On Fri, Oct 30, 2020 at 1:58 PM Nicolás Peña Moreno <n...@google.com> wrote: > > Hi, I'd like to request WebKit's position on the Element Timing API, which lets web developers annotate images or text whose performance they care about. They can then obtain rendering timestamps from the PerformanceObserver. For cross-origin images the detailed information is gated on Timing-Allow-Origin. The proposed specification is at https://wicg.github.io/element-timing/ and is currently shipped in Chromium. Thanks!
Apple's WebKit team reviewed this API and we have a few concerns including but not limited to: - The proposed API exposes timing at which a given element is painted. Implemented naively, this exposes the implementation detail of what kind of compositing tiles are used on a given web page. Hiding this implementation detail and recording the exact theoretical paint timing will be prohibitively expensive to do on all websites. - The definition of the set of owned text nodes and how they compute intersectionRect seems inadequate. It's unclear what "border box" of *Text* node would mean. The spec doesn't seem to ever populate "set of elements with rendered text" either. - The use of this API seems to incur a significant runtime as well as memory cost. - R. Niwa
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