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The login via gdm is meant to default to a face-browser allowing simple point-and-click user-selection. Only the password-entry will require the user to use the keyboard. It is still possible to type in the login-id instead of selecting the user with a mouse-click on her/his image. This will also cause the set of displayed user-faces to be filtered to the remaining completion-possibilities, thus rendering the remaining images larger and making the hit-area for a mouse-click even bigger.

In order to achieve fast and good looking transitions for this very visual login interface the use of OpenGL is mandatory.

To increase the level of integration tools like MeMaker and cheese are meant to be added to gdm-utilities like gdm-setup and gnome-about-me, so users have very easy means to provide a nice image for their entry in the face-browser.

Release Note

The default layout of the gdm-greeter uses an OpenGL-based face-browser, if the underlying graphics-hardware and driver provide the needed support, in order to provide a more pleasing login-experience. User-selection happens either by clicking on a users image/photo/face or via text-entry.


These days, with composited desktop-environments becoming more and more a standard feature, people expect their whole computing experience to be visually attractive and consistent across all parts of the system. Furthermore do we want to close the gap of visual attractiveness in the different parts of the overall desktop-experience (booting, login, desktop-usage, logout). Ideally the user should not recognize any kind of "gap" when using the computer. This attention to detail in terms of consistent look and behaviour helps give the user a more enjoyable desktop-system and improves a users confidence in the platform s/he is using.

Use Cases

The general advantage of a face-browser for login is the avoidance of superfluous typing. This helps speed up the login-procedure of all people, who are no touch-typists or experienced keyboard users. But even experienced users can enjoy the convenience of being lazy occasionally. It is still possible to login successfully without selecting an image at all just by typing in the login-name and password.

only one user on system: Although an automatic login would streamline the bootup-to-desktop cycle for a single-user system (single in terms of one real person, not "user" in terms of unix-privileges), security-concerns strongly advice against this. The single user will see only her/his photo in the face-browser.

multiple users on system (<=100): In this case a user can either just select her/his image to tell the computer their login-name or start typing the first few characters from her/his login-name and watch the face-browser filter the set of displayed images to fewer images in order to simplify locating their own image in the visible set of images.

multiple users on system (>100): Scalability-issues regarding texture-usage (especially on low-end graphics hardware) and network-latency (setups with that many users are hardly run of local harddisks) demand a fallback to a non-face-browser mode of the gdm-greeter. In that case plain text-entry widgets for login-name and password are used.

idle: When the computer is left running unattended without any user loggeded in, the gdm-greeter should switch to a screensaver-like display without locking input. Any motion of the mouse or pressed key should exit this mode. The screensaver-mode should use e.g. the user photos and make them fly round on the screen, but the user should always be able to identify that it is still the login-screen that is being displayed and not a normal screensaver from another users-session.

The threshold of a 100 users for automatic disabling the face-browser is something that needs to be properly tested during the beta-phase.


For the face-browser the OpenGL 1.3 and the following extensions will be required:

These OpenGL-limits will be required:

The recommended size for user-images is 256x256 so they will not look to blurry when scaled up. This size will have to be enforced via three means...

We currently assume that the newly rewritten gdm will be in a shippable state by the time HardyHeron enters beta. Should we forsee that this will not be the case, we will fallback to the old gdm and add the face-browser to the old version. But the work for adding a face-browser to the old gdm isn't a simple task doable in a week. There was some work done in that direction already during an earlier cycle, but it would be at least a month of work to resurrect it.


Here is the newest design superseding the old one as a mockup-movie (Ogg/Theora, no sound, just click to playback)...

Normal login procedure 1 (selecting only via mouse-click on image)...

Normal login procedure 2 (starts typing thus filtering displayed images, selects image via mouse-click when there are fewer choices). There's a username text field to know what is being typed (not on the mock-ups)

User has the caps-lock key activated...

User clicked wrong picture, needs to go back...

