Intent to Ship: New TextMetrics API in Canvas

[Yi Xu]

Contact emails

yi...@chromium.org, fs...@chromium.org

Spec

https://html.spec.whatwg.org/multipage/canvas.html#textmetrics

we are launching the following attributes in TextMetrics: actualBoundingBoxLeft, actualBoundingBoxRight, fontBoundingBoxAscent, fontBoundingBoxDescent, actualBoundingBoxAscent, actualBoundingBoxDescent, emHeightAscent and emHeightDescent.

TAG Review:

https://github.com/w3ctag/design-reviews/issues/302

Summary

this is 2nd attempt to ship TextMetrics (first attempt link). The current canvas TextMetrics API only exposes the width of the measured text. Part of the new API was already implemented under a flag, but there were some inconsistencies and bugs, especially with RightToLeft text.

The feature bug (https://crbug.com/277215) has strong user support (24 stars, 3 more stars since Sept 2018).

Link to “Intent to Implement” blink-dev discussion

https://groups.google.com/a/chromium.org/forum/?fromgroups#!searchin/blink-dev/textmetrics|sort:date/blink-dev/SgofW_bQ3ps/jNYamQHplAMJ

The thread was titled “Intend to ship”, but it was seen as “Intend to implement” and was never actually shipped.

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

Yes

Demo link

-

Debuggability

No DevTools needed for debug. Users can console print the full TextMetrics object in one line.

Risks

Interoperability and Compatibility

Safari already has already shipped these metrics following this spec. Firefox started development 4 years ago but never shipped

Firefox: In development

Safari: Shipped

We know this is a major feature requested by developers (as well as internal Google teams like Google Docs). This API will help developers have more control and more accurate text rendering. As of today a different way to achieve this is by using rendering text to the DOM and using getBoundingClientRect to get some measurements. This process requires a relayout of the page.

Activation

Enable the platform experiment ExtendedTextMetrics

Is this feature fully tested by web-platform-tests? Link to test suite results from wpt.fyi.

A set of test for each metric, prefixed by “2d.text.measure”:

https://wpt.fyi/results/2dcontext/drawing-text-to-the-canvas

Entry on the feature dashboard

https://www.chromestatus.com/feature/5307344997056512

[Philip Jägenstedt]

It looks like the TAG review on this was brief because part of the API was reverted in the spec. +L. David Baron filed 4 spec issues as part of that review, which remain open:

https://github.com/whatwg/html/issues/4070

https://github.com/whatwg/html/issues/4071

https://github.com/whatwg/html/issues/4072

https://github.com/whatwg/html/issues/4073

I haven't studied the issues, but are any of them relevant to the subset of this API that you're proposing to ship? If so, can those issues be settled first?

+Domenic Denicola 

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[oj...@google.com]

Clarification: Regarding the "In development" for Mozilla, that bug looks like it hasn't gotten attention in 9 months, so it's probably not being actively worked on unless you have some other signal that it is. That does imply at least that there isn't significant opposition though. :)

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[Yi Xu]

The open bugs are related to some description used on specs, it doesn't change the behavior of the implementation. 

[L. David Baron]

I don't think that's quite right:

#4070 is suggesting that perhaps the APIs should be renamed
(although it seems like maybe there's consensus that the current
names are OK)

#4073 might also result in substantive behavioral changes; I
initially thought the issue was editorial, but given that the
response was that the text was as intended means that there are now
substantive questions of implementation behavior.

-David

On Monday 2019-06-10 15:34 -0400, Yi Xu wrote:
> The open bugs are related to some description used on specs, it doesn't
> change the behavior of the implementation.
>
> On Thu, Jun 6, 2019 at 3:31 PM <oj...@google.com> wrote:
>
> > Clarification: Regarding the "In development" for Mozilla, that bug looks
> > like it hasn't gotten attention in 9 months, so it's probably not being
> > actively worked on unless you have some other signal that it is. That does
> > imply at least that there isn't significant opposition though. :)
> >
> > On Monday, June 3, 2019 at 2:45:03 AM UTC-7, Philip Jägenstedt wrote:
> >>
> >> It looks like the TAG review

> >> <https://github.com/w3ctag/design-reviews/issues/302> on this was brief

> >> because part of the API was reverted

> >> <https://github.com/whatwg/html/pull/4037> in the spec. +L. David Baron filed

