January 2020 - webkit-dev - lists.webkit.org

Request for feedback on CompressionStream and DecompressionStream
by Adam Rice 02 May '22

02 May '22

I am trying to gauge feedback on compression streams with a view to shipping them in Chromium. Very briefly, they are a way to do gzip and gunzip in the browser. Less briefly, the explainer https://github.com/WICG/compression/blob/master/explainer.md goes into some detail of the how and why. The specification https://wicg.github.io/compression/ gives verbose detail of how. You may also find the W3C TAG review https://github.com/w3ctag/design-reviews/issues/410 interesting. Any and all feedback is welcome! FAQ: Q. Will this support brotli, zstd, etc.? A. Not yet. It's on the radar. Thanks, Adam Rice, Chromium

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Implementing MathML stylistic attributes in WebKit
by Frédéric Wang 28 Sep '20

28 Sep '20

Hello, Currently MathML attributes mathvariant, displaystyle and scriptlevel [1] [2] are implemented in WebKit using custom "style resolution" and "one-glyph rendering" inside the MathML layout code [3] [4] [5]. These features involve text rendering and interaction with CSS font-size, so it is difficult to implement them properly and completely that way. There are known bugs and missing features right now (e.g. mathvariant transform only applies to one-character strings, automatic displaystyle/scriptlevel does not work with fractions, etc) Several years ago, Gecko used to do something similar but that was causing a lot of problems (dynamic update, assertion failures...). At the end, this is now implemented in Gecko more reliably by mapping the attributes to internal CSS properties ; [6] is based on that. When I tried to do something like this in WebKit three years ago, I was only able to rely on proprietary -webkit-* extensions exposed to users [7]. So my questions are: (1) What is WebKit's mechanism to implement such stylistic attributes? (2) Is it possible to implement internal (i.e. not web-exposed to users) CSS properties/values in WebKit? (3) Is it ok to add more -webkit-* properties/values or should these properties be standardized at the CSS WG instead? I understand answers to these general questions from other browser project is either use internal properties or standardize them. Thanks, Frédéric PS: For a concrete example, see [8]. Automatic mathvariant is used for italic variables while font-size in fractions is calculated according to displaystyle / scriptlevel rules. The latter is incorrect (check the attached screenshot) while selection highlight is broken for the former. [1] https://mathml-refresh.github.io/mathml-core/#the-mathvariant-attribute [2] https://mathml-refresh.github.io/mathml-core/#the-displaystyle-and-scriptle… [3] https://trac.webkit.org/browser/webkit/trunk/Source/WebCore/css/mathml.css [4] https://trac.webkit.org/browser/webkit/trunk/Source/WebCore/rendering/mathm… [5] https://trac.webkit.org/browser/webkit/trunk/Source/WebCore/rendering/mathm… [6] https://mathml-refresh.github.io/mathml-core/#css-extensions-for-math-layout [7] https://bugs.webkit.org/show_bug.cgi?id=133845#c5 [8] https://bug-201242-attachments.webkit.org/attachment.cgi?id=377730 -- Frédéric Wang

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PSA: Bit fields won't be packed on Windows if you mix types
by Ryosuke Niwa 04 Sep '20

04 Sep '20

Hi, Unlike gcc and clang, MSVC pads each consecutive member variables of the same type in bitfields. e.g. if you have: struct AB { unsigned m_1 : 31; bool m_2 : 1; } then *MSVC pads m_1 and allocates sizeof(unsigned) * 2 for AB* whereas gcc and clang only allocate sizeof(unsigned) * 1 for AB. This is *not a compiler bug*. It's a spec. compliant behavior, and may in fact have a better run-time performance in some situations. However, for core objects like RenderObject and InlineBox, allocating extra 4-8 bytes per each object is prohibitory expensive. In such cases, please *use the same POD type for all bitfield member variables*. (Storage class classifiers and variable qualifiers seem to have no effect on how variables are packed; e.g. mutable, const, etc...). For example, MSVC will allocate sizeof(unsigned) * 1 for AB if we rewrite the above code as: struct AB { unsigned m_1 : 31; unsigned m_2 : 1; } When you're making this change, *be sure to audit all code that assigns a non-boolean value to m_2* because implicit type coercion into boolean is no longer in effect. For example, AB ab; ab.m_2 = 2; puts(ab.m_2 ? "true" : "false"); will print "true" before the change and will print "false" after the change. An easy way to ensure you've audited all such code is to add getters and setters for all bitfield member variables or wrap them in a special structure or class as done in http://trac.webkit.org/changeset/103353 and http://trac.webkit.org/changeset/104254. Best regards, Ryosuke Niwa Software Engineer Google Inc.

