The CSS Timing spec has finally been updated to include the replacement to the previously specced frames() timing function:https://drafts.csswg.org/css-timing-1/#step-timing-functionsBasically it consists of four new step position keywords: jump-start jump-end jump-none jump-bothThe first two are mostly aliases but at least 'jump-start' will need to be preserved as a separate keyword to 'start' so that they serialize differently. Both 'jump-end' and 'end' are not serialized so we don't need to preserve that distinction.We should drop our implementation of frames() and add these keywords instead.

Maybe I have time to work on this, given my other bugs have some spec issues.

Note that the CSS Timing Functions spec has just been renamed to CSS Easing Functions so if there are links to css-timing in tests and so on, it might be worthwhile to update them to css-easing while we're touching those files.https://drafts.csswg.org/css-easing/

(In reply to Brian Birtles (:birtles) fromcomment #2)> Note that the CSS Timing Functions spec has just been renamed to CSS Easing> Functions so if there are links to css-timing in tests and so on, it might> be worthwhile to update them to css-easing while we're touching those files.> >https://drafts.csswg.org/css-easing/One of my patch will rename this. Besides, I'm start to think is it possible to drop/simplify the conversion between computed::TimingFunction and nsTimingFunction (i.e. gecko_bindings/sugar/ns_timing_function.rs)? Maybe we could do that after [1] is merged into cbindgen.[1]https://github.com/eqrion/cbindgen/pull/219

frames() timing function was removed from the spec, so we drop it.Besides, some devtool tests are removed because they use frame(). I willadd them back by using new step function later.

Rename css-timing to css-easing according to the spec update.Depends on D9309

TimingFunction is defined in a separate spec (i.e. css-easing), insteadof transform, so we move it into a different file.Depends on D9310

So we can generate generic enum by cbindgen (for TimingFunction).Depends on D9311

First, we generate StyleComputedTimingFunction by cbindgen from Rust, and useit in nsTimingFunction, so we could copy it directly without handlingthe different memory layout. However, we have to rewrite thensTimingFunction and mozilla::ComputedTimingFunction for this.Second, the rust-bindgen seems cannot generate the correct generic membersfrom complex C++ templates, especially for the nested template struct:e.g.template<A, B>union Foo { struct Bar1 { A mA; }; struct Bar2 { B mB; }; Bar1 bar1; Bar2 bar2;};The generated rust code may look like:pub struct Foo<A, B> { // Foo_Bar1_Body should have one template parameter. pub bar1: root::__BindgenUnionField<root::Foo_Bar1_Body>, // Foo_Bar2_Body should have one template parameter. pub bar2: root::__BindgenUnionField<root::Foo_Bar2_Body>,}pub struct Foo_Bar1_Body<A> { ... }pub struct Foo_Bar2_Body<B> { ... }So we have to hide StyleTimingFunction to avoid the compilation errors.Depends on D9312

1. Add a new preference, layout.css.step-position-jump.enabled, for step(_, jump-*) timing functions.2. We still keep Start and End tags, even though there is no difference between them. Therefore, we could disable the preference if needed.3. Update the calculation of StepTiming to match the algorithm in the spec.Depends on D9313

Add new mochitests, and web-platform tests, and devtool tests.Depends on D9314

We make sure the step number is always positive, so usingcomputed::Integer is safe and can derive ToComputedValue.Depends on D9311

try:https://treeherder.mozilla.org/#/jobs?repo=try&revision=9efcc34814539f4650d38625dacd9baaae212e59

try:https://treeherder.mozilla.org/#/jobs?repo=try&revision=b2d7e0457825aa9843a5cb85948daa66a490984c

Pushed bybchiou@mozilla.com:https://hg.mozilla.org/integration/autoland/rev/b46aa2883e42Part 1: Drop frames() timing function r=birtleshttps://hg.mozilla.org/integration/autoland/rev/e9bf605e24a2Part 2: Rename css-timing to css-easing r=birtleshttps://hg.mozilla.org/integration/autoland/rev/dca7e62232c1Part 3: Split TimingFunction into a separate file to match spec r=emiliohttps://hg.mozilla.org/integration/autoland/rev/d6e5970c62bePart 4: Replace u32 with computed::Integer for computed::TimingFunction r=emiliohttps://hg.mozilla.org/integration/autoland/rev/5b744b960fe0Part 5: Bump cbindgen to 0.6.6 r=emiliohttps://hg.mozilla.org/integration/autoland/rev/79675a8112d6part 6: Generate StyleTimingFunction and drop ns_timing_function.rs r=emilio,birtleshttps://hg.mozilla.org/integration/autoland/rev/77d9e79ed3b9part 7: Implement steps(jump-*) functions r=birtleshttps://hg.mozilla.org/integration/autoland/rev/24936aee7543part 8: Tests r=birtles

Pushed byemilio@crisal.io:https://hg.mozilla.org/integration/mozilla-inbound/rev/cd47bdbd4efaUpdate min cbindgen version in osx.py.

Pushed byrgurzau@mozilla.com:https://hg.mozilla.org/mozilla-central/rev/6771e96bb376Update min cbindgen version in osx.py. a=emilio

(In reply to Pulsebot fromcomment #16)> Pushed byemilio@crisal.io:>https://hg.mozilla.org/integration/mozilla-inbound/rev/cd47bdbd4efa> Update min cbindgen version in osx.pyThanks for this!

Looks like the test changes didn't get upstreamed. Filedbug 1502788 for that.

Created web-platform-tests PRhttps://github.com/web-platform-tests/wpt/pull/13868 for changes under testing/web-platform/tests

Upstream PR merged

Note to MDN writers:I have added a note to the Fx65 rel notes to cover this (two actually):https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/65#CSSIn terms of the documentation, there are a number of places this is mentioned that will need to be updated to remove mention of frames(), and add in description of the new keywords and how they are used:https://developer.mozilla.org/en-US/docs/Web/CSS/transition-timing-functionhttps://developer.mozilla.org/en-US/docs/Web/CSS/animation-timing-functionhttps://developer.mozilla.org/en-US/docs/Web/CSS/single-transition-timing-functionhttps://developer.mozilla.org/en-US/docs/Web/CSS/animationhttps://developer.mozilla.org/en-US/docs/Web/CSS/transitionSyntax in the MDN data repo and browser compat data will also need updating.For the spec definitions, see:https://drafts.csswg.org/css-easing-1/#step-timing-functions