servo/components/style/style_adjuster.rs

558 lines
22 KiB
Rust

/* 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 http://mozilla.org/MPL/2.0/. */
//! A struct to encapsulate all the style fixups and flags propagations
//! a computed style needs in order for it to adhere to the CSS spec.
use app_units::Au;
use properties::{self, CascadeFlags, ComputedValues};
use properties::{IS_ROOT_ELEMENT, SKIP_ROOT_AND_ITEM_BASED_DISPLAY_FIXUP, StyleBuilder};
use properties::longhands::display::computed_value::T as display;
use properties::longhands::float::computed_value::T as float;
use properties::longhands::overflow_x::computed_value::T as overflow;
use properties::longhands::position::computed_value::T as position;
/// An unsized struct that implements all the adjustment methods.
pub struct StyleAdjuster<'a, 'b: 'a> {
style: &'a mut StyleBuilder<'b>,
}
impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
/// Trivially constructs a new StyleAdjuster.
pub fn new(style: &'a mut StyleBuilder<'b>) -> Self {
StyleAdjuster {
style: style,
}
}
/// https://fullscreen.spec.whatwg.org/#new-stacking-layer
///
/// Any position value other than 'absolute' and 'fixed' are
/// computed to 'absolute' if the element is in a top layer.
///
fn adjust_for_top_layer(&mut self) {
if !self.style.out_of_flow_positioned() && self.style.in_top_layer() {
self.style.mutate_box().set_position(position::absolute);
}
}
/// CSS 2.1 section 9.7:
///
/// If 'position' has the value 'absolute' or 'fixed', [...] the computed
/// value of 'float' is 'none'.
///
fn adjust_for_position(&mut self) {
if self.style.out_of_flow_positioned() && self.style.floated() {
self.style.mutate_box().set_float(float::none);
}
}
/// Apply the blockification rules based on the table in CSS 2.2 section 9.7.
/// https://drafts.csswg.org/css2/visuren.html#dis-pos-flo
fn blockify_if_necessary(&mut self,
layout_parent_style: &ComputedValues,
flags: CascadeFlags) {
let mut blockify = false;
macro_rules! blockify_if {
($if_what:expr) => {
if !blockify {
blockify = $if_what;
}
}
}
if !flags.contains(SKIP_ROOT_AND_ITEM_BASED_DISPLAY_FIXUP) {
blockify_if!(flags.contains(IS_ROOT_ELEMENT));
blockify_if!(layout_parent_style.get_box().clone_display().is_item_container());
}
let is_item_or_root = blockify;
blockify_if!(self.style.floated());
blockify_if!(self.style.out_of_flow_positioned());
if !blockify {
return;
}
let display = self.style.get_box().clone_display();
let blockified_display =
display.equivalent_block_display(flags.contains(IS_ROOT_ELEMENT));
if display != blockified_display {
self.style.mutate_box().set_adjusted_display(blockified_display,
is_item_or_root);
}
}
/// Compute a few common flags for both text and element's style.
pub fn set_bits(&mut self) {
use properties::computed_value_flags::IS_IN_DISPLAY_NONE_SUBTREE;
use properties::computed_value_flags::IS_IN_PSEUDO_ELEMENT_SUBTREE;
if self.style.inherited_flags().contains(IS_IN_DISPLAY_NONE_SUBTREE) ||
self.style.get_box().clone_display() == display::none {
self.style.flags.insert(IS_IN_DISPLAY_NONE_SUBTREE);
}
if self.style.inherited_flags().contains(IS_IN_PSEUDO_ELEMENT_SUBTREE) ||
self.style.is_pseudo_element() {
self.style.flags.insert(IS_IN_PSEUDO_ELEMENT_SUBTREE);
}
}
/// Adjust the style for text style.
///
/// The adjustments here are a subset of the adjustments generally, because
/// text only inherits properties.
///
/// Note that this, for Gecko, comes through Servo_ComputedValues_Inherit.
