cananian

Chris Ball has done an excellent job posting video from all the talks at EduJam in Montevideo. I gave talks on Sugar, Education, and Tablets, The Diamond Age, Internationalization Everywhere, and Sugar on Android and Native Client.

I've reached the end of the month. I've accomplished my Android and NativeClient-related goals, but didn't get the time to do as much mesh and python investigation as I'd wanted. Here are some ideas for next month's work. (Next week I'll be in Uruguay for EduJAM.)

GObject Introspection (Android or NaCl)

1. Start by porting libffi. An android port would be straightforward, but since libffi involves code generation (ARM, x86), this is going to require a bit of assembly magic and the new "JIT"/"shared library" support in the NaCl plugin.
2. Then port gobject-introspection. GObject-Introspection relies on libffi for its guts, but the hard part of this port will be refactoring g-i's build process, which is not cross-compilation friendly. Might need to rewrite some tools. If targeting NaCl, you might consider finishing the code allowing execution of unsandboxed NaCl binaries.
3. Turn gobject-introspection on its head: generate GIR and a C binding for the platform "native" interface. For NaCl, this would be a GObject-using C-level binding of the browser-native DOM; for Android, this would be a GIR binding of the native Android APIs. These bindings should be mostly automatically generated, since they will need to continue tracking successive native platform releases/HTML5 features.
4. Demos! Change browser DOM from Python, write native Android apps in Python. Add a gobject-introspection binding to cforth, then do the same from forth. (Forth might be a simpler place to start than Python. Or not.)

GTK (Android or NaCl)

1. Build on the cairo/pango port to proceed to a full GTK backend for Android/NaCl. These backends ought to be upstreamable. The NaCl port should be based on the broadway work: the cairo canvas would be drawn to more directly, but a lot of the mechanism which captures JavaScript events and translates them into the GTK event loop could probably be reused.
2. Demo: "Hello GTK world" in Android/NaCl.

Sugar partitioning.

Bring Sugar closer to being a true multi-language multi-library platform.

1. Refactor sugar modules (for example, sugar toolbar widget) as standalone C libraries. Basic idea is to embed Python and export a C API, while preserving as much of the code as possible. Python libraries now invoke this library via g-i-r instead of directly. The python embedding tool is probably a useful standalone product.
2. Rewrite "Hello, Sugar" activity in C (or vala), using #include for import and GObject inheritance instead of python inheritance. Use this as a guide to pull apart sugar into modules (as above) to make this code actually work as written.

Miscellanous topics

1. ChromeOS w/ touch support.

   Find an appropriate machine, do an installation, what are the roadblocks/rough spots? Can we install on XO-1.75 as a testbed?

2. TurtleArt as JavaScript viewer/editor.

   Revisit TurtleScript work, but skip over the time-consuming "construct an editor" step by reusing the (excellent) TurtleArt code.

3. Mesh: android olsrd frontend, build testbed, research 802.11 DCF issues.

Summary

There are four rough topics here; I might try to continue the breadth-first search by spending a week on each. It might be more satisfying to downselect two of these issues and spend two weeks on each.

At the end of my Sugar/Android week, I had a simple Pango-on-Cairo demo running. This was built on a stack of ported libraries, including gettext, pixman, freetype, libxml2, fontconfig, and glib, as well as cairo and pango. You can run the demo yourself by sideloading pango-demo.apk onto your Android device (tested on a Motorola Xoom), and you can browse the source code to see what it entailed (here's the scariest part). (I was inspired by Akita Noek's android-cairo project, but I ended up reworking the build scheme and redoing most of the ports.)

It made sense to start my Sugar/NaCl investigation by porting the same demo application to Native Client. The same stack of ported libraries was involved, although it was easy to include more functionality in the Native Client ports, including threading and PNG/PS/PDF support in cairo. The source code is a fork from the upstream naclports project, and the process was generally much cleaner. (But see my previous post for some caveats regarding naclports.) If you're using Chrome 10 or 11, you can run the demo in your browser (follow the instructions on that page). The Wesnoth team has a parallel project which ported some of these libraries as well, but not in an upstreamable manner.

The demo app uses cairo to draw the background, an animated X, and some basic text in the center; it uses Pango's advanced international text support to draw properly-shaped Persian text in a circle around it. The center text is the "proper" bilingual Greek/Japanese written form of "pango"; the text around the edges is the Persian name of the internationalization library, "harfbuzz". Note that the Persian text is written right-to-left—and that I didn't put a full CJK font in the NaCl app, so the Japanese "go" character is missing. The Android port rebuilds the font cache at each startup, so it loads rather slowly; the NaCl port contains a prebuilt font cache so it starts more quickly.

