Intent to Experiment: Multi-Screen Window Placement

[Mike Wasserman]

Contact emails

m...@chromium.org, en...@chromium.org

Explainer

https://github.com/webscreens/window-placement

Specification

https://webscreens.github.io/window-placement/

Design docs

https://web.dev/multi-screen-window-placement/

Summary

Adds new screen information APIs and makes incremental improvements to existing window placement APIs, allowing web applications to offer compelling multi-screen experiences. The existing singular window.screen offers a limited view of available screen space, and window placement functions generally clamp bounds to the current screen. This feature unlocks modern multi-screen workspaces for web applications.

Blink component

UI>Browser>WebAppInstalls

Search tags

window placement, screen enumeration, window, open, moveTo, moveBy, requestFullscreen, screen, display, monitor, multi-screen, multi-display, multi-monitor, cross-screen, cross-display, cross-monitor

TAG review

https://github.com/w3ctag/design-reviews/issues/413, https://github.com/w3ctag/design-reviews/issues/522, https://github.com/w3ctag/design-reviews/issues/602

TAG review status

Pending

Risks

Interoperability and Compatibility

Feature detection of new screen information APIs and Permission API integration allows sites to handle different levels of feature support. Existing window placement APIs generally use compatible multi-screen coordinates, but implementations often restrict bounds to the current screen. We expect low levels of risk in supporting permitted cross-screen placement requests, and falling back on legacy same-screen behavior otherwise. This work is included in the W3C Second Screen CG charter to seek consensus and support for broad interoperability: https://webscreens.github.io/cg-charter/ The Screen IDL interface duplicates EventTarget members to mark them RuntimeEnabled for this experiment, since using interface inheritance would also change the stable JS API.

Gecko: No signal We requested a position and are waiting for feedback. https://github.com/mozilla/standards-positions/issues/542 Firefox supports cross-screen window.open/move*() requests. This work partly pursues compatibility with that behavior.

WebKit: No signal We requested a position and are waiting for feedback. https://lists.webkit.org/pipermail/webkit-dev/2021-June/031903.html

Web developers: Positive (https://github.com/webscreens/window-placement/issues) Positive. This work is also of interest to Google Slides. See: https://discourse.wicg.io/t/proposal-supporting-window-placement-on-multi-screen-devices See: https://github.com/webscreens/window-placement/issues

Ergonomics

The minor improvements to window.open|move*() API behaviors have no effect on their poor ergonomics (synchronous, features string shape, etc.). This API does not preclude future work from improving the ergonomics of those existing APIs. Extending the requestFullscreen dictionary with an optional screen should pose no ergonomic risks. The new multi-screen information APIs have some minor potential ergonomics issues around naming, object comparison, and event handling that we hope to resolve using OT feedback. See https://github.com/webscreens/window-placement/issues for more details. New dual-screen and foldable screen devices are entering the consumer market, increasing the complexity of exposing reliable and actionable screen information for all device form factors. Additionally, operating systems and their window managers support different levels of screen placement APIs, and new paradigms may emerge that complicate the availability of window placement features. See the Second Screen's "Form Factors Explained" report for more explorations on these topics: https://webscreens.github.io/form-factors/

Activation

This feature incrementally extends existing screen information and window placement interfaces with basic multi-screen support. This immediately enables new compelling experiences through progressive enhancement of existing applications.

Security

Security and Privacy risks are explored in repo documents: <https://github.com/webscreens/window-placement>. That analysis and review uncovered minimal risks. Privacy concerns center around fingerprinting screen information, while security risks center around deceptive, surreptitious, or annoying window placements, such as clickjacking. Gating new functionality with a permission helps mitigate these concerns, and may aid or inspire similar protections for legacy API behavior with similar abuse vectors. The overall added risks are low and further mitigated by limiting to secure contexts, a permissions policy, providing origin-scoped generated screen ids that reset when cookies are cleared, being selective about display information to expose, and continuing to prevent off-screen window placement.

Goals for experimentation

We want developer feedback around the feature's performance and applicability in production scenarios with a broad set of screen configurations. The API shape has changed significantly since the first Origin Trial (M86-M88), and we would like to get additional developer feedback before shipping. - Does the feature permit sufficiently expressive placement requests? - Does the permission model/flow integrate well with product design? - Do any screen configurations or placement scenarios pose unforeseen challenges? At least one major customer inside Google wants to use this API in their product. We want to learn from their deployment experiences and collect metrics on feature subsets.