#[cfg(feature = "gecko")]
pub fn adjust_for_text(&mut self) {
self.adjust_for_text_combine_upright();
self.adjust_for_text_in_ruby();
self.set_bits();
}
/// Change writing mode of the text frame for text-combine-upright.
///
/// It is safe to look at our own style because we are looking at inherited
/// properties, and text is just plain inheritance.
///
/// TODO(emilio): we should (Gecko too) revise these adjustments in presence
/// of display: contents.
#[cfg(feature = "gecko")]
fn adjust_for_text_combine_upright(&mut self) {
use computed_values::text_combine_upright::T as text_combine_upright;
use computed_values::writing_mode::T as writing_mode;
use properties::computed_value_flags::IS_TEXT_COMBINED;
let writing_mode =
self.style.get_inheritedbox().clone_writing_mode();
let text_combine_upright =
self.style.get_inheritedtext().clone_text_combine_upright();
if writing_mode != writing_mode::horizontal_tb &&
text_combine_upright == text_combine_upright::all {
self.style.flags.insert(IS_TEXT_COMBINED);
self.style.mutate_inheritedbox().set_writing_mode(writing_mode::horizontal_tb);
}
}
/// Applies the line break suppression flag to text if it is in any ruby
/// box. This is necessary because its parent may not itself have the flag
/// set (e.g. ruby or ruby containers), thus we may not inherit the flag
/// from them.
#[cfg(feature = "gecko")]
fn adjust_for_text_in_ruby(&mut self) {
use properties::computed_value_flags::SHOULD_SUPPRESS_LINEBREAK;
let parent_display = self.style.get_parent_box().clone_display();
if parent_display.is_ruby_type() {
self.style.flags.insert(SHOULD_SUPPRESS_LINEBREAK);
}
}
/// https://drafts.csswg.org/css-writing-modes-3/#block-flow:
///
/// If a box has a different writing-mode value than its containing
/// block:
///
/// - If the box has a specified display of inline, its display
/// computes to inline-block. [CSS21]
///
/// This matches the adjustment that Gecko does, not exactly following
/// the spec. See also:
///
/// https://lists.w3.org/Archives/Public/www-style/2017Mar/0045.html
/// https://github.com/servo/servo/issues/15754
fn adjust_for_writing_mode(&mut self,
layout_parent_style: &ComputedValues) {
let our_writing_mode = self.style.get_inheritedbox().clone_writing_mode();
let parent_writing_mode = layout_parent_style.get_inheritedbox().clone_writing_mode();
if our_writing_mode != parent_writing_mode &&
self.style.get_box().clone_display() == display::inline {
self.style.mutate_box().set_display(display::inline_block);
}
}
#[cfg(feature = "gecko")]
fn adjust_for_contain(&mut self) {
use properties::longhands::contain;
// An element with contain: paint needs to be a formatting context, and
// also implies overflow: clip.
//
// TODO(emilio): This mimics Gecko, but spec links are missing!
let contain = self.style.get_box().clone_contain();
if !contain.contains(contain::PAINT) {
return;
}
if self.style.get_box().clone_display() == display::inline {
self.style.mutate_box().set_adjusted_display(display::inline_block,
false);
}
// When 'contain: paint', update overflow from 'visible' to 'clip'.
if self.style.get_box().clone_contain().contains(contain::PAINT) {
if self.style.get_box().clone_overflow_x() == overflow::visible {
let box_style = self.style.mutate_box();
box_style.set_overflow_x(overflow::_moz_hidden_unscrollable);
box_style.set_overflow_y(overflow::_moz_hidden_unscrollable);
}
}
}
/// When mathvariant is not "none", font-weight and font-style are
/// both forced to "normal".
#[cfg(feature = "gecko")]
fn adjust_for_mathvariant(&mut self) {
use properties::longhands::_moz_math_variant::computed_value::T as moz_math_variant;
use properties::longhands::font_style::computed_value::T as font_style;
use properties::longhands::font_weight::computed_value::T as font_weight;
if self.style.get_font().clone__moz_math_variant() != moz_math_variant::none {
let font_style = self.style.mutate_font();
// Sadly we don't have a nice name for the computed value
// of "font-weight: normal".
font_style.set_font_weight(font_weight::normal());
font_style.set_font_style(font_style::normal);
}
}
/// This implements an out-of-date spec. The new spec moves the handling of
/// this to layout, which Gecko implements but Servo doesn't.