Both ports took about two weeks. I blew my original schedule, partly due to the Patriot's day holiday, and partly because I'd given Android about a week's head start by tinkering on it before my original schedule post. The framerate of the demo is much better on NaCl (so fast that the edges of the animated X look choppy in the screenshot), but the hardware isn't easily comparable, so the comparison doesn't really tell us much. The porting effort was certainly more pleasant on NaCl, since newlib is a much more complete libc than Android's "Bionic"—but having gdb available made debugging on Android easier. (There is an unintegrated NaCl branch that integrates NaCl gdb in the browser, though!)

Much of the GNOME/POSIX library stack assumes access to a filesystem tree and does file-based configuration. In our demo application, fontconfig was the most culpable party: it wanted to load a configuration file describing font locations and naming, then to load the fonts themselves from the file system, and finally to write a cache file describing what it found back to the file system. Most ported software is going to want similar access—even if you store the user's own documents in a Journal, software still expects to find configuration, caches, and other data in a filesystem.

Android provides the POSIX filesystem APIs, but the filesystem an app can touch is segmented and sandboxed. As discussed previously, Android's Opaque Binary Blob feature may allow you to create a app-specific filesystem, but this doesn't let you share (for example) fonts and font configuration between activities. NaCl might eventually provide a similar unshared mechanism based on the HTML5 AppCache.

The preferred solution is more limited, but more flexible: no built-in filesystem APIs are used (or in NaCl's case, provided!) at all. Instead, you provide your own implementation of the POSIX file APIs (either via the --wrap linker indirection or through an appropriate backend to newlib/glibc/glib). For the NaCl demo app, I wrote a rather-elaborate in-memory filesystem --- only to find that an even-more-elaborate one already existed in naclports. But the longer-term solution uses message-passing (SRPC in NaCl, intents in Android) to implement these POSIX APIs. In Native Client, the implementation would be in browser-side JavaScript, which would then allow you to share parts of the filesystem tree between activities and/or map it into (cached) web-addressed resources. In either case, your application still sees the bog-standard POSIX API it expects.

More problematic are the networking APIs. Here Android provides a pretty standard socket library, while Native Client provides nothing at all. Using a browser-based implementation, as for the file APIs, will work fine for HTTP, WebSockets and even P2P via the HTML5 P2P APIs. But it's not clear that (for example) glib's elaborate asynchronous DNS name resolver implementation can (or should!) be implemented in a NaCl port.

In the end, the porting effort and abstraction shifts needed for Native Client and Android are roughly comparable. I expect Native Client will hold a strong edge in allowing close integration with web standards and web technologies. Android will probably continue to hold an edge in third-party application support and platform maturity.

This post will describe the state of Native Client in general, based on week 2 of my original four week plan. In the next post, I'll link to my work so far, and compare the Native Client and the Android efforts. Recapping, the end goal of these explorations is a platform for the next generation of the Sugar learning environment.

To begin, the Native Client (NaCl) plugin is fairly mature in a number of areas. Version 0.2 of the NaCl SDK was recently released (a version number which substantiates the "fairly" in my previous sentence), and the NativeClient plugin is currently shipping in Chrome (versions 10 and 11), although you have to manually turn on a preference in the about:flags dialog to enable it. The NaCl toolchain is much more standard than the Android NDK toolchain I discussed previously, and the robust naclports tree shows that the patches required for NaCl ports of common packages tend not to be too evil. The Tcl interpreter and Qt tookit port demos show that fairly complex pieces of code can be deployed today on NaCl.

On the other hand, there are three main difficulties:

