September 2020 - Code Heath, Animation Timelines, Smoothness Metrics, Animation event handlers and more!

<td><td>In this sprint we closed a lot of bugs, but more were opened than
closed.</td></td>

<td><td>We now have breakdowns by priority. Nice to see that we did not lose
ground on P0s or P1s.</td></td>

<td><td>setTimeout can easily cause flakiness, especially on debug
bots.</td></td>

<td><td>Animations are driven by animation frames, using rAF leads to more
robust tests.</td></td>

<td><td>The demo illustrates updating the animation timeline via the
web-animation API.</td></td>

<td><td>Presently it is behind the scroll-timeline feature flag.</td></td>

<td><td>The fps meter will reset itself at first contentful paint (which is
regarded as loading completed).</td></td>

<td><td>The stats before first contentful paint will be discarded when we
report to UMA.</td></td>

<td><td>Previously, we compared zoomed values when starting transitions,
then transitionend based on computed value.</td></td>

<td><td>Now we calculate and compare computed values (as per spec) if zoom
changed.</td></td>

Code health

kevers@ presented a graph to show the progress of bug fixing.

xidachen@ removed the usage of setTimeout in animations layout test, and replaced them with rAF.

Mutable timelines

kevers@ has been working on scroll timelines and the above demo showcases mutable timelines, which are required for supporting css animation-timeline.

kevers@ showed another fun demo for scroll timelines, which uses scroll position to drive a paint worklet animation..

Smoothness metrics

xidachen@ improved fps meter by making it account for page loading.

Animation event handlers

gtsteel@ landed the implementation for ontrasition\* event handler properties. Along with that, gtsteel@ also fixed animationcancel event so that it doesn’t fire after animationend.

Zooming no longer breaks transitions

gtsteel@ fixed a bug where zooming would cause transition event listeners to fire.

Web tests ⇒ WPT

liviutinta@ shared a sheet that lists input related layout tests that we would like to move to wpt/. The spreadsheet also tracks the progress.

WebDriver Actions API Spec

lanwei@ has landed spec change that adds wheel input to the webdriver action API.