> >> 4 spec issues as part of that review, which remain open:
> >> https://github.com/whatwg/html/issues/4070
> >> https://github.com/whatwg/html/issues/4071
> >> https://github.com/whatwg/html/issues/4072
> >> https://github.com/whatwg/html/issues/4073
> >>
> >> I haven't studied the issues, but are any of them relevant to the subset
> >> of this API that you're proposing to ship? If so, can those issues be
> >> settled first?
> >>
> >> +Domenic Denicola
> >>
> >> On Fri, May 31, 2019 at 7:14 PM Yi Xu <yi...@chromium.org> wrote:
> >>
> >>> Contact emails
> >>>
> >>> yi...@chromium.org, fs...@chromium.org
> >>>
> >>> Spec
> >>>
> >>> https://html.spec.whatwg.org/multipage/canvas.html#textmetrics
> >>>
> >>> we are launching the following attributes in TextMetrics:
> >>> actualBoundingBoxLeft, actualBoundingBoxRight, fontBoundingBoxAscent,
> >>> fontBoundingBoxDescent, actualBoundingBoxAscent, actualBoundingBoxDescent,
> >>> emHeightAscent and emHeightDescent.
> >>>
> >>>

> >>> *TAG Review:*

> >>> https://github.com/w3ctag/design-reviews/issues/302
> >>>
> >>> Summary
> >>>
> >>> this is 2nd attempt to ship TextMetrics (first attempt link

> >>> <https://groups.google.com/a/chromium.org/forum/#!searchin/blink-dev/intent$20to$20ship$20textmetrics%7Csort:date/blink-dev/KQW4thKogkk/SiE-xZ7OAQAJ>).

> >>> The current canvas TextMetrics API only exposes the width of the measured
> >>> text. Part of the new API was already implemented under a flag, but there
> >>> were some inconsistencies and bugs, especially with RightToLeft text.
> >>>
> >>> The feature bug (https://crbug.com/277215) has strong user support (24
> >>> stars, 3 more stars since Sept 2018).
> >>>
> >>> Link to “Intent to Implement” blink-dev discussion
> >>>
> >>>
> >>> https://groups.google.com/a/chromium.org/forum/?fromgroups#!searchin/blink-dev/textmetrics|sort:date/blink-dev/SgofW_bQ3ps/jNYamQHplAMJ
> >>>
> >>> The thread was titled “Intend to ship”, but it was seen as “Intend to
> >>> implement” and was never actually shipped.
> >>>
> >>> Is this feature supported on all six Blink platforms (Windows, Mac,
> >>> Linux, Chrome OS, Android, and Android WebView)?
> >>>
> >>> Yes
> >>>
> >>> Demo link
> >>>
> >>> -
> >>>
> >>> Debuggability
> >>>
> >>> No DevTools needed for debug. Users can console print the full
> >>> TextMetrics object in one line.
> >>>
> >>> Risks
> >>>
> >>> Interoperability and Compatibility
> >>>
> >>> Safari already has already shipped these metrics following this spec.
> >>> Firefox started development 4 years ago but never shipped
> >>>
> >>>
> >>> Firefox: In development

> >>> <https://bugzilla.mozilla.org/show_bug.cgi?id=1102584>
> >>>
> >>> Safari: Shipped <https://bugs.webkit.org/show_bug.cgi?id=157629>

> >>>
> >>> We know this is a major feature requested by developers (as well as
> >>> internal Google teams like Google Docs). This API will help developers have
> >>> more control and more accurate text rendering. As of today a different way
> >>> to achieve this is by using rendering text to the DOM and using
> >>> getBoundingClientRect to get some measurements. This process requires a
> >>> relayout of the page.
> >>>
> >>> Activation
> >>>
> >>> Enable the platform experiment ExtendedTextMetrics
> >>>
> >>> Is this feature fully tested by web-platform-tests

> >>> <https://chromium.googlesource.com/chromium/src/+/master/docs/testing/web_platform_tests.md>?

> >>> Link to test suite results from wpt.fyi

> >>> <https://wpt.fyi/results/?label=experimental>.

