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Merge in new use cases.
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mfoltzgoogle committed Jun 1, 2015
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table thead, table tbody { border-bottom: solid; }
table td, table th { border-left: solid; border-right: solid; border-bottom: solid thin; vertical-align: top; padding: 0.2em; }
dfn { font-weight: bolder; font-style: normal; }
#use-cases-and-requirements dd { margin-top: 0.5em; margin-bottom: 1em; }
.copyright { font-size: small; }
</style>
</head>
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<h2>
Use cases and requirements
</h2>
<section id="use-cases">
<h3>
Use cases
</h3>
<dl>
<dt>
Presentations
</dt>
<dd>
A user is preparing a set of slides for a talk. Using a web-based
service, she is editing her slides and speaker notes on the primary
screen while the secondary larger screen shows a preview of the
current slide. When the slides are done, her mobile phone allows
her to access them from an online service while on the go. Coming
to the conference, using wireless display technology, she would
like to present her slides on the stage screen from her mobile
phone. The phone's touch screen helps her to navigate slides and
presents a slide preview while the projector shows her slides to
the audience.
</dd>
<dt>
Video and image sharing
</dt>
<dd>
Using an online video or image sharing service, a user would like
to show memorable moments to her friends. Using a device with a
small screen, however, a user cannot show the content to a large
group of people. Connecting an external TV screen or projector to
her device - with a cable or wirelessly - the online sharing
service now makes use of the connected display, allowing a wider
audience to enjoy the content. The web page shows UI elements that
allow the user to trigger displaying content on the secondary
display (e.g., a "send to second screen" ) only if there is at
least one presentation display available.
</dd>
<dt>
Multiplayer gaming
</dt>
<dd>
Splitting the gaming experience into a near screen controller and a
large screen visual experience can create new gaming experiences.
Accessing the local display on the small screen device and an
external larger display allows for richer web-based gaming
experiences.
<p class="open-issue">
<a href="https://github.com/w3c/presentation-api/issues/27">ISSUE
27: Define a multiplayer gaming use case</a>
</p>
</dd>
<dt>
Media flinging to multiple screens
</dt>
<dd>
Alice enters a video sharing site using a browser on her tablet.
Next, Alice picks her favorite video from the site, and the video
starts to play on her tablet. While the video is playing Alice
clicks a button "Share on different screen". The browser provides a
user interface that lists all the screens Alice has at her home,
asking her to select one. The screens are identified by names that
are familiar to Alice. Alice picks one screen from the list,
"Alice's big TV", and the video playback continues seamlessly on
the selected screen. Next she decides to switch the playback to a
different screen. She clicks the same button "Share on different
screen" provided by the site, and the browser presents the user
interface that lists all the screens. Alice picks another screen
from the list, "Alice's kitchen TV", and the playback resumes on
that screen. Video site also provides a feature to see the action
(Alice is watching a soccer game) from a different angle. Alice
clicks a button "Select screen for additional angle", and the
browser asks Alice similarly to select the screen for playback.
Alice picks "Alice's Projector" and the soccer game is shown on the
projector from a different angle, in parallel to the content being
played back on "Alice's kitchen TV".
<p class="open-issue">
<a href="https://github.com/w3c/presentation-api/issues/40">ISSUE
40: Screen availability mechanism for multiple sessions</a>
</p>
</dd>
</dl>
</section>
<section id="requirements">
<h3>
Requirements
</h3>
<p>
The requirements enumerated in this section are derived from the
<a href="#use-cases">use cases</a>.
</p>
<section>
<h4>
Functional requirements
</h4>
<dl>
<dt>
Discovery &amp; availability
</dt>
<dd>
The UA must provide a way to find out whether at least one
<a href="#presentation-display">presentation display</a> is
available.
</dd>
<dt>
Launching presentation
</dt>
<dd>
The UA must provide a way to start sending content to a
presentation display or displays from a <span>controlling
browsing context</span> (or <em>controller</em>), which creates a
new <span>presenting browsing context</span> (or
<em>presentation</em>). This may occur at the request of the
controller or at the request of the UA. A single controller may
be able to send content to multiple displays at once, and a
single display may be able to host multiple presentations at
once.
</dd>
<dt>
Resuming presentation
</dt>
<dd>
If a controller becomes disconnected from its presentation, the
UA must provide a way for it to resume its connection to the
presentation. It must also provide a way for a new browsing
context on the same UA to request connection to one or more
presentations (thus becoming their controller).
</dd>
<dt>
Communication
</dt>
<dd>
The UA must enable exchange of data between a presentation and
its controller or controllers. This data exchange can be used to
determine what content is shown in the presentation. The UAs that
host the controllers must not make an assumption about the
execution locality of the UA that hosts the presentation; they
may be rendered on one or more remote UAs, and thus the
communication channels between a presentation and its controllers
is loosely coupled.
</dd>
<dt>
Signaling disconnection
</dt>
<dd>
The UA must signal disconnection between a controller and a
presentation to both the controller and the presentation. The
controller or the presentation may choose to initiate
disconnection; in that case, the UA must signal disconnection to
the other side.
</dd>
<dt>
Multiple controllers per presentation
</dt>
<dd>
A presentation should be able to accept control (via data
exchange) from multiple controllers simultaneously. Not all
presentations will support this; for example, when the
presentation browsing context is not accessible to other devices.
</dd>
<dt>
Multiple presentations per controller
</dt>
<dd>
A single controller should be able to launch multiple
presentations and exchange data with them. Each connection
between a controller and a presentation is handled independently
by the UA; controlling the same content on multiple presentations
simultaneously in a synchronized fashion is out of scope for this
specification.
</dd>
</dl>
</section>
<section>
<h4>
Non-functional requirements
</h4>
<dl>
<dt>
Power saving friendly
</dt>
<dd>
All API design decisions must be analyzed from a power efficiency
point of view. Especially when using wireless display
technologies or querying availability over a radio channel, care
needs to be taken to design the API in a way that does not pose
obstacles to using radio resources in an efficient way. For
example, powering up the wireless display detection only when
needed.
</dd>
</dl>
</section>
</section>
Use cases and requirements are captured in the
separate <a href="https://github.com/w3c/presentation-api/blob/gh-pages/uc-req.md">Presentation
API Use Cases and Requirements</a> document.
</section>
<section>
<h2>
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</tbody>
</table>
<p>
In order to satisfy the <span title=
"non-functional-requirements">power saving non-functionional
requirements</span> the user agent must keep track of the number of
In order to satisfy
the <a href="https://github.com/w3c/presentation-api/blob/gh-pages/uc-req.md#req08-power-saving-friendly">power saving non-functional requirement</a>, the user agent must keep
track of the number of
<code>EventHandler</code>s registered to the
<code>onavailablechange</code> event. Using this information,
implementation specific discovery of <span title=
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