///
/// See https://github.com/servo/servo/issues/15229
#[cfg(feature = "servo")]
fn adjust_for_alignment(&mut self, layout_parent_style: &ComputedValues) {
use computed_values::align_items::T as align_items;
use computed_values::align_self::T as align_self;
if self.style.get_position().clone_align_self() == align_self::auto &&
!self.style.out_of_flow_positioned() {
let self_align =
match layout_parent_style.get_position().clone_align_items() {
align_items::stretch => align_self::stretch,
align_items::baseline => align_self::baseline,
align_items::flex_start => align_self::flex_start,
align_items::flex_end => align_self::flex_end,
align_items::center => align_self::center,
};
self.style.mutate_position().set_align_self(self_align);
}
}
/// The initial value of border-*-width may be changed at computed value
/// time.
///
/// This is moved to properties.rs for convenience.
fn adjust_for_border_width(&mut self) {
properties::adjust_border_width(self.style);
}
/// The initial value of outline-width may be changed at computed value time.
fn adjust_for_outline(&mut self) {
if self.style.get_outline().clone_outline_style().none_or_hidden() &&
self.style.get_outline().outline_has_nonzero_width() {
self.style.mutate_outline().set_outline_width(Au(0).into());
}
}
/// CSS3 overflow-x and overflow-y require some fixup as well in some
/// cases.
///
/// overflow: clip and overflow: visible are meaningful only when used in
/// both dimensions.
fn adjust_for_overflow(&mut self) {
let original_overflow_x = self.style.get_box().clone_overflow_x();
let original_overflow_y = self.style.get_box().clone_overflow_y();
let mut overflow_x = original_overflow_x;
let mut overflow_y = original_overflow_y;
if overflow_x == overflow_y {
return;
}
// If 'visible' is specified but doesn't match the other dimension,
// it turns into 'auto'.
if overflow_x == overflow::visible {
overflow_x = overflow::auto;
}
if overflow_y == overflow::visible {
overflow_y = overflow::auto;
}
#[cfg(feature = "gecko")]
{
// overflow: clip is deprecated, so convert to hidden if it's
// specified in only one dimension.
if overflow_x == overflow::_moz_hidden_unscrollable {
overflow_x = overflow::hidden;
}
if overflow_y == overflow::_moz_hidden_unscrollable {
overflow_y = overflow::hidden;
}
}
if overflow_x != original_overflow_x ||
overflow_y != original_overflow_y {
let box_style = self.style.mutate_box();
box_style.set_overflow_x(overflow_x);
box_style.set_overflow_y(overflow_y);
}
}
/// Native anonymous content converts display:contents into display:inline.
#[cfg(feature = "gecko")]
fn adjust_for_prohibited_display_contents(&mut self, flags: CascadeFlags) {
use properties::PROHIBIT_DISPLAY_CONTENTS;
// TODO: We should probably convert display:contents into display:none
// in some cases too: https://drafts.csswg.org/css-display/#unbox
if !flags.contains(PROHIBIT_DISPLAY_CONTENTS) ||
self.style.get_box().clone_display() != display::contents {
return;
}
self.style.mutate_box().set_display(display::inline);
}
/// If a <fieldset> has grid/flex display type, we need to inherit
/// this type into its ::-moz-fieldset-content anonymous box.
