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style: Implement Animate for track lists on grid-template-{columns|ro…

…ws}.

Based on https://bugzilla.mozilla.org/show_bug.cgi?id=1348519#c6 and
w3c/csswg-drafts#3201:

Currently grid-template-rows/columns interpolate “per computed value”, which
means that if the number of tracks differs, or any track changes to/from a
particular keyword value to any other value, or if a line name is added/removed
at any position, the entire track listing is interpolated as “discrete”.
But we "agree" with two more granular options:

1. Check interpolation type per track, rather than for the entire list, before
   falling back to discrete. I.e. a length-percentage track can animate between
   two values while an adjacent auto track flips discretely to min-content.
2. Allow discrete interpolation of line name changes independently of track
   sizes.

Besides, for the repeat() function, it's complicated to support interpolation
between different repeat types (i.e. auto-fill, auto-fit) and different repeat
counts, so we always fall-back to discrete if the first parameter of repeat()
is different.

Differential Revision: https://phabricator.services.mozilla.com/D16129
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BorisChiou authored and emilio committed Jan 12, 2019
1 parent a8943d2 commit 2b77a29697840f64201f6a5a3080dbdfb83ac9eb
@@ -383,7 +383,7 @@ ${helpers.predefined_type(
spec="https://drafts.csswg.org/css-grid/#propdef-grid-template-%ss" % kind,
boxed=True,
flags="GETCS_NEEDS_LAYOUT_FLUSH",
animation_value_type="discrete",
animation_value_type="ComputedValue",
)}

% endfor
@@ -0,0 +1,153 @@
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */

//! Animation implementation for various grid-related types.

// Note: we can implement Animate on their generic types directly, but in this case we need to
// make sure two trait bounds, L: Clone and I: PartialEq, are satisfied on almost all the
// grid-related types and their other trait implementations because Animate needs them. So in
// order to avoid adding these two trait bounds (or maybe more..) everywhere, we implement
// Animate for the computed types, instead of the generic types.

use super::{Animate, Procedure, ToAnimatedZero};
use crate::values::computed::{GridTemplateComponent, TrackList, TrackSize};
use crate::values::computed::Integer;
use crate::values::computed::LengthPercentage;
use crate::values::distance::{ComputeSquaredDistance, SquaredDistance};
use crate::values::generics::grid as generics;

fn discrete<T: Clone>(from: &T, to: &T, procedure: Procedure) -> Result<T, ()> {
if let Procedure::Interpolate { progress } = procedure {
Ok(if progress < 0.5 { from.clone() } else { to.clone() })
} else {
Err(())
}
}

fn animate_with_discrete_fallback<T: Animate + Clone>(
from: &T,
to: &T,
procedure: Procedure
) -> Result<T, ()> {
from.animate(to, procedure).or_else(|_| discrete(from, to, procedure))
}

impl Animate for TrackSize {
fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
match (self, other) {
(&generics::TrackSize::Breadth(ref from),
&generics::TrackSize::Breadth(ref to)) => {
animate_with_discrete_fallback(from, to, procedure)
.map(generics::TrackSize::Breadth)
},
(&generics::TrackSize::Minmax(ref from_min, ref from_max),
&generics::TrackSize::Minmax(ref to_min, ref to_max)) => {
Ok(generics::TrackSize::Minmax(
animate_with_discrete_fallback(from_min, to_min, procedure)?,
animate_with_discrete_fallback(from_max, to_max, procedure)?,
))
},
(&generics::TrackSize::FitContent(ref from),
&generics::TrackSize::FitContent(ref to)) => {
animate_with_discrete_fallback(from, to, procedure)
.map(generics::TrackSize::FitContent)
},
(_, _) => discrete(self, other, procedure),
}
}
}

impl Animate for generics::TrackRepeat<LengthPercentage, Integer>
where
generics::RepeatCount<Integer>: PartialEq,
{
fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
// If the keyword, auto-fit/fill, is the same it can result in different
// number of tracks. For both auto-fit/fill, the number of columns isn't
// known until you do layout since it depends on the container size, item
// placement and other factors, so we cannot do the correct interpolation
// by computed values. Therefore, return Err(()) if it's keywords. If it
// is Number, we support animation only if the count is the same and the
// length of track_sizes is the same.
// https://github.com/w3c/csswg-drafts/issues/3503
match (&self.count, &other.count) {
(&generics::RepeatCount::Number(from),
&generics::RepeatCount::Number(to)) if from == to => (),
(_, _) => return Err(()),
}

// The length of track_sizes should be matched.
if self.track_sizes.len() != other.track_sizes.len() {
return Err(());
}

let count = self.count;
let track_sizes = self.track_sizes
.iter()
.zip(other.track_sizes.iter())
.map(|(a, b)| a.animate(b, procedure))
.collect::<Result<Vec<_>, _>>()?;

