Just a heads up about WebKit changing behavior on a couple of things. Bugs here refers to https://bugs.webkit.org/show_bug.cgi?id=<bug_number>
* Bug 149968 - Web pages with unscalable viewports shouldn't have a single tap delay * Bug 150604 - Implement viewport-width-based fast-click heuristic * Bug 149854 - Implement touch-action: manipulation; for iOS The article on WebKit blog https://webkit.org/blog/5610/more-responsive-tapping-on-ios/ Excerpt: > WebKit on iOS has a 350 millisecond delay before single taps activate links > or buttons. WebKit has this delay because we also allow users to double tap > to zoom, which is a great way to zoom in on content that is well-sized for > large desktop displays, but appears too small on mobile devices. However, > when a user has tapped once, WebKit cannot tell if the user intends on > tapping again to trigger a double tap gesture. Since double tapping is > defined as two taps within a short time interval (350ms), WebKit must wait > for this time interval to pass before we’re sure that the user intended to > tap only once. > > We know that responsive tapping is really important to web developers — so > much so that many are willing to employ JavaScript frameworks to avoid the > delay using touch handlers. Instead of waiting for WebKit to fire a click > after a delay, these libraries prevent the default behavior of the touchend > event and call `click()` immediately so that the element is clicked the > moment the user stops touching the element. While this may make a link feel > fast, it can also reduce responsiveness in other ways, including page load > time and scrolling. To address this, we baked fast tapping optimizations into > WebKit so well-scaled mobile web pages will be able to achieve responsive > tapping out of the box without the drawbacks of third-party frameworks. > > On web pages optimized for mobile viewports, elements such as links and form > controls are scaled to fit well on smaller screens. As such, double tapping > on these elements increases the page scale by only a small amount. Since > double tapping provides little value on these web pages, we’ve implemented a > mechanism for removing the delay for single taps by disabling double tap > gestures. > > The following examples show the amount of time required to tap a button 10 > times in a page with `<meta name="viewport" content="initial-scale=1.0, > width=device-width">`, with and without the fast-tap optimization. The left > video shows the old behavior, while the right video shows the new behavior. > > ### When Fast-Tap Optimizations Apply > > When content is scaled to fit well on a mobile device, WebKit disables double > tapping in favor of fast single tapping. Using the viewport meta tag, there > are a few ways WebKit determines whether content is well-proportioned, for > both scalable and unscalable web pages. > > Since users cannot zoom in unscalable viewports (using meta tags with > `user-scalable=no` or a `minimum-scale` equal to the `maximum-scale`) WebKit > assumes that if a page has an unscalable viewport, all content is already > well-proportioned relative to the screen. On these pages, WebKit removes the > ability to double-tap on elements altogether and dispatches all taps > immediately as clicks. We implemented this behavior in [Bug > #149968](https://bugs.webkit.org/show_bug.cgi?id=149968). > > However, we believe web pages should be scalable when possible. For this > reason, viewports that have `width=device-width` will have fast single > tapping when the user is at initial scale. We added this optimization in [Bug > #150604](https://bugs.webkit.org/show_bug.cgi?id=150604). > > ### Styling Fast-Tap Behavior > > Even if a web page cannot use one of the viewport configurations above, it > can still opt in to the fast-tap optimization. We’ve implemented the > `manipulation` value of the new `touch-action` CSS property in [Bug > #149854](https://bugs.webkit.org/show_bug.cgi?id=149854). By default, > elements have `touch-action: auto`, which indicates that WebKit may enable > any touch behaviors such as panning, pinching and double-tapping. Putting > `touch-action: manipulation;` on a clickable element makes WebKit consider > touches that begin on the element only for the purposes of panning and > pinching to zoom. This means WebKit does not consider double-tap gestures on > the element, so single taps are dispatched immediately. Single taps on an > element become fast when any of the element’s ancestors have the > `touch-action: manipulation`. Note that putting `touch-action: manipulation` > on any node opts all children of the node into the fast-tap optimization. > > Additionally, single taps on an element with `touch-action: manipulation` are > fast for all zoom scales, whereas our optimizations on device-width viewports > only trigger when the viewport is at initial scale. > > If you have questions, comments or other feedback regarding fast-tapping in > mobile Safari, feel free to reach out to Jon Davis > [@jonathandavis](http://twitter.com/jonathandavis) or WebKit > [@webkit](http://twitter.com/webkit) on Twitter, or email me directly at > [wenson_hs...@apple.com](mailto:wenson_hs...@apple.com). -- Karl Dubost, Mozilla http://www.la-grange.net/karl/moz _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
