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Existe una serie de enfoques (stack de software) al desarrollar software para lel ambiente OLPC. El stack que escoja sera fuertemente influenciado en el tipo de configuracion que se necesite y que el desarrollo principal mostrara.

Plataforma base

Ver tambien componentes de software para una discusión sobre el software instalado en la OLPC.

El stack operativo de la OLPC se ve como esto:

• Hardware -- Normalmente una OLPC-XO, pero puede ser otra maquina con Sugar instalada o compilada de forma cruzada.
  • Ver confiuración para las opciones sobre ejecutar Sugar en maquinas diferentes a la XO.
  • Firmware -- la XO usa Open Firmware
• Sistema operativo basado en Fedora Core 7 modificado fuertemente
  • Linux Kernel (2.6.22 con algunos parches 2007-12-15)
• Sistema X Window - tecnología estándar de video X11
• Matchbox - un gestor de ventanas minimalista
• Bitfrost -- Sistema de seguridad
• Servicios D-BUS -- varios servicios específicos a la plataforma (muchas de las operaciones en hardware son expuestas via D-BUS en la XO)
  • Presence Service which uses Telepathy -- RPC entre-maquina para motor de presencia y presencia
• Sugar -- GUI de Shell (escritorio)

Stack del desarrollo de la actividad

esta sección intenta describir a grandes rasgos el stack disponible para el desarrollo de actividades en el ambiente Sugar.

Smalltalk/Etoys

Etoys es una aplicación escrita en Squeak, un ambiente de desarrollo libre hecho en Smalltalk. Smalltalk es uno de los primeros lenguajes orientados a objetos, esto quiere decir, que se ha usado por decadas, y es el resultado de una gran cantidad de componentes y contenido pre-instalado y con recursos que pueden ser usados para crear nuevas actividades.

El ambiente de Etoys es realmente fácil de programar vía una interfaz gráfica de interacciones, y componentes con acceso a funcionalidades especificas del hardware en la laptop. Puedes crear proyectos fascinantes y utiles demostraciones con solo unos clics del puntero y con un poco de lógica.

Ver: Desarrollo de Smalltalk en la XO para comenzar a usar Squeak para desarrollo de la OLPC.

Navegador

Sugar incluye una actividad de Navegador Web basada en Gecko de Mozilla. este navegador incluye HTML, XHTML, Javascript y soporte de SVG. Puedes configurar un simple servidor web en una laptop usando Python, o los niños pueden accesar a las aplicaciones hosteadas en un servidor web público (pero ten en mente que los niños tendrán muy poca conectividad).

Puede desarrollar con esta plataforma sin un hardware en particular o configuración especial, puedes probar usando el Firefox regular durante las etapas iniciales. Es muy fácil portar tu trabajo de donde sea a este stack, y es fácil exportar tu trabajo fuera del proyecto OLPC. El ambiente es, sin embargo, limitado, sin acceso a mucho del hardware o software especial que contiene la laptop.

Componentes de navegador

The built-in Browser is actually just a thin wrapper around the Gecko control. You can use the Gecko control yourself and create web-browser derived activities, either using XUL or Python/PyGTK to instantiate the browser. This gives your Activity access to system services and hardware, at the cost of considerably more complexity.

Ver: ??? para empezar a usar XULRunner/controles web y desarrollar para el OLPC.

Python/PyGTK

Python and GTK based activities are the "standard" way to write software for the OLPC. Using Python and PyGTK is strongly encouraged so that the "View Source" button will normally show the same language wherever the user invokes it. The use of the same language throughout also means that code can often be factored out of one project to be shared with another.

The support for writing activities provided by the core Sugar system (which is itself largely written in Python) is almost always exposed first through Python libraries. On the Sugar platform, PyGTK has access to the following major libraries:

• Cairo -- high performance postscript-like library for drawing vector graphics, with the RSVG SVG-rendering library
• Pango -- flexible text layout system capable of dealing with complex internationalization issues
• D-BUS -- inter-process communications
• Telepathy -- inter-machine RPC and presence management with network traversal and discovery logic (activities are encouraged to use Telepathy's Tubes where practical)
• NumPy -- standard high performance numeric analysis and array-handling module
• CSound -- acoustically modelled sound-synthesis engine (seen in the TamTam activity)
• GStreamer -- general purpose media streaming platform, used for accessing the video camera and playing media
• IPython -- enhanced interactive Python interpreter with syntax highlighting, command-completion and the like

GTK Controls:

• Web Browser Control (HulaHop) -- Gecko 1.9 web browser as a simple embeddable control with Python DOM access
• AbiWord/AbiCollab Control -- AbiWord word processor as an embeddable control with the ability to collaboratively edit with another user
  • This version of AbiWord also includes support for syntax-colouring and collaborative source-code editing
• Evince Control -- PDF and EBook-reading control
• Pygame -- game development engine based on SDL (see OLPCGames), not exactly a control, but close...

in addition to the Python standard library, which includes rather a lot of built-in functionality. One key standard library module is the SQLite database engine, which provides a basic single-user SQL database which can be used by activities for storage.

