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Modernize algorithms in "Algorithm" section (#120)
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The original main goal was to give a name to the existing algorithm that
used to run in the "next animation frame task" so that it could be
referenced in the upcoming WebDriver section, but "animation frame task" as
a concept did not exist, and one thing led to another and the final change
includes a better version of the original algorithms, but without any
user-visible changes.

This change borrows a lot of ideas from the Screen Orientation spec as of
its 2023-08-09 Editor's Draft.

Most important changes:
- The "update the device posture information" algorithm was renamed to
  "calculate the device posture information" so that it returns a value
  instead of updating `[[CurrentPosture]]` directly -- that is done as task
  queued in the user interaction task source (more on this below).
- Call the main algorithm "device posture change steps".
- Merge the separate page visibility-related algorithm into the main one,
  and add the proper checks to it to ensure that documents whose visibility
  state is "hidden" are not updated and that calls to "update the device
  posture information" that result in the same value being stored do not
  fire any "change" events.
- The "change" event is now queued to be fired in the user interaction task
  source so that the moment it is actually fired is more predictable (the
  "device posture change steps" are not running at any specific point of the
  HTML event loop).

While here: the definition of the `onchange` attribute was updated to
mention the current terms defined in the HTML spec, along with a proper
`<dfn>` for the event handler event type.

The language and the references used in the text have also been updated: we
no longer deal with browsing contexts, but with navigables; the
PAGE-VISIBILITY spec is no longer treated as a separate specification, as it
was merged into HTML a few years ago.

