On Mon, Mar 2, 2020 at 2:37 AM Maciej Stachowiak <m...@apple.com> wrote:
> > > On Mar 1, 2020, at 4:19 PM, Noam Rosenthal <n...@webkit.org> wrote: > OK, to summarize what I got from this > - we want the spec and webkit painting to be as close as possible > - The spec needs to be clearer/less buggy about a few things, such as > "White" canvas, spec issues to be files > - WebKit should be closer to the spec wrt canvas, backgrounds and > potentially pixel/character threshold (TBD) > - FP is more sensitive than FCP, because it exposes browser differences > and may lead to unwanted comparisons and misunderstanding. Thus, it should > be exposed as a different runtime feature flag. > > One thing I'm wondering about - would it be better to change the rendering > heuristics together with implementing the paint API reporting? Or would it > be better to separate those concerns a bit in terms of implementation? I > mean, having the performance APIs in the code behind 2 flags with failed > tests conforming to the spec might help iterate on the actual rendering. > What would you consider a better approach here? > > > If I were doing this myself, I’d first change rendering heuristics > (probably without a flag) and then add the web-facing API. > Okay, let's see how that goes. > What you describe might be reasonable if there are WPT conformance tests > that can distinguish cases where the FCP timing is too late or too soon. > It’s probably possible to make such tests, but I am not sure if they > already exist. > They exist to some extent, webkit currently fails 4 out of 13 painting-API conformance tests, around some of the issues discussed here (e.g. one of the tests fails because webkit doesn't consider background image to be contentful). I think I'll work on a few more while working on the spec, they're quite easy to write. Cheers Noam
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