// The length of |line_names| is always 0 or N+1, where N is the length
// of |track_sizes|. Besides, <line-names> is always discrete.
let line_names = discrete(&self.line_names, &other.line_names, procedure)?;

Ok(generics::TrackRepeat { count, line_names, track_sizes })
}
}

impl Animate for TrackList {
// Based on https://github.com/w3c/csswg-drafts/issues/3201:
// 1. Check interpolation type per track, so we need to handle discrete animations
// in TrackSize, so any Err(()) returned from TrackSize doesn't make all TrackSize
// fallback to discrete animation.
// 2. line-names is always discrete.
fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
if self.values.len() != other.values.len() {
return Err(());
}

if self.list_type != other.list_type {
return Err(());
}

// For now, repeat(auto-fill/auto-fit, ...) is not animatable. TrackRepeat will
// return Err(()) if we use keywords. Therefore, we can early return here to avoid
// traversing |values| in <auto-track-list>. This may be updated in the future.
// https://github.com/w3c/csswg-drafts/issues/3503
if let generics::TrackListType::Auto(_) = self.list_type {
return Err(());
}

let list_type = self.list_type;
let auto_repeat = self.auto_repeat.animate(&other.auto_repeat, procedure)?;
let values = self.values
.iter()
.zip(other.values.iter())
.map(|(a, b)| a.animate(b, procedure))
.collect::<Result<Vec<_>, _>>()?;
// The length of |line_names| is always 0 or N+1, where N is the length
// of |track_sizes|. Besides, <line-names> is always discrete.
let line_names = discrete(&self.line_names, &other.line_names, procedure)?;

Ok(TrackList { list_type, values, line_names, auto_repeat })
}
}

impl ComputeSquaredDistance for GridTemplateComponent {
#[inline]
fn compute_squared_distance(&self, _other: &Self) -> Result<SquaredDistance, ()> {
// TODO: Bug 1518585, we should implement ComputeSquaredDistance.
Err(())
}
}

impl ToAnimatedZero for GridTemplateComponent {
#[inline]
fn to_animated_zero(&self) -> Result<Self, ()> {
// It's not clear to get a zero grid track list based on the current definition
// of spec, so we return Err(()) directly.
Err(())
}
}
@@ -23,6 +23,7 @@ use std::cmp;
pub mod color;
pub mod effects;
mod font;
mod grid;
mod length;
mod svg;
pub mod transform;
@@ -151,6 +151,7 @@ impl Parse for GridLine<specified::Integer> {
#[allow(missing_docs)]
#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
#[derive(
Animate,
Clone,
Copy,
Debug,
@@ -172,7 +173,16 @@ pub enum TrackKeyword {
/// avoid re-implementing it for the computed type.
///
/// <https://drafts.csswg.org/css-grid/#typedef-track-breadth>
#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
#[derive(
Animate,
Clone,
Debug,
MallocSizeOf,
PartialEq,
SpecifiedValueInfo,
ToComputedValue,
ToCss,
)]
pub enum TrackBreadth<L> {
/// The generic type is almost always a non-negative `<length-percentage>`
Breadth(L),
@@ -481,12 +491,21 @@ impl<L: Clone> TrackRepeat<L, specified::Integer> {
}

/// Track list values. Can be <track-size> or <track-repeat>
#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
#[derive(
Animate,
Clone,
Debug,
MallocSizeOf,
PartialEq,
SpecifiedValueInfo,
ToComputedValue,
ToCss
)]
pub enum TrackListValue<LengthPercentage, Integer> {
/// A <track-size> value.
TrackSize(TrackSize<LengthPercentage>),
TrackSize(#[animation(field_bound)] TrackSize<LengthPercentage>),
/// A <track-repeat> value.
TrackRepeat(TrackRepeat<LengthPercentage, Integer>),
TrackRepeat(#[animation(field_bound)] TrackRepeat<LengthPercentage, Integer>),
}

/// The type of a `<track-list>` as determined during parsing.
@@ -692,13 +711,24 @@ impl ToCss for LineNameList {
/// Variants for `<grid-template-rows> | <grid-template-columns>`
/// Subgrid deferred to Level 2 spec due to lack of implementation.
/// But it's implemented in gecko, so we have to as well.
#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
#[derive(
Animate,
Clone,
Debug,
MallocSizeOf,
PartialEq,
SpecifiedValueInfo,
ToComputedValue,
ToCss
)]
pub enum GridTemplateComponent<L, I> {
/// `none` value.
None,
/// The grid `<track-list>`
TrackList(#[compute(field_bound)] TrackList<L, I>),
TrackList(#[animation(field_bound)] #[compute(field_bound)] TrackList<L, I>),
/// A `subgrid <line-name-list>?`
/// TODO: Support animations for this after subgrid is addressed in [grid-2] spec.
#[animation(error)]
Subgrid(LineNameList),
}

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