[webkit-dev] Position on emerging standard: video.requestAnimationFrame()

[Ken Russell]

It seems to have similar behavior to me: on a window or worker, the
requestAnimationFrame callback needs to re-schedule itself before exiting,
in order to be called again in the future. The proposed
HTMLVideoElement.requestAnimationFrame works similarly. A single
onFrameAvailable callback defined on the HTMLVideoElement would behave
fairly differently. Domenic Denicola's feedback on using
requestAnimationFrame vs. a promise
<https://github.com/w3ctag/design-reviews/issues/429#issuecomment-558850179>
resonates
with me.

-Ken


On Mon, Feb 3, 2020 at 11:52 AM Simon Fraser <simon.fraser at apple.com> wrote:

>
>
> On Feb 3, 2020, at 11:25 AM, Ken Russell <kbr at google.com> wrote:
>
> The name "requestAnimationFrame" was chosen mainly to achieve parity with
> the AnimationFrameProvider mixin, which now provides the same animation
> facility to the main thread and dedicated workers:
>
> https://html.spec.whatwg.org/multipage/imagebitmap-and-animations.html#animation-frames
> https://discourse.wicg.io/t/proposal-video-requestanimationframe/3691
>
> It offers a nice symmetry with other JavaScript-driven animations.
>
>
> But the video.requestAnimationFrame behavior seems fundamentally different
> to window.requestAnimationFrame. It feels like it's conflating two
> different things.
>
> Simon
>
>
> -Ken
>
>
>
> On Mon, Feb 3, 2020 at 6:58 AM Philip Jägenstedt <foolip at chromium.org>
> wrote:
>
>> Hi Simon,
>>
>> Naming is hard as usual and was discussed on
>> https://github.com/w3ctag/design-reviews/issues/429, where you've
>> already commented.
>>
>> Is there a pair of names that you think would work better
>> here? onFrameAvailable() would IMHO be quite unidiomatic, the web platform
>> doesn't have any other onFoo() methods, and what would the "cancel" variant
>> be called?
>>
>> Can you file an issue in https://github.com/WICG/video-raf/issues if you
>> see a good alternative?
>>
>> Also curious if +Eric Carlson <eric.carlson at apple.com> has any feedback
>> on this?
>>
>> On Wed, Jan 22, 2020 at 10:49 PM Simon Fraser <simon.fraser at apple.com>
>> wrote:
>>
>>>
>>> On Jan 21, 2020, at 5:27 PM, Thomas Guilbert <tguilbert at google.com>
>>> wrote:
>>>
>>> The idea was to reuse an API name that developers are already
>>> familiar with, in a similar context. The name is also being used in
>>> XRSession (
>>> https://developer.mozilla.org/en-US/docs/Web/API/XRSession/requestAnimationFrame),
>>> and in OffscreenCanvas (or technically DedicatedWorkerGlobalScope). The AnimationFrameProvider
>>> mixin
>>> <https://html.spec.whatwg.org/multipage/imagebitmap-and-animations.html#animationframeprovider> could
>>> also be updated so HTMLVideoElement can extend it.
>>>
>>> Yes, this isn't formally spec'ed out, but it will be. For now, they are
>>> added to the task queue and run like any other task. So, going off the spec
>>> you linked, I think this would be "5) Perform oldestTask's step"  and not
>>> "10) Rendering: [...] 11. Foreach document run animation frame callbacks
>>> for that Document".
>>>
>>>
>>> I would expect something that's called "requestAnimationFrame" to only
>>> fire in the "update the rendering" steps; requestAnimationFrame is a
>>> "before rendering" callback. So firing a callback with the same name at
>>> other times seems like it will lead to author confusion.
>>>
>>> The author's expectation should be that any content/style changes they
>>> make inside a requestAnimationFrame callback will appear on-screen in the
>>> same frame as other changes in the same event loop cycle, and that
>>> requestAnimationFrame won't be called more often than is necessary to
>>> update the screen at the appropriate frame rate.
>>>
>>> Simon
>>>
>>>
>>> On Tue, Jan 21, 2020 at 1:01 PM Simon Fraser <simon.fraser at apple.com>
>>> wrote:
>>>
>>>> On Jan 21, 2020, at 12:37 PM, Thomas Guilbert <tguilbert at google.com>
>>>> wrote:
>>>>
>>>> Hello,
>>>>
>>>> I'm reaching out to see if webkit would like to weigh in on the following proposal:https://discourse.wicg.io/t/proposal-video-requestanimationframe/3691
>>>>
>>>> The HTMLVideoElement.requestAnimationFrame() API allows web developers to be notified when a video frame has been presented for composition, and provides metadata for that frame.
>>>>
>>>> If you want to try it out, a prototype is available in Chromium Dev,
>>>> behind the enable-experimental-web-platform-features flag.
>>>>
>>>>
>>>> This is not official feedback, but I have some issues with the proposal.
>>>>
>>>> First, the name is confusing. It sounds like you're requesting a frame
>>>> from the video, but it's really a "frame available" callback. Why not call
>>>> it onFrameAvailable()?
>>>>
>>>> Second, its interaction with normal requestAnimationFrame() and the
>>>> HTML event loop needs to be better defined. Where in in the
>>>> https://html.spec.whatwg.org/multipage/webappapis.html#event-loop-processing-model do
>>>> these callbacks fire?
>>>>
>>>> Simon
>>>>
>>>>
>>>>
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