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Feedback on Blink's text fragment directive proposal
by David Bokan 31 Aug '20

31 Aug '20

Hello webkit-dev, I'd like to solicit feedback as well as an official position from Webkit on our proposal for the text fragment directive: https://github.com/WICG/ScrollToTextFragment. In summary: this is a feature that allows authors and users to craft URLs to pages and specify a snippet of text on the page as a subresource (visually highlighting it and scrolling it into view). Analogous to element-id based fragment anchors but for text. You can try this out today in Chrome Beta by enabling chrome://flags/#enable-text-fragment-anchor. Here's an example link: https://en.wikipedia.org/wiki/Uniform_Resource_Identifier#:~:text=An%20opti… Relevant Links: <https://github.com/WICG/ScrollToTextFragment/blob/master/README.md> Explainer <https://github.com/WICG/ScrollToTextFragment/blob/master/README.md> Spec <https://wicg.github.io/ScrollToTextFragment/> TAG Review <https://github.com/w3ctag/design-reviews/issues/392> (Currently Suspended) Blink Intent Thread <https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/zlLSxQ9BA8Y/…> Issue on Mozilla standards-positions <https://github.com/mozilla/standards-positions/issues/194> We've been using the GitHub repo for issue tracking but happy to take feedback (official or otherwise) in any form. Thank you! David

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EWS now parses error logs in case of build failure
by Aakash Jain 11 Aug '20

11 Aug '20

Hi Everyone, I am happy to announce another EWS feature. From now on, in case of build failure, EWS will parse the errors and display them in a separate 'errors' log. You wouldn't have to search through thousands of lines of logs to find the error message. For example, in https://ews-build.webkit.org/#/builders/16/builds/6054, in step #7 WebKit failed to compile. Complete logs (stdio) are 38,000+ lines, and the error is not at the end of the logs. Normally, it requires some searching through the logs to find the relevant errors. But now, there is another 'errors' log, which contains just the relevant 11 lines (containing error and few related lines to provide additional context). Hopefully this would save some time and efforts previously spent on searching through the large logs. Note that this information is not displayed in status-bubble tool-tip, since this might be lot of text to display in the tooltip. My further plan is to make this information more readily available, by adding it to a custom designed page which will open on clicking the status bubble https://webkit.org/b/197522 Please let me know if you notice any issues or have any feedback. Thanks Aakash Reference: https://webkit.org/b/203418

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Support "registerProtocolHandler" in WebKit2
by Gyuyoung Kim 20 Apr '20

20 Apr '20

Hello, I would like to listen what do you think to support 'registerProtocolHandler' in WebKit2. This feature is to execute web content through registered custom protocol. - For example, web content can register "mailto" custom protocol using this feature, <script> navigator.registerProtocolHandler("mailto", "https://mail.naver.com/", "Web Mail"); </script> <html> <head> <title>Web Protocol Handler Sample - Test</title> </head> <body> <p>Send an email : <a href="mailto://">this !</a></p> </body> </html> Besides this feature has been supported by Mozilla and Chromium (From Mozilla 3.0, Chromium 13). - https://developer.mozilla.org/en-US/docs/Web/API/Navigator/registerProtocol… - https://developer.mozilla.org/en/docs/Web-based_protocol_handlers The feature is included in the W3C recommendation 28 released on Oct. 2014. - W3C spec : http://www.w3.org/TR/html5/webappapis.html#custom-handlers IIRC, some WebKit1 ports supported this feature though, those ports were deprecated. Now WebKit port supports this feature no more. There is a very old bug to support this feature though, it wasn't maintained so far. Recently I updated it based on latest WebKit. - https://bugs.webkit.org/show_bug.cgi?id=92749 Feel free to give me any feedback about this feature. Gyuyoung.