> >>>
> >>> A set of test for each metric, prefixed by “2d.text.measure”:
> >>>
> >>> https://wpt.fyi/results/2dcontext/drawing-text-to-the-canvas
> >>>
> >>>

> >>> Entry on the feature dashboard <http://www.chromestatus.com/>

> >>>
> >>> https://www.chromestatus.com/feature/5307344997056512
> >>>
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> >>> You received this message because you are subscribed to the Google
> >>> Groups "blink-dev" group.
> >>> To unsubscribe from this group and stop receiving emails from it, send
> >>> an email to blin...@chromium.org.
> >>> To view this discussion on the web visit
> >>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAC3hXJcjN0i2%3Dp3aCfXEOQgS_Btwu%3D6nJZU%2BBfVDHVptEmz_ag%40mail.gmail.com

> >>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAC3hXJcjN0i2%3Dp3aCfXEOQgS_Btwu%3D6nJZU%2BBfVDHVptEmz_ag%40mail.gmail.com?utm_medium=email&utm_source=footer>
> >>> .
> >>>
> >>

--
𝄞 L. David Baron http://dbaron.org/ 𝄂
𝄢 Mozilla https://www.mozilla.org/ 𝄂
Before I built a wall I'd ask to know
What I was walling in or walling out,
And to whom I was like to give offense.
- Robert Frost, Mending Wall (1914)

[Yi Xu]

I think #4070 is agreed on.

For #4073, I think there's a misunderstanding of how the line box works. We may try to clear the language, but I don't think the implementation will change at all. Let me try to explain why:

we are using the line box to describe a baseline, so we can have EmHeightAscent/Descent relative to that baseline. Even if we would change the definition, it's still clear that we want the baseline of the line box itself (which is what I think the spec is describing and what both implementations - Safari and Chrome - did), as any other baseline will be useless (for example, on multiline text, or if there are fallback fonts).

[Chris Harrelson]

Hi, is there a resolution on #4073? I see that there seems to be continuing discussion there.

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[Yi Xu]

There is some confusion on the definition of fontBoundingBoxAscent/Descent and EmHeightAscent/Descent. We will try to launch actualBoundingBoxLeft, actualBoundingBoxRight, actualBoundingBoxAscent, actualBoundingBoxDescent first. 

Thank you,

Yi Xu

[Fernando Serboncini]

If we just launch actualBoundingBox* now, we don't need to resolve #4073, and then can come back to launch the remaining entries once all conversations are resolved.

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[Fernando Serboncini]

Just to restate:

We will be launching only actualBoundingBox*, which is not touched by any of the open spec bugs.

After we finish with this, we will keep addressing the open issues and publish a new I2S, once those issues are resolved.

Thanks.

[Chris Harrelson]

Hi Fernando,

Could you update the chromestatus entry accordingly?

https://www.chromestatus.com/feature/5307344997056512

I also think it would be good idea to ping the TAG review with this update.

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[Yi Xu]

I am updating the intent to ship to match what we want to release now:

Spec

https://html.spec.whatwg.org/multipage/canvas.html#textmetrics

we are launching the following attributes in TextMetrics: actualBoundingBoxLeft, actualBoundingBoxRight, actualBoundingBoxAscent, actualBoundingBoxDescent.

TAG Review:

https://github.com/w3ctag/design-reviews/issues/302

Summary

this is 2nd attempt to ship TextMetrics (first attempt link). The current canvas TextMetrics API only exposes the width of the measured text. Part of the new API was already implemented under a flag, but there were some inconsistencies and bugs, especially with RightToLeft text.

The feature bug (https://crbug.com/277215) has strong user support (25 stars, 4 more stars since Sept 2018).

Link to “Intent to Implement” blink-dev discussion

https://groups.google.com/a/chromium.org/forum/?fromgroups#!searchin/blink-dev/textmetrics|sort:date/blink-dev/SgofW_bQ3ps/jNYamQHplAMJ

The thread was titled “Intend to ship”, but it was seen as “Intend to implement” and was never actually shipped.

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

Yes

Demo link

-

Debuggability

No DevTools needed for debug. Users can console print the full TextMetrics object in one line.

Risks

Interoperability and Compatibility

Safari already has already shipped these metrics following this spec. Firefox started development 4 years ago but never shipped

Firefox: Started implementing a while ago

Safari: Shipped

We know this is a major feature requested by developers (as well as internal Google teams like Google Docs). This API will help developers have more control and more accurate text rendering. As of today a different way to achieve this is by using rendering text to the DOM and using getBoundingClientRect to get some measurements. This process requires a relayout of the page.

Activation

Enable the platform experiment ExtendedTextMetrics

Is this feature fully tested by web-platform-tests? Link to test suite results from wpt.fyi.

A set of test for each metric, prefixed by “2d.text.measure”:

https://wpt.fyi/results/2dcontext/drawing-text-to-the-canvas (canvas)

https://wpt.fyi/results/offscreen-canvas/text (offscreen canvas)

Entry on the feature dashboard

https://www.chromestatus.com/feature/5307344997056512

[Chris Harrelson]

LGTM1

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[Daniel Bratell]

LGTM2

/Daniel

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[Yoav Weiss]

LGTM3

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