Examples for ~25, ~50, ~100 and ~260 faces displayed... as you can easily see with ~100 images displayed it is hard to keep an overview. People will start by typing in the first few characters of their login-id in order to filter the displayed set of images to fewer ones.

Fallback login procedure without face-browser...

Please note that these mockups are only meant to give a general idea of the look we are aiming at and to provide a basis for discussion with the artwork-team. I (MacSlow) am not part of the artwork-team itself, therefore colors, gradients, hues, drop-shadows, "roundness" etc. are just my best guesses and do not reflect the final look of the artwork. Please do not write any article about this stating something else!

The names displayed are meant to be the real names of users and not their login-ids, which are used to log in normally. For the record other OSes display real names of users too in the login-manager. Using the real name instead of the login-id, is a fair compromise between usability and security. From experience it is not too uncommon to have login-ids being rather abstract and not reflecting a users real name at all, thus displaying a users real name with their photo/image is not giving away much. Furthermore the face-browser is meant to work for local users only and not for accounts stored on LDAP or similar directory-services.

The main workload for this spec will come from the OpenGL-based face-browser. There are currently two potential candidates for becoming the rendering library of choice, pigment and clutter. At the time of this writing both lack direct support for implicit-animations and shaders. These two features will have to be added to the API of choice, once that choice has been made. Going down that path will involve a lot of additional design-discussions and work not directly related to this spec.

There is another option for providing the needed OpenGL-boilerplate. That would be to use libgtkglext as windowing-system glue and implement all needed animation- and effects-features from scratch directly via OpenGL.

Theme-support was based on a XML-file in the old gdm. This should be taken over to the new gdm.


Main libraries to be used are...

To this list either...


might be added, depding on how results of their evaluation turn out.

The evaluation process will check if the following things are available in the reviewed API...

Nearly all elements visible on the gdm-greeter screen will be multi-textured quads using fragment-shading for masking out the face-photos and other elements to get the rounded look. Some parts of the visual assets will be loaded as SVGs or PNGs from which textures will be created. This allows themeability-work by artists. Text display will be handled in a similar fashion. There the initial texture-generation is done via pango. More details will be added once the implementation has started.


Any theme and gdm-setup setting should just work with the new gdm.

During the installation of Ubuntu on a computer the user should be asked for a photo upon creation of the first account. This can either happen by offering the user a set of stock images, allow loading an image-file from an external data-source e.g. an usb-stick or web-page, take a picture with an application like cheese (if a supported webcam is found) or allow the user to create an abstract avatar-photo using a program like MeMaker. All this of course requires a lot of additional integration work that easily exceeds the scope of this spec. It would require ubiquity, Ubuntu's installer tool, to be extended with support for cheese and MeMaker.

Whenever a new user is created it has to be guaranteed, that this new user account gets a unique photo to be displayed in the face-browser. At least the fallback images need to be uniquely assigned. If the user provides her/his own photo (via webcam/cheese, avatar-maker/MeMaker or from self-provided image) we assume it to be a unique photo. To further ensure a user is able to pick the correct photo from the set of images displayed in the face-browser, their real name needs to be displayed with their photo (the login-name is used as a fallback, if no real name was provided upon user-account creation).

In order to cleanly migrate a system configuration with upto 100 users, where no user has a face-image set yet, we need to randomly assign an image from the stock image-set. Users can then afterwards still change their randomly assigned image, should they choose so. This stock image-set needs to be provided by the default installation or after an distro upgrade. The images need to be 256x256 RGB (PNG or JPG) and we need at least 100 different of them.

Test/Demo Plan

It's important that we are able to test new features, and demonstrate them to users. Use this section to describe a short plan that anybody can follow that demonstrates the feature is working. This can then be used during CD testing, and to show off after release.

This need not be added or completed until the specification is nearing beta.

Outstanding Issues

BoF agenda and discussion




DesktopTeam/Specs/GdmFaceBrowser (last edited 2009-05-29 18:29:22 by adam-w-knox)