#[cfg(feature = "gecko")]
fn adjust_for_fieldset_content(&mut self,
layout_parent_style: &ComputedValues,
flags: CascadeFlags) {
use properties::IS_FIELDSET_CONTENT;
if !flags.contains(IS_FIELDSET_CONTENT) {
return;
}
debug_assert_eq!(self.style.get_box().clone_display(), display::block);
// TODO We actually want style from parent rather than layout
// parent, so that this fixup doesn't happen incorrectly when
// when <fieldset> has "display: contents".
let parent_display = layout_parent_style.get_box().clone_display();
let new_display = match parent_display {
display::flex | display::inline_flex => Some(display::flex),
display::grid | display::inline_grid => Some(display::grid),
_ => None,
};
if let Some(new_display) = new_display {
self.style.mutate_box().set_display(new_display);
}
}
/// -moz-center, -moz-left and -moz-right are used for HTML's alignment.
///
/// This is covering the <div align="right"><table>...</table></div> case.
///
/// In this case, we don't want to inherit the text alignment into the
/// table.
#[cfg(feature = "gecko")]
fn adjust_for_table_text_align(&mut self) {
use properties::longhands::text_align::computed_value::T as text_align;
if self.style.get_box().clone_display() != display::table {
return;
}
match self.style.get_inheritedtext().clone_text_align() {
text_align::_moz_left |
text_align::_moz_center |
text_align::_moz_right => {}
_ => return,
}
self.style.mutate_inheritedtext().set_text_align(text_align::start);
}
/// Set the HAS_TEXT_DECORATION_LINES flag based on parent style.
fn adjust_for_text_decoration_lines(&mut self, layout_parent_style: &ComputedValues) {
use properties::computed_value_flags::HAS_TEXT_DECORATION_LINES;
if layout_parent_style.flags.contains(HAS_TEXT_DECORATION_LINES) ||
!self.style.get_text().clone_text_decoration_line().is_empty() {
self.style.flags.insert(HAS_TEXT_DECORATION_LINES);
}
}
#[cfg(feature = "gecko")]
fn should_suppress_linebreak(&self, layout_parent_style: &ComputedValues) -> bool {
use properties::computed_value_flags::SHOULD_SUPPRESS_LINEBREAK;
// Line break suppression should only be propagated to in-flow children.
if self.style.floated() || self.style.out_of_flow_positioned() {
return false;
}
let parent_display = layout_parent_style.get_box().clone_display();
if layout_parent_style.flags.contains(SHOULD_SUPPRESS_LINEBREAK) {
// Line break suppression is propagated to any children of
// line participants.
if parent_display.is_line_participant() {
return true;
}
}
match self.style.get_box().clone_display() {
// Ruby base and text are always non-breakable.
display::ruby_base | display::ruby_text => true,
// Ruby base container and text container are breakable.
// Note that, when certain HTML tags, e.g. form controls, have ruby
// level container display type, they could also escape from the
// line break suppression flag while they shouldn't. However, it is
// generally fine since they themselves are non-breakable.
display::ruby_base_container | display::ruby_text_container => false,
// Anything else is non-breakable if and only if its layout parent
// has a ruby display type, because any of the ruby boxes can be
// anonymous.
_ => parent_display.is_ruby_type(),
}
}
/// Do ruby-related style adjustments, which include:
/// * propagate the line break suppression flag,
/// * inlinify block descendants,
/// * suppress border and padding for ruby level containers,
/// * correct unicode-bidi.
#[cfg(feature = "gecko")]
fn adjust_for_ruby(&mut self,
layout_parent_style: &ComputedValues,
flags: CascadeFlags) {
use properties::SKIP_ROOT_AND_ITEM_BASED_DISPLAY_FIXUP;
use properties::computed_value_flags::SHOULD_SUPPRESS_LINEBREAK;
use properties::longhands::unicode_bidi::computed_value::T as unicode_bidi;
let self_display = self.style.get_box().clone_display();
// Check whether line break should be suppressed for this element.
if self.should_suppress_linebreak(layout_parent_style) {
self.style.flags.insert(SHOULD_SUPPRESS_LINEBREAK);
// Inlinify the display type if allowed.
if !flags.contains(SKIP_ROOT_AND_ITEM_BASED_DISPLAY_FIXUP) {
let inline_display = self_display.inlinify();
if self_display != inline_display {
self.style.mutate_box().set_display(inline_display);
}
}
}
// Suppress border and padding for ruby level containers.
