LGTM2
On 9/21/22 7:44 AM, Yoav Weiss wrote:
LGTM1
It seems unlikely that even the (few) developers who access this data
are somehow relying on it.
On Tue, Sep 20, 2022 at 8:10 PM Dale Curtis <[email protected]>
wrote:
On Tue, Sep 20, 2022 at 3:36 AM Yoav Weiss
<[email protected]> wrote:
On Fri, Sep 16, 2022 at 11:19 PM Dale Curtis
<[email protected]> wrote:
Contact emails
[email protected]
Explainer
None
Specification
https://github.com/w3c/webcodecs/issues/508
Summary
premultiplyAlpha tells ImageDecoder to multiply the alpha
channel into the RGB channels of decoded images. It was
added to mirror the capabilities of ImageBitmapOptions,
but in retrospect doesn't make sense.
Feature has no observable effects in primary use
cases (drawing), but may constrain implementations
in suboptimal ways. E.g., requiring YUV be
converted to RGB. See
https://github.com/w3c/webcodecs/issues/508 for a
more detailed description. Per consensus of
WebCodecs spec editors and lack of usage
(0.000000339% - 0.00000687% of page loads per a
UseCounter in M105), we propose deprecating and
removing this feature starting with M108.
What would breakage look like? What would happen to callers
who still pass that option?
If they're just drawing the frames into canvas, webgl, etc there
is no observable difference or breakage (this is the common use
case) - since the draw stage takes care of any alpha blending. If
they're accessing the raw pixels via VideoFrame::copyTo() they
would notice that the alpha is no longer premultiplied. Depending
on what the application is doing with the frames this may mean
nothing (i.e., not using images w/ alpha, or didn't care about
alpha) or it could result in color changes in the image.
Blink component
Blink>Media>WebCodecs
<https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3EMedia%3EWebCodecs>
TAG review
Not applicable
TAG review status
Not applicable
Risks
It's possible that there exists some client which was
accessing raw pixel data in JavaScript may observe that
the alpha channel is no longer premultiplied into RGB
channels. Clients wishing for this functionality can
either do the multiply themselves or use
createImageBitmap() to do this.
Interoperability and Compatibility
/Gecko/: Positive Firefox co-editor supports removal.
I don't know if we can consider this
<https://github.com/w3c/webcodecs/issues/508#issuecomment-1248720618>
a Mozilla position. At the same time, this seems small enough
to not warrant an explicit issue. (and it's good to have
consensus on the issue)
That's a bit surprising. I think that's a pretty strong signal,
but defer to the API owners.
That's a strong signal from the person editing the spec, but not an
official Mozilla position.
/WebKit/: No signal
/Web developers/: No signals
/Other signals/: Microsoft co-editor supports removal.
WebView application risks
Does this intent deprecate or change behavior of
existing APIs, such that it has potentially high
risk for Android WebView-based applications?
No.
Debuggability
n/a
Will this feature be supported on all six Blink
platforms (Windows, Mac, Linux, Chrome OS,
Android, and Android WebView)?
Yes
Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?
Yes
Flag name
n/a
Requires code in //chrome?
False
Tracking bug
https://bugs.chromium.org/p/chromium/issues/detail?id=1340190
Launch bug
https://bugs.chromium.org/p/chromium/issues/detail?id=1340190
Estimated milestones
M108
Anticipated spec changes
Open questions about a feature may be a source of
future web compat or interop issues. Please list
open issues (e.g. links to known github issues in
the project for the feature specification) whose
resolution may introduce web compat/interop risk
(e.g., changing to naming or structure of the API
in a non-backward-compatible way).
https://github.com/w3c/webcodecs/pull/562
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/4560781148946432
This intent message was generated by Chrome
Platform Status <https://chromestatus.com/>.
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