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style: Implement steps(jump-*) functions.

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1. Add a new preference, layout.css.step-position-jump.enabled, for
   step(_, jump-*) timing functions.
2. We still keep JumpEnd 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.
4. For servo, we implement the correct step function algorithm except
   for the handling of before_flag. This could be fixed later.

Depends on D9313

Differential Revision: https://phabricator.services.mozilla.com/D9314
This commit is contained in:
Boris Chiou 2018-10-26 18:03:37 +00:00 • committed by Emilio Cobos Álvarez
parent 3723042937
commit 0c057d9299
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GPG key ID: 056B727BB9C1027C
3 changed files with 67 additions and 8 deletions
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25
components/style/values/generics/easing.rs
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@ -6,6 +6,7 @@
//! https://drafts.csswg.org/css-easing/#timing-functions
use values::CSSFloat;
use parser::ParserContext;
/// A generic easing function.
#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
@ -23,7 +24,8 @@ pub enum TimingFunction<Integer, Number> {
x2: Number,
y2: Number,
},
/// `step-start | step-end | steps(<integer>, [ start | end ]?)`
/// `step-start | step-end | steps(<integer>, [ <step-position> ]?)`
/// `<step-position> = jump-start | jump-end | jump-none | jump-both | start | end`
#[css(comma, function)]
#[value_info(other_values = "step-start,step-end")]
Steps(Integer, #[css(skip_if = "is_end")] StepPosition),
@ -52,18 +54,37 @@ pub enum TimingKeyword {
EaseInOut,
}
#[cfg(feature = "gecko")]
fn step_position_jump_enabled(_context: &ParserContext) -> bool {
use gecko_bindings::structs;
unsafe { structs::StaticPrefs_sVarCache_layout_css_step_position_jump_enabled }
}
#[cfg(feature = "servo")]
fn step_position_jump_enabled(_context: &ParserContext) -> bool {
false
}
#[allow(missing_docs)]
#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
#[repr(u8)]
pub enum StepPosition {
#[parse(condition = "step_position_jump_enabled")]
JumpStart,
#[parse(condition = "step_position_jump_enabled")]
JumpEnd,
#[parse(condition = "step_position_jump_enabled")]
JumpNone,
#[parse(condition = "step_position_jump_enabled")]
JumpBoth,
Start,
End,
}
#[inline]
fn is_end(position: &StepPosition) -> bool {
*position == StepPosition::End
*position == StepPosition::JumpEnd || *position == StepPosition::End
}
impl<Integer, Number> TimingFunction<Integer, Number> {