Reason this experiment is being extended

N/A

Ongoing technical constraints

None.

Debuggability

New and existing screen and window APIs are readily debuggable in existing developer tools.

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?

No

All Blink platforms have some support for multiple displays, but may restrict the placement and sizing of windows. The overall API will be exposed everywhere except WebView, as developers have primarily voiced interest for use cases in desktop applications, and the added complexity strongly exceeds developer enthusiasm for WebView support. All other Blink platforms will be supported.

Is this feature fully tested by web-platform-tests?

No

Flag name

--enable-blink-features=WindowPlacement

Tracking bug

https://bugs.chromium.org/p/chromium/issues/detail?id=897300

Launch bug

https://bugs.chromium.org/p/chromium/issues/detail?id=1169426

Measurement

https://chromestatus.com/metrics/feature/popularity#V8Window_GetScreens_Method

Link to entry on the Chrome Platform Status

https://www.chromestatus.com/feature/5252960583942144

Links to previous Intent discussions

Intent to prototype: https://groups.google.com/a/chromium.org/g/blink-dev/c/X6rEbWvU7cI
Intent to Experiment: https://groups.google.com/a/chromium.org/g/blink-dev/c/C6xw8i1ZIdE

This intent message was generated by Chrome Platform Status.

[Yoav Weiss]

Thanks for working on a better multi-screen experience! I know I could use that as a user :)

What's the relationship between this and the previous I2E? Has the API changed since? Any learnings from the previous trial that were incorporated into the current design?

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[Thomas Steiner]

Hi Yoav,

The API changes are documented in https://github.com/webscreens/window-placement/blob/main/CHANGES.md (and https://github.com/GoogleChrome/web.dev/pull/5591). The tl;dr is that the API shape and ergonomics have changed, based on the feedback from the first origin trial.

Cheers,

Tom

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Thomas Steiner, PhD—Developer Advocate (https://blog.tomayac.com, https://twitter.com/tomayac)

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[Mike West]

I appreciate the work y'all have done to satisfy folks from the security and privacy teams around the UX of this feature. I'm comfortable with y'all taking another stab at getting feedback from developers.

What timeline are you requesting for experimentation? M93-M95ish?

-mike

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CALgRrL%3Dnra3ZG9D4BgNz6Okye3qfcFpc6DS2FFRVZ%2BrchGWDag%40mail.gmail.com.

[Mike Wasserman]

Thanks Mike and Yoav,

Yes, M93-M95 is our target timeframe for this second OT.

As Tom said, we made nontrivial API shape (and implementation) changes to address feedback from the first OT.

See CHANGES.md, the spec PR, a slide (some of that deck is outdated), and a google-internal (for now) shape change design doc.

We want to ensure these changes satisfy partner needs and work well across a variety of OS+display configuration environments.

Let me know if you have any questions or requests. Thanks!

Mike

[Mike West]

LGTM to experiment from M93-M95.

Good luck!

-mike

[Ajay Rahatekar]

Hi All,

Due to the new Chrome 4 week cycle release cycle and the team expecting to land so CLs during the OT, can we please have approval to extend the OT by one milestone to M96? The new OT window would be M93-M96

Thanks in advance,

Ajay

[Chris Harrelson]

Sure thing. LGTM

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/3a08c6c0-7fce-42b0-bbd9-b910f1c9dc46n%40chromium.org.

[Ajay Rahatekar]

Ty, Chris.

[Thomas Schaaf]

Hello,

right now it's not possible to register for the experiment anymore. Would it be possible to open registration again? Or will the feature be changed so that it is available behind a feature flag?

Thomas

[Mike Wasserman]

[BCC blink-dev]

Hi, Thanks for reaching out. The Origin Trial has ended, but developers can still test these features.

• Either enable: chrome://flags/#enable-experimental-web-platform-features
• Or run chrome with the command line flag: --enable-blink-features=WindowPlacement

Feel free to submit issues on GitHub and watch ChromeStatus for status updates.

Thanks,

Mike