Related to #104. Fixes #95.
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@rakuco
rakuco committed Mar 8, 2024
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Showing 1 changed file with 61 additions and 83 deletions.
144 changes: 61 additions & 83 deletions index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -250,9 +250,10 @@ <h3>
The <dfn>onchange</dfn> attribute: Handle posture changes
</h3>
<p data-link-for="DevicePosture">
The {{onchange}} attribute is an <a data-cite="html">event
handler</a> whose corresponding <a data-cite="html">event handler
event type</a> is "<code>change</code>".
The {{onchange}} attribute is an <a>event handler IDL attribute</a>
for the {{onchange}} [=event handler=], whose [=event handler event
type=] is "<dfn class="event" data-dfn-for=
"DevicePosture">change</dfn>".
</p>
</section>
</section>
Expand Down Expand Up @@ -378,8 +379,8 @@ <h2>
{{Document/[[CurrentPosture]]}}, which should be initialized when the
<a>document</a> is created, otherwise they MUST be initialized the
first time they are accessed and before their value is read. The
<a>user agent</a> MUST <a>update the device posture information</a> of
the <a>document</a> to initialize it.
<a>user agent</a> MUST run the <a>device posture change steps</a> with
the <a>document</a> and true to initialize it.
</p>
<p>
For a given <a>document</a>, the <a>current posture</a> is derived from
Expand Down Expand Up @@ -445,17 +446,18 @@ <h3>
</h3>
<section data-link-for="DevicePosture">
<h2>
Updating the device posture information
Calculating the device posture information
</h2>
<p>
The steps to <dfn>update the device posture information</dfn> of a
<a>document</a> are as follows:
The steps to <dfn>calculate the device posture information</dfn> of a
{{Document}} |document:Document| are as follows:
</p>
<ol class="algorithm">
<li>Update the <a>document</a>.{{Document/[[CurrentPosture]]}} given
current hinge angle value, <a>current screen orientation</a>, as well
as potential implementation-specific signals, according to <a>posture
values table</a>.
<li>Return a {{DevicePostureType}} value determined in an
[=implementation-defined=] way based on the current hinge angle
value, [=current screen orientation=], as well as potential
implementation-specific signals, according to the [=posture values
table=].
</li>
</ol>
</section>
Expand All @@ -464,74 +466,70 @@ <h2>
Device Posture change
</h2>
<p>
Whenever the screen(s) fold angle, screen orientation or device
specific signals change, the <a>user agent</a> MUST run the following
steps as part of the next <a>animation frame task</a>:
When the user agent determines that the screen(s)' fold angle,
orientation or device-specific signals have changed for a [=top-level
traversable=], it MUST run the [=device posture change steps=] with
the [=top-level traversable=]'s [=navigable/active document=].
</p>
<p>
The <dfn>device posture change steps</dfn> for a {{Document}}
|document:Document| and an optional boolean |disallowRecursion|
(default false) are as follows:
</p>
<ol class="algorithm">
<li>Let |browsing contexts| be the <a>list of the descendant browsing
contexts</a> of the <a>top-level browsing context</a>'s
<a>document</a>.
<li>If |document|'s [=Document/visibility state=] is "hidden", then
abort these steps.
</li>
<li>Let |posture| be the result of invoking [=calculate the device
posture information=] with |document|.
</li>
<li>[=list/for each=] |context:browsing context| in |browsing
contexts|, run the following sub-steps:
<li>If |posture| is equal to
|document|.{{Document/[[CurrentPosture]]}}, abort these steps.
</li>
<li>[=Queue a global task=] on the [=user interaction task source=]
with |document|'s [=relevant global object=] to perform the following
steps:
<ol>
<li>Let |document| be the |context|'s [=navigable/active
document=].
</li>
<li>If |document| is not visible per [[PAGE-VISIBILITY]], abort
these steps.
<!-- We should use [=associated `Navigator`=], but the <dfn> is not exported by the
HTML spec. -->
<li>Set |documet|.{{Document/[[CurrentPosture]]}} to |posture|.
</li>
<li>
<a>Update the device posture information</a> of |document|.
<li>[=Fire an event=] named "{{DevicePosture/change}}" at the
{{DevicePosture}} object associated with |document|'s [=relevant
global object=]'s associated {{Navigator}}.
</li>
<li>
<a>Fire an event</a> named `change` at |document|'s
{{Window.navigator.devicePosture}} object.
</ol>
</li>
<li>If |disallowRecursion| is true, abort these steps.
</li>
<li>[=List/For each=] |descendantNavigable| of |document|'s
[=Document/descendant navigables=]:
<ol>
<!-- If we do not pass true below, each descendant document will recurse into its
descendants too. -->
<li>Run the [=device posture change steps=] with
|descendantNavigable|'s [=navigable/active document=] and true.
</li>
</ol>
</li>
</ol>
<p>
Whenever a <a>document</a> becomes visible per [[PAGE-VISIBILITY]],
in other words after the <a>now visible algorithm</a> is run, the
<a>user agent</a> MUST run the following substeps as part of the next
<a>animation frame task</a>:
This specification defines the following [=page visibility change
steps=] given |visibility state| and |document:Document|:
</p>
<ol class="algorithm">
<li>Let |document| be the <a>document</a> in question.
</li>
<li>Let |posture| be the |document|.{{Document/[[CurrentPosture]]}}.
</li>
<li>
<a>Update the device posture information</a> of the |document|.
</li>
<li>If |posture| is different from the
|document|.{{Document/[[CurrentPosture]]}}, run the following
sub-steps:
<ol>
<li>
<a>Fire an event</a> named `change` at the |document|'s
{{Window.navigator.devicePosture}} object.
</li>
</ol>
<li>Run the [=device posture change steps=] on |document|.
</li>
</ol>
<div class="note">
<aside class="note">
<p>
Developers need to be aware that a
{{Window.navigator.devicePosture}} object from a <a>document</a>
that is not visible, as per [[PAGE-VISIBILITY]], will not receive
an orientation change event. This is to prevent unnecessary changes
to layout, etc. in the non-visible web application.
Developers need to be aware that [=documents=] with a "hidden"
[=Document/visibility state=] will not receive a device posture
change event. However, once the [=document=] becomes visible again,
it will receive the change event.
</p>
</div>
<div class='issue'>
This section could be improved if the [[PAGE-VISIBILITY]]
specification had a hook for when the document becomes visible and
hidden. <a href='https://github.com/w3c/page-visibility/pull/54'>PR
54</a>.
</div>
</aside>
<div class="issue" data-number="103"></div>
</section>
</section>
<section>
Expand Down Expand Up @@ -697,26 +695,6 @@ <h2>
"MEDIAQ#mq-boolean-context">Evaluating Media Features in a Boolean
Context</dfn>.
</p>
<p>
The following concepts and interfaces are defined in [[HTML]]:
<dfn data-cite=
"HTML/browsers.html#list-of-the-descendant-browsing-contexts">list of
the descendant browsing contexts</dfn>.
</p>
<p>
The following is defined in [[PAGE-VISIBILITY]]: <dfn data-cite=
"PAGE-VISIBILITY#dfn-now-visible-algorithm">now visible
algorithm</dfn>.
</p>
<p>
The following is used but not defined in [[FULLSCREEN]]: <dfn><a href=
'https://github.com/whatwg/fullscreen/issues/16'>animation frame
task</a></dfn>.
</p>
<div class='issue'>
This should now be updated since the <a>animation frame task</a> issue
is recently resolved and the timing is now defined.
</div>
</section>
<section id="conformance">
<p>
Expand Down

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