// This is actually not part of the spec. It is currently unspecified
// how border and padding should be handled for ruby level container,
// and suppressing them here make it easier for layout to handle.
if self_display.is_ruby_level_container() {
self.style.reset_border_struct();
self.style.reset_padding_struct();
}
// Force bidi isolation on all internal ruby boxes and ruby container
// per spec https://drafts.csswg.org/css-ruby-1/#bidi
if self_display.is_ruby_type() {
let new_value = match self.style.get_text().clone_unicode_bidi() {
unicode_bidi::normal | unicode_bidi::embed => Some(unicode_bidi::isolate),
unicode_bidi::bidi_override => Some(unicode_bidi::isolate_override),
_ => None,
};
if let Some(new_value) = new_value {
self.style.mutate_text().set_unicode_bidi(new_value);
}
}
}
/// Computes the RELEVANT_LINK_VISITED flag based on the parent style and on
/// whether we're a relevant link.
///
/// NOTE(emilio): We don't do this for text styles, which is... dubious, but
/// Gecko doesn't seem to do it either. It's extremely easy to do if needed
/// though.
///
/// FIXME(emilio): This isn't technically a style adjustment thingie, could
/// it move somewhere else?
fn adjust_for_visited(&mut self, flags: CascadeFlags) {
use properties::{IS_LINK, IS_VISITED_LINK};
use properties::computed_value_flags::IS_RELEVANT_LINK_VISITED;
if !self.style.has_visited_style() {
return;
}
let relevant_link_visited = if flags.contains(IS_LINK) {
flags.contains(IS_VISITED_LINK)
} else {
self.style.inherited_flags().contains(IS_RELEVANT_LINK_VISITED)
};
if relevant_link_visited {
self.style.flags.insert(IS_RELEVANT_LINK_VISITED);
}
}
/// Resolves "justify-items: auto" based on the inherited style if needed to
/// comply with:
///
/// https://drafts.csswg.org/css-align/#valdef-justify-items-legacy
///
/// (Note that "auto" is being renamed to "legacy")
#[cfg(feature = "gecko")]
fn adjust_for_justify_items(&mut self) {
use values::specified::align;
let justify_items = self.style.get_position().clone_justify_items();
if justify_items.specified.0 != align::ALIGN_AUTO {
return;
}
let parent_justify_items =
self.style.get_parent_position().clone_justify_items();
if !parent_justify_items.computed.0.contains(align::ALIGN_LEGACY) {
return;
}
if parent_justify_items.computed == justify_items.computed {
return;
}
self.style
.mutate_position()
.set_computed_justify_items(parent_justify_items.computed);
}
/// Adjusts the style to account for various fixups that don't fit naturally
/// into the cascade.
///
/// When comparing to Gecko, this is similar to the work done by
/// `nsStyleContext::ApplyStyleFixups`, plus some parts of
/// `nsStyleSet::GetContext`.
pub fn adjust(&mut self,
layout_parent_style: &ComputedValues,
flags: CascadeFlags) {
self.adjust_for_visited(flags);
#[cfg(feature = "gecko")]
{
self.adjust_for_prohibited_display_contents(flags);
self.adjust_for_fieldset_content(layout_parent_style, flags);
}
self.adjust_for_top_layer();
self.blockify_if_necessary(layout_parent_style, flags);
self.adjust_for_position();
self.adjust_for_overflow();
#[cfg(feature = "gecko")]
{
self.adjust_for_table_text_align();
self.adjust_for_contain();
self.adjust_for_mathvariant();
self.adjust_for_justify_items();
}
#[cfg(feature = "servo")]
{
self.adjust_for_alignment(layout_parent_style);
}
self.adjust_for_border_width();
self.adjust_for_outline();
self.adjust_for_writing_mode(layout_parent_style);
self.adjust_for_text_decoration_lines(layout_parent_style);
#[cfg(feature = "gecko")]
{
self.adjust_for_ruby(layout_parent_style, flags);
}
self.set_bits();
}
}