Use cases and requirements for Presentation API

This document captures the use cases and requirements to consider in the specification of the W3C Presentation API.

Use Cases

This section collects relevant use cases for the Presentation API.

Each use case is defined in its own subsection. To define a new use case just copy/paste an existing one and update the use case identifier (UCxx), title, description and requirements.

UC01: Presentation

A user is preparing a set of slides for a talk. Using a Web-based service, she edits 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. At the conference, using wireless display technology, she presents 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 stage screen shows her slides to the audience. At the end of the presentaton, she clicks a button to stop presentation, which stops showing slides on the stage screen and reverts to a local view of the presentation on her mobile phone.

Requirements: REQ01, REQ02, REQ05, REQ06, REQ09

UC02: Video and image sharing

Using an online video or image sharing service, a user would like to show memorable moments to her friends. However, she cannot show the content to a large group of people using her smartphone with its small screen. She connects an external TV screen to her mobile device (wired or wirelessly); the online sharing service now makes use of the connected display, allowing a wider audience to enjoy the content. After the connection is made, the Web page adds a button (e.g., "send to second screen") that allows her to send content to the TV screen.

She clicks the "send to second screen" button to start display on her TV screen, then selects a set of videos and images to show there. The playback starts on the TV screen and continues even after she navigates to another Web page on her mobile device. She navigates back to the online sharing service and the site reconnects automatically to the content shown on the TV screen.

Requirements: REQ01, REQ02, REQ03, REQ05, REQ06

UC03: Multiplayer gaming - Poker

Bob enters an online poker site on his smartphone to play poker with friends. He selects the option "create new game" to start a game session for two players. The poker site detects that there is display available and asks Bob to extend the game UI by keeping his personal cards and control UI on the smartphone and displaying the poker table on the large display. Bob confirms and waits for other players to join.

Alice is visiting Bob and decides to join the game. She opens the same poker site in the browser on her smartphone and selects the option "join game". The browser shows a dialog with a list of running poker sessions. She selects the session started by Bob and joins the game. The game starts immediately after two players are joined. Now Alice and Bob can see their personal cards on their smartphones and the large screen displays the poker table with shared cards, current bets, and remaining money of each player.

Requirements: REQ01, REQ02, REQ04, REQ05, REQ06, REQ07

Images

Poker Table
Poker Player: Alice
Poker Player: Bob

UC04: Media flinging to multiple screens

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".

Requirements: REQ01, REQ02, REQ05, REQ06, REQ08

ISSUE #40: Screen availability mechanism for multiple sessions

UC05: Multiplayer gaming - Pictionary

Bob visits a Pictionary game [PICTIONARYGAME] site on his smartphone. He clicks the "Start on TV" button and selects his TV’s name from the list of presentation displays that pops up on the phone's screen. The Pictionary site opens on the TV screen.

Bob now waits for Ann and Joe to join the game from their smartphones by opening the same site and connecting to the TV. After all the players have joined, Bob presses the "start game" button on his smartphone and receives the first word to draw: "blanket."

Bob draws a picture of a blanket on the touch screen of his smartphone. The picture is mirrored on the TV screen as he draws. At the same time, Ann and Joe are trying to guess what Bob is drawing by typing answers on their own smartphones and sending them to the TV screen. The TV shows the answers coming from all users and the game continues until Ann provides the correct answer. Ann gets points for the correct answer. The next round of the game starts with Ann drawing a new word.

Joe then decides to exit the game by pressing the "exit game" button. That information is passed to the TV and Joe's name disappears from the list of the players on the TV screen. Bob and Ann play one more round of the game with Ann drawing and Bob guessing the correct word. After that round is over, they decide to stop playing and both press the "exit game" button on their smartphones. The site on the TV is notified that all the players have left the game, and it presents a list of the top players. No one decides to start a new game, and after a period of time the the game on the TV exits itself.

Requirements: REQ01, REQ02, REQ04, REQ05, REQ06, REQ07, REQ09

UC06: Presenting to local and remote screens

Alice enters a conference room with two flat screen TVs. She opens a slide presentation site and initiates presentation of a deck of slides on the first TV. The presentation connects automatically to the second TV to show a video accompanying her slides.

Alice wishes to present simultaneously to Bob, who at a remote site. She initiates a connection via the presentation site to Bob's conference room, which causes the presentation running in Alice's room to start showing on the TVs in Bob's room. As Alice moves through the slides in her room, the content in Bob's room remains in sync.

When Alice is done presenting, she stops presentation locally, which also terminates presentation on Bob's TVs.

Requirements: REQ01, REQ02, REQ04, REQ05, REQ06, REQ07

Requirements

This section collects all requirements derived from the use cases listed in the previews section.

Each requirement is defined in its own subsection. To define a new requirement just copy/paste an existing one and update the identifier (REQxx), title and description.

REQ01: Discovery & availability

The UA must provide a way to find out whether at least one presentation display is available.

REQ02: Launching presentation

The UA must provide a way to start sending content to a presentation display or displays from a controlling browsing context (or controller), which creates a new receiving browsing context (or presentation). 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.

REQ03: Resuming connection to presentation

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).

REQ04: Joining presentation

The UA on the controller device must provide a way for controlling browsing context to join running presentations. These are started in general either manually by the user or from another controller as described in REQ02.

REQ05: Communication

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.

REQ06: Signaling disconnection

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.

REQ07: Multiple controllers per presentation

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.

REQ08: Multiple presentations per controller

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.

REQ09: Terminating presentation

A connected controller should be able to request termination of a presentation, which closes the browsing context and disconnects all connected controllers. In addition, a presentation should be able to terminate itself.

Non-functional Requirements

NF-REQ01: Power saving friendly

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.

References

[PICTIONARYGAME] https://en.wikipedia.org/wiki/Pictionary

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