I think that as it stands, yes, APZ is going to be a "permanent" part of the platform. You're right that having higher-latency scroll events creates some problems and makes it harder to drive animations off it. We do have plans to provide more APIs for controlling things in the compositor which should provide more ways to get to the 60fps goal depending on what you're doing. Implementing CSS animations, scroll snapping, position:sticky etc. in the compositor are examples of what I mean. The Blink guys have been exploring other options as well - things like CompositorWorker [1], where you can have some JS running in the compositor at 60fps doing animations. So yes, there is some ongoing discussion on this topic, but if you have thoughts on this please do let us know.
Cheers, kats [1] e.g. https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/YlG2OvHgVaQ On Sun, Oct 4, 2015 at 2:20 PM, Marcus Cavanaugh <m...@mcav.com> wrote: > APZ is wonderful, making the web feel smooth when a page's demands would > otherwise cause jank. In many cases, it's the *only* reason we're able to > create decent experiences today, particularly on mobile. > > It does, however, highlight a shortcoming of our platform today: we can't > achieve flawless 60fps performance without APZ. We can get close, but any > nontrival-but-reasonable demo will encounter jank, ostensibly due to > compositing and rendering taking too much time. (APZ pathways, rendering > the same content, provide consistent 60fps without frame drops, leading me > to believe that some part of the JS-driven pipeline incurs substantial > cost.) > > This means that on Firefox OS, the only way to achieve buttery-smooth > touch-driven animations is to use overflow-scrollable containers rather > than touch events. Scrollable containers provide a reasonable abstraction > for user-driven fluid touch animations. If we had synchronous control over > scroll events, we could do a lot more with just this; but because of APZ, > we can only do so much: > > On Firefox OS, the "utility tray" (swipe down from the top of the screen) > is now implemented with native scrolling. However, the tray's footer, which > is intended to only appear when the tray reaches the bottom, cannot be > displayed without visual glitches due to APZ -- the user can scroll the > container before JS has a chance to react. > > My question is this: Is APZ intended to be a stopgap measure, to compensate > for platform deficiencies in rendering performance, or is it intended to > become a permanent part of the web? Put another way: Is "onscroll" forever > redefined to be "an estimate of the current scroll position", rather than a > synchronous position callback? (I thought I overheard talk about how > WebRender might obsolete APZ due to its performance, but I may have > misheard.) > > If APZ is with us forever (and 60fps JS-based animation is out of the > question), then I think we need to create an API that allows sites to > provide more fine-grained control over scroll motion. I have more thoughts > on this, if APZ is the way forward. > > I'd also like to better understand why a natively-scrolled container is > able to scroll at 60fps, while the same content scrolled with rAF + > transforms cannot. If the rendered content is the same, where is the > bottleneck? (I can provide test-cases/demos if desired.) I'd like to help > out with addressing this deficiency, but I don't have enough Gecko > experience to know where to begin. > > > Marcus [:mcav] > _______________________________________________ > dev-platform mailing list > dev-platform@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-platform _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
