Daniel Holbert [:dholbert] Reporter
	Description • 6 years ago

Filing this bug to track the img.decode() API.

Apparently Google Images uses it (or wants to) to swap seamlessly from the low-res to high-res image -- right now, that can trigger a flash (in Firefox at least) due to the high res image not being fully decoded when they swap it in. More info in https://twitter.com/jaffathecake/status/925702096300707842 .

(See also bug 1416328 for the decoding attribute, which addresses similar use-cases more declaratively.)

Spec link:
https://html.spec.whatwg.org/multipage/embedded-content.html#dom-img-decode

Chrome's intent-to-implement a while back (they've shipped it now, perhaps WebKit has as well, not sure):
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/LMV9dBG_1-I

GitHub issue where it was specced:
https://github.com/whatwg/html/issues/2037

	Daniel Holbert [:dholbert] Reporter
	Comment 1 • 6 years ago

Also: there's a good overview of the difference between the use-cases for <img decoding="..."> attribute vs. the img.decode() API in this github comment: https://github.com/whatwg/html/issues/1920#issuecomment-256114499

	Andrew Osmond [:aosmond] (he/him) Assignee
	Comment 2 • 6 years ago

I looked into what needed to be done on another bug around the time I implemented the attribute, but as I recall I just never got around to implementing it.

	Andrew Osmond [:aosmond] (he/him) Assignee
	Comment 3 • 6 years ago

First implementation pass:

try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=2dfbf7f3637aa397f1160dcfe2824153280ce8e1

Looks like it wasn't put behind a secure context in WebKit:

https://github.com/WebKit/webkit/commit/5dd19bfca6d603344914633e21db61b038032ea1#diff-5d3129a3412e339516f06e23f221ed36

Nor in Chrome:

https://chromium.googlesource.com/chromium/src/+/a840c6a20c62e5ad20ec4e3419370173566b2850%5E%21/
https://chromium.googlesource.com/chromium/src/+/32a4a668e4e287c99a3917f1fc16e58a66215ef2%5E%21/

	Andrew Osmond [:aosmond] (he/him) Assignee
	Comment 4 • 6 years ago

Still one test failing (locally) but most of the way there now:

try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=1ceedbd18674054ceee009fc296db9a3043aa64a

	Andrew Osmond [:aosmond] (he/him) Assignee
	Comment 5 • 6 years ago

(In reply to Andrew Osmond [:aosmond] from comment #4)
> Still one test failing (locally) but most of the way there now:
> 
> try:
> https://treeherder.mozilla.org/#/
> jobs?repo=try&revision=1ceedbd18674054ceee009fc296db9a3043aa64a

The last failure is weird. The promise is indeed rejected, but it doesn't bubble up to the test framework.

	Andrew Osmond [:aosmond] (he/him) Assignee
	Comment 6 • 6 years ago

(In reply to Andrew Osmond [:aosmond] from comment #5)
> (In reply to Andrew Osmond [:aosmond] from comment #4)
> > Still one test failing (locally) but most of the way there now:
> > 
> > try:
> > https://treeherder.mozilla.org/#/
> > jobs?repo=try&revision=1ceedbd18674054ceee009fc296db9a3043aa64a
> 
> The last failure is weird. The promise is indeed rejected, but it doesn't
> bubble up to the test framework.

Spoke with arai on IRC about this, it looks like we kill the global object when the iframe is removed, so the promises are dropped on the floor, despite me issuing the rejection. I'll leave the test case failing for now.

	Andrew Osmond [:aosmond] (he/him) Assignee
	Comment 7 • 6 years ago

try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=e7b4ae32b697cf8dd9ff5759cd03d7e8d7be6bb7

	Andrew Osmond [:aosmond] (he/him) Assignee
	Comment 8 • 6 years ago

The img decode API allows a web author to request that an image be
decoded at its intrinsic size and be notified when it has been
completed. This is useful to ensure an image is ready to display before
adding it to the DOM tree -- this will help reduce flickering.

	Andrew Osmond [:aosmond] (he/him) Assignee
	Comment 9 • 6 years ago

try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=031dbae59ef3d891e85f19904223aaebfeb43fa8

	Pulsebot
	Comment 16 • 5 years ago

Pushed by aosmond@gmail.com:
https://hg.mozilla.org/integration/mozilla-inbound/rev/5a7f8303d682
Implement img decode API. r=bzbarsky,tnikkel