See: API Reference for a more exhaustive set of pointers to libraries available with links to their documentation

See: Activity tutorial to develop in Python (with PyGTK) for the OLPC.

Activities can use common Python extensions which are installed into their Activity directory. You may also consider rewriting areas that profiling say are problems in your activity as C extensions. This can save both processor load and memory depending on the nature of the extension. Keep in mind, though, that premature optimization is generally not a good idea; code first, optimize later. You can also use extensions to wrap already-existing activities (those not normally Sugar or Python based) by creating a GTK control wrapping your activity's core.

See: #Low Level for a discussion of extensions lower-level programming-language issues

OLPCGames (juegos)

Pygame is a high-level wrapper around the C SDL library, which provides low-level support for developing games. Pygame allows you to easily create raster (pixel-based) graphics for games with reasonable performance thanks to SDL.

OLPCGames is a Python package which allows you to create Sugar Activities using Pygame with access to the special features of the laptop. This includes the Telepathy presence and communications infrastructure and the Pango/Cairo graphics capabilities.

See: Game development HOWTO to start using Python, Pygame and OLPCGames to develop for the OLPC.

See: Game templates for a set of simple templates intended to allow students to create "genres" of games easily

See also Sugargame, a different implementation.

Flash

Sugar inlcuye un motor llamado Gnash de forma predeterminada, y el motor reproductor Adobe Flash puede ser instalado. En este momento no tenemos una herramienta editora de archivos Flash que pueda ser distribuida en las laptops. Sin embargo, si tienes contenido basado en flash, puede ser posible mostrar simplemente ejecutando Gnash en Sugar.

Bajo nivel

Being a regular Fedora 7 Linux machine, the OLPC-XO can run regular Linux i386 executables. However, integration with the Sugar shell is currently a non-trivial exercise. It is often easier to wrap your C/C++/Assembly/Whatever activity in a (normally Python) wrapper than to attempt to implement the entire Low-level Activity API yourself.

See: Low-level Activity API for the most extensive and up-to-date available discussion of how to integrate a low-level activity manually

See: Sugarizing for a (somewhat fragmentary) discussion of how to wrap an existing native-code executable/library with a Python wrapper.

See: Sugarize Demo for a shared library loader hack that provides much of the X11-level functionality for general X11 activities, allowing them to be run largely unchanged on the XO. Most of the special features of the laptop will not be available, but this approach allows for quick porting/testing of activities.

When coding in Python, you will occasionally want access to a C or C++ extension, either one already written, or one written to optimize some part of your activity. You can build these extensions for use under Sugar by using the normal Python distutils with GCC tool chain.

Make sure that you are aware (and respect) the Geode instruction set. It is about the same as the original Athlon instruction set. See the Geode data book linked in the Geode instruction set page.

The best (most reliable and compatible) approach is generally to compile on an official image, using Yum to install the tools required. Doing this on an actual XO, however, is probably not a good idea, as compilation will tend to cause lots of writes to the disk and reduce the longevity of your flash storage chip.

See: Emulation for Compilation for a tip on how to compile using emulation

librerias comunes no disponibles

Mientras que el ambiente de Sugar es rico, no puede incluir todas las posibles librerias o extensiones que aun puedan caber en 200MB. La siguiente lista muestra librerias comunes que no estan disponibles en la XO:

• OpenGL/MESA
• bases de datos relacionales con servidor (MySQL, PostgreSQL)
• Qt/KDE
• Gnome
• Many Kernel-level Linux Drivers (you can build missing drivers yourself, preferably in a throw-away emulator overlay)

Ver tambien

• La pagina de Java incluye una discusión por que java no esta disponible y el prospecto de incluirlo (resumen: la versión libre de Java no estaba disponible hasta hace poco, y ahora que esta, aun falta mucho trabajo para eliminar lo inflado y hacer la experiencia del usuario para que encaje en el paradigma de Sugar).

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