1. The default NaCl toolchain uses newlib as its standard C library. This is consistent with Google's preference for BSD-licensed code in SDKs they provide to the public (see the discussion of Bionic in the Android SDK). However, there also exists a branch of the SDK which uses glibc. The glibc branch supports several additional features, like shared library support. However, it is unclear whether this will ever be a "supported" part of the SDK. If glibc does become supported, it is unlikely ever to be the only supported libc; the BSD-licensed newlib will need to remain available as an option. (Yes, the LGPL license of glibc shouldn't inspire such paranoia, but Google has elected not to undertake the education of all prospective third-party developers.)
2. The naclports project, although fairly robust, is driven between the Scylla and Charybdis of compatibility. The goal is that all the code in naclports be buildable at all times on all three major platforms: Windows, Mac, and Linux. Further, it should support both x86_32 and x86_64 backends, and ideally ARM and pNaCl as well. It's auto-built against the latest SDK sources, but should also work on the latest released SDK. And with the addition of the glibc/newlib split discussed above, the possible build targets are multiplied further. Needless to say, keeping the tree building against such a large number of variants is not an easy task, and naclports is usually broken in some way. In practice, most developers seem to pay attention to some subset (say, x86_32/newlib/Linux host), but it's hard to push patches upstream without worrying about breaking some obscure target. It might be best to base future work on a proper package technology, like (say) dpkg-cross.
3. In general, a lot of interesting NaCl development has occurred on branches that are not easily integrated. I've already mentioned glibc support, which is a toolchain branch; shared library support is on another branch that requires a new chromium plugin as well. At various times different means have been implemented to run NaCl binaries "natively" outside the sandbox (for example, in order to test some feature at build time, or auto-generate some piece of code via introspection). These efforts live on abandoned branches, while the "official" means to do this is incomplete. Similarly, a lot of interesting NaCl work used the now-abandoned legacy "NPAPI" plugin interface to interact with the browser. It was followed by the "Pepper" plugin interface, which was itself abandoned. Current work uses the Pepper2 browser plugin APIs, which (unfortunately) have not yet been implemented in non-Chrome browsers and continue to flux about. Many interesting browser interactions exist only in deprecated Pepper APIs, not having yet been built into Pepper2. ARM and pNaCl work also appears to be on unintegrated branches. There are a number of different gdb support strategies.

None of these difficulties is insurmountable—and in fact, some are side-effects of the desirable active development and productization of Native Client. To date I've done my work on the (more compatible) SDK v0.1 and the (more upstreamable) newlib library. So far newlib has not been a huge obstacle, and this basis allows my patches and ports to be more broadly useful. This might change in the future—certainly at some point we need to move to ARM and/or pNaCl for XO-3, which will probably require building chrome and the NaCl toolchain from scratch. At that point, it may be worth further exploring the non-mainstream branches.

Last Monday I rejoined One Laptop Per Child as Director, New Technologies. My mandate is hardware and software for the XO-3, OLPC's upcoming ARM-based tablet computer for education in the developing world. The new machine should be lower cost, lower power, more indestructible, more powerful, and potentially more expandable than ever. There are about two million machines in the XO-1 family (XO-1, XO-1.5) in the hands of kids today. The XO-3 will build upon this impressive foundation to reach further into the poorest and least-connected regions of the world.

I will kick-off my work with a series of four week-long sprints between now and eduJAM Uruguay to investigate a number of possible directions for the educational software stack on the XO-3 tablet. On the XO-1—series machines OLPC ships Sugar, an impressive collection of educational software developed by Sugar Labs. How can we best keep the best of Sugar while yanking the UI forward into a touch-friendly tablet world?

1. This week (April 4-8) I'll begin by working on a port of the GTK3 UI library to Android. The GTK3 library contains touch support missing from the GTK2 library on which Sugar is currently based. The end goal here would be a full port of the Python/GTK-based Sugar APIs, running on something like the Honeycomb Android OS. Our existing educational activities could be ported to the new APIs without too much difficulty, but we'd largely use the existing Android OS facilities instead of the parts of Sugar concerned with low-level system management. To clarify: this is a preliminary exploration—we haven't decided to base the tablet software on Android (or anything else) yet.
2. The next week brings a new direction. During the week of April 11-15 I will start porting Python/GTK3 to Chrome or ChromeOS via the Google NativeClient plugin. This path would result in activities which more fully integrate with web technologies—even in disconnected regions of the world. On desktop machines, Sugar activities could be run inside the Chrome browser, while ChromeOS (or another embedded OS running chrome/webkit) would provide the system management functions on tablet machines like the XO-3. As with the Android port, this is an exploration, not a definite software direction.
3. The week of April 18-22 I hope to focus on mesh networking. This has a somewhat checkered history in our deployments; I hope to identify the remaining roadblocks and map a way forward to make this a flagship feature of the XO-3 software.
4. The week of April 25-29 is for the existing Python-based Sugar codebase. In order to continue moving forward, it needs to migrate to GTK3, gobject-introspection, and some other key enabling technologies. I believe it would also benefit from language-independent APIs and better modularization to allow a more incremental migration path.

The following week is Conozco Uruguay and the Uruguay EduJAM where I'll present my progress on these initial exploratory projects and discuss the path ahead with the wider OLPC and Sugar communities. Clearly, a week each is not enough time to finish any of these projects! But the focused effort should help to better identify the promise, roadblocks, and challenges in each of these paths, which then in turn will help us to plan the future.