The final report

August 19, 2012

So, the hard-pencils-down date is now just around the corner, and there were only a few small things left to be done.

Nothing radical happened since the last report just a few days ago. A couple of you left some comments that I haven’t yet had time to get to, but I sure will, hopefully soon.

The code for the GNOME Settings Daemon plugin and GNOME Control Center panel was refined a bit and documented where I felt it was required, and pushed into the GitHub forks (GSDGCC) I’ve been using during this period. To mark the end point of the GSoC coding period I’ve created the GSOC_PENCILS_DOWN tags in both repositories (GSDGCC) – there might still be some commits due to the merging of both components into their corresponding repositories at Two bugs were created to cover that effort, one for the GSD plugin and another for the GCC panel.

The design proposal was also updated to reflect the latest intention of the panel functionality. The design itself will most likely be quite important when merging the panel into the main trunk and enabling it.

Keeping it short this time, and covering pretty much everything I had in mind. You’re welcome to check out the project page to see more about how I spent this summer. But do note that the timeline there was at the end not really followed as closely as one would like.


The GSoC period is swiftly coming to its end, with the ‘soft pencils-down’ date already passed. While I’m not yet completely finished with my project I am very close, though, with only some small bits of functionality left to implement and with a quick walk through all the code to sort out the code styling issues and possible memory leaks.

What’s new

Quite some time has passed since the last report and the work has progressed quite a lot in that time. The Gamepad API support in WebKitGTK+ was already complete and pretty polished so the only thing remaining was the implementation of the GNOME Settings Daemon plugin and GNOME System Settings panel. The former’s task would be to recognize supported devices as they are connected and apply to them the correct buttons and axes mappings and previously-stored calibration data. The latter would be used by the users to see if their device is supported and, if the device was well enough supported by the Linux kernel itself, the user could calibrate the device him- or herself.

What changed from the original idea

The most significant change is that originally, I was thinking of giving the users the complete control over the buttons and axes mappings. That would mean that each user would go through an annoying and long process of manually configuring the device. But such processes immediately require the user to understand more about his device and the general gamepad/joystick button and axis layout than it is either required or productive for everyday life. Rather than that the decision was made to spare the user all the hassle around the configuration and rather use preset buttons and axes mappings for specific devices.

This would of course mean that some users might connect a device that the system does not yet recognize as supported. The user could still interact with the device (the system would not block the device’s usage) but could also request that device is awarded the supported status with appropriate mappings assigned to its unique ID. Rather than waiting 6 months for the new release, the data about all the supported devices is stored on the Web and is cached locally and updated whenever a new device is given the supported status and the list of supported devices is expanded. While the Web-located list of supported devices is already working well in the current daemon plugin, the ‘support request’ is, at this moment, only an idea that needs more discussion about approach and implementation.

The internals

The GNOME Settings Daemon plugin was already described in quite some detail. The update of the supported devices list is done when a mismatch in the checksums of the local and Web-located list occurs. The checksums are compared when the daemon starts, and that’s normally when the session begins (at login). ┬áThe devices list is written in JSON, so the plugin uses JSON-GLib to parse the list. The device is updated with proper mappings and current calibration through the Linux kernel driver. As much as convenient, these drivers are not quite the holy grail, but more on this later.

The GNOME System Settings panel, as already told, shows the connected devices, their support status, and provides calibration dialog if the device can handle it. The current design is my own, so it’s nothing extra (hopefully in either extreme, good or bad :>), but it has the functionality that it should provide. Here are the two screenshots, first shows the device listing, the second the calibration dialog.

What’s left

The functionality of both the GNOME Settings Daemon plugin and the GNOME System Settings panel is there, all that remains to do in the time left in the GSoC period (three days :>) is to polish the code, document it and start the effort of merging back into the main repositories. The work was done in the mirror repositories I’ve set up on GitHub (the project page has more info on this), with all the work contained in the master branches.

I’ll open two separate bugs for each project in which I’ll upload the merge patches up for review. My mentor Carlos has already volunteered to do some reviewing while the two projects’ maintainers will have a thorough look as well, of course. The design proposal will be updated as well, based on the current panel design. GNOME designers will be invited to have a look, comment on the various approaches and present any design ideas in sketch form.

Hopefully, with a proper design and a couple of devices being supported, the maintainers will give the thumbs-up to enable both the daemon plugin and the control panel in trunk, so they’d make it into GNOME 3.6. If not, there will be enough time to polish both components to near-perfection for the 3.8 release. And talking of polishing things, the device drivers in the Linux kernel need some of that too.

The devices agony

Truth be told, this is partly a rant. And it’s only based on two devices that don’t work properly. I’ve invested into a Wii Remote and a Sony Playstation DualShock3 gamepad to see how they behave with GNOME. They’re both Bluetooth devices, with the DualShock being also connectable through a mini USB cable. Unfortunately, while I’ve had to put quite some effort into connecting the Wiimote, the DualShock stayed reluctant to connect via Bluetooth. But even when connected, the Wiimote wasn’t presented well as a joystick device (the /dev/input/js* file was there, but pretty much useless), neither was the accelerometer propagated as such through GUdev.

The DualShock, when connected through the USB cable, was picked up as a joystick device by the joydev driver, the generic joystick device driver in the kernel. But you’d think it’s quite a special device when it popped out with 27 axes and (if I remember correctly) 18 buttons. A normal gamepad has 6 axes (two of those are the D-pads) and 12 buttons. The DualShock has these neat pressure-sensitive buttons, but the sensor data is exposed as an axis instead of the button value being regulated between 0 and 1 based on that pressure. Also exported as device axes is the accelerometer data, which could (well, should) be exposed as what it is – an accelerometer. There are also a couple of axes that I wasn’t able to locate at all, so I guess that’s sort of a bonus.

While the inability to connect via Bluetooth probably falls under Bluez, it’s obvious DualShock should have a custom driver to handle all its features. There’s a Wiimote-specific driver but I’m not entirely sure of its status in the Linux 3.2 kernel (used when testing), this driver looks OK in Git master, exporting accelerometer data as well, but I haven’t had time yet to test it properly. The Xbox controllers have a specific driver, so they should work in theory but I haven’t tested them really (well, I should buy one first). But it’s the DualShock annoyance that bothers me the most, the device is expensive and advanced as well, but with the current support it turns out to be nothing more than a toy. The device driver wasn’t a planned goal of this GSoC project but it might as well be a late collateral damage.


This blog post has gotten a bit lengthy, so let’s end it. I’ll post another, final report on Sunday just to explain what was left undone and what was actually completed, along with the status of the merge, and where this project could still improve outside of the GSoC scope.