or programs in other environments, are activities in Sugar, see [[OLPC Human Interface Guidelines/Activities]].

Activity authors need to understand how the activity concept is different from traditional applications and how its software can make better use of the Sugar platform.

Activities can happen in isolation or in collaboration with other users.

What is a correct activity from the implementation point of view:

* a top level X window with some predefined properties, see [[Low-level Activity API#X Properties]],
* behaves properly when running inside [[Rainbow]], see [[Low-level_Activity_API#Security]],
* saves its state to the Datastore when needed, see [[Low-level_Activity_API#Datastore]],
* can resume that state so the user is confronted with the same state as when the activity was closed,
* provides a D-Bus service that the shell can use, see [[Low-level_Activity_API#DBus Methods]],
* can collaborate, that means that its state is shared between several instances running each on an XO, see [[Low-level_Activity_API#Presence]].

Activities can choose between using the low level APIs presented above, or the higher-level [[Sugar_Architecture#Activity_API]] presented below.

=== Shell service ===

Code: http://dev.laptop.org/git?p=sugar;a=tree;f=services/shell

The shell service provides the following subservices to the Shell:

* clipboard: store clippings, this is basically the backend of the clipboard tray in the left frame,
* activity registry: manages a registry of the installed activities,
* object type registry: maintains a mapping of mime type to "umbrella" types, these are high level object types like Image, Audio, Video, etc that are used to give the user an uniform view of objects in the clipboard and in the journal.

These services are offered as D-Bus interfaces.

=== Journal ===

Code: http://dev.laptop.org/git?p=journal-activity;a=tree

The Journal keeps track of what the user has done with the laptop. Every activity should keep records in the journal so the user can see what has been done in the past and probably resume some past activity.

All this data produced by the activities is kept by the Datastore service, and the journal provides to the user different ways of querying and browsing past works.

=== Datastore service ===

Code: http://dev.laptop.org/git?p=projects/datastore;a=tree

Provides activities with a way to store data and metadata and the journal with means for querying, including full text search.

=== Presence service ===

Code: http://dev.laptop.org/git?p=projects/presence-service;a=tree

See [[Presence_Service]].

=== Activity API ===

Code: http://dev.laptop.org/git?p=sugar;a=tree;f=lib

This API aims to make the development of new activities as simple and straightforward as possible.

Currently it is only available to activities implemented in python, but the plan is to gradually rewrite it in C and make available bindings for different languages.

{{pending|TODO: link to the activity API pydocs}}

Contains the following modules:

* activity: contains a base Activity class for activities to subclass, see [[Activity_tutorial]],
* graphics: provides gtk-based widgets that integrate better with Sugar,
* presence: wrapper around the [[Sugar_Architecture#Presence_service]],
* datastore: wrapper around the [[Sugar_Architecture#Datastore]],
* bundle: provides functionality for manipulating [[Bundle]]s,
* clipboard: wrapper around the clipboard service in [[Sugar_Architecture#Shell_service]], instead of accessing the clipboard through this module, activities should make use of the X selection mechanism, see http://en.wikipedia.org/wiki/X_Window_selection. Activities using PyGTK can use [http://www.pygtk.org/pygtk2reference/class-gtkclipboard.html gtk.Clipboard], see also [http://www.pygtk.org/pygtk2tutorial/ch-NewInPyGTK2.2.html#sec-Clipboards Clipboards].

== Specifications ==

* [[OLPC_Human_Interface_Guidelines|Human Interface guidelines]]
* [[Activity Bundles]]
* [[Sugar Icon Format]]
* [[Activity Protocol]]

== [[Sugar Architecture/API | API]] ==
* [[Low-level Activity API]]
* [[Presence Service DBus API]]
* [[HippoCanvas]]: Cairo drawing and UI layout widget

== Third party packages ==
* [http://www.avahi.org/wiki/ProgrammingDocs Avahi] service discovery layer
* [http://cairographics.org/documentation Cairo] 2D graphics library ([http://cairographics.org/pycairo Python interface])
* [http://developer.gnome.org/doc/API/2.0/pango/ Pango] text layout library ([http://www.pygtk.org/docs/pygtk/pango-class-reference.html Python interface])
* [http://www.gtk.org/api/ GTK+] user interface ([http://www.pygtk.org/docs/pygtk/index.html Python interface])
* [http://dbus.freedesktop.org/doc/dbus-tutorial.html D-Bus] interprocess communications system ([http://dbus.freedesktop.org/doc/dbus-python/doc/tutorial.html Python interface])

== Links and references ==
[http://www.python.org/doc/ Python Documentation]