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Changing the svn commit hook to allow tabs for tests.
by Keith Miller 04 Apr '20

04 Apr '20

Hi all, I don’t know if this is possible but it would be great if some sub-directories could be excluded from the no-tabs pre-commit hook. For example, there are many test262 tests that contain tabs, either because they intentionally try to test parsing tab characters or because they were written by someone that used them. Regardless, it’s pretty inconvenient to add the svn attribute that allows tabs every time I update the tests. Since svn properties can’t apply to directories, as far as I know, there’s no way to add the “allow-tabs” property to the entire test262 directory. Alternatively, we could remove the pre-commit hook as tabs should be caught by the style-checker anyway. This is a more contentious choice so I’m not proposing it as the first option unless someone else wants to push for it. Cheers, Keith Miller

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Content-DPR: Image resolution optimization at CDN/transport layer
by Noam Rosenthal 11 Mar '20

11 Mar '20

Hola I would like to open a discussion that has started a few years back and has never reached a consensus: https://bugs.webkit.org/show_bug.cgi?id=145380 In a nutshell: content-dpr is a response-only header for images, that allows servers at transient layers (CDNs/proxies) to optimize images by changing their resolution, allowing the user agents to compensate for the change in intrinsic size caused by the resolution change - thus making the resolution change transparent to users. It's the header that makes the resolution-encoding transparent. The feature is already up and running in chrome since version 67, and is used by some CDNs. Since there was lack of consensus in the bug discussion, I wanted to make the case for it here, and see if opinions about the subject can be voiced before we reach a decision/consensus. I tried to find a good balance between being detailed and being concise. — Players in CDN, proxy and other transient parts of the internet world have innovated a lot in the past few years. There are lots of interesting companies and competition there. One of the areas of this innovation is in optimizing images in a transparent way at transient layers (proxy/CDN). This makes a lot of sense considering how much of internet traffic is taken by image download. What the research at the CDN companies found, was that modifying resolution at the transient layer can have a tremendous effect on performance/user-experience balance, for example by serving lower-resolution versions of the images when network traffic is costly/slow (the exact formula for that is part of where the CDN can innovate). More details on that innovation in the links below. The thing is, that modifying image resolution at the CDN/proxy is not inherently transparent, due to one reason - layout is affected by the image’s intrinsic size, and changing the image’s resolution inadvertently changes the image’s intrinsic size. To make this transparent, the user agent has to be involved, to compensate for this optimization when reading the image’s intrinsic size. The main case against this feature was that image resolution is a feature that should be handled at the markup layer and not at the transport layer ( https://bugs.webkit.org/show_bug.cgi?id=145380#c7) I would argue that http-headers are not a transport layer (TCP/UDP etc.), but rather part of an application-layer protocol that is designed, in part, to pass information to the transient layers such as CDNs, and that resolution compression is a (new, image-specific) equivalent of transfer-encoding. Also, as a response to the view that this should be part of markup, I would argue that those transparent decisions by the servers should not concern web authors at all. It’s an optimization decision to be handled by the servers, with the user agent doing nothing about it but allow that decision to be transparent in terms of layout (the same way gzip and cache-control are transparent). What is offered here is a win-win in terms of delivering images, and would allow webkit-browser users to enjoy some of the innovations in the image delivery world without modifying their HTML content and without concern of breaking their layouts. Less battery and data used for downloading big images at certain situations, for example. I hope this provides enough background without being too tedious. I would be happy to shed more light on whatever is missing in this longish essay :) Additional info: https://github.com/eeeps/content-dpr-explainer https://cloudinary.com/blog/client_hints_and_responsive_images_what_changed… https://www.chromestatus.com/metrics/feature/timeline/popularity/906

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Position on emerging standard: video.requestAnimationFrame()
by Thomas Guilbert 29 Feb '20

29 Feb '20

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. Thank you! Thomas

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Is anyone maintaining Nicosia scrolling code?
by Simon Fraser 27 Feb '20

27 Feb '20

There’s a bunch of code in Source/WebCore/page/scrolling/nicosia/ that I keep breaking with scrolling tree refactoring. Most of it it stubs. Is anyone maintaining this code, because it obviously doesn’t work, and I’d like to remove the maintenance burden. Simon

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