servo/components/style/values/generics/font.rs
Jon Leighton 691c6c6f1a Implement font fallback
Prior to this change, if none of the fonts specified in CSS contained a
glyph for a codepoint, we tried only one fallback font. If that font
didn't contain the glyph, we'd give up.

With this change, we try multiple fonts in turn. The font names we try
differ across each platform, and based on the codepoint we're trying to
match. The current implementation is heavily inspired by the analogous
code in Gecko, but I've used to ucd lib to make it more readable,
whereas Gecko matches raw unicode ranges.

This fixes some of the issues reported in #17267, although colour emoji
support is not implemented.

== Notes on changes to WPT metadata ==

=== css/css-text/i18n/css3-text-line-break-opclns-* ===

A bunch of these have started failing on macos when they previously
passed.

These tests check that the browser automatically inserts line breaks
near certain characters that are classified as "opening and closing
punctuation". The idea is that if we have e.g. an opening parenthesis,
it does not make sense for it to appear at the end of a line box; it
should "stick" to the next character and go into the next line box.

Before this change, a lot of these codepoints rendered as a missing
glyph on Mac and Linux. In some cases, that meant that the test was
passing.

After this change, a bunch of these codepoints are now rendering glyphs
on Mac (but not Linux). In some cases, the test should continue to pass
where it previously did when rendering with the missing glyph.

However, it seems this has also exposed a layout bug. The "ref" div in
these tests contains a <br> element, and it seems that this, combined
with these punctuation characters, makes the spacing between glyphs ever
so slightly different to the "test" div. (Speculation: might be
something to do with shaping?)

Therefore I've had to mark a bunch of these tests failing on mac.

=== css/css-text/i18n/css3-text-line-break-baspglwj-* ===

Some of these previously passed on Mac due to a missing glyph. Now that
we're rendering the correct glyph, they are failing.

=== css/css-text/word-break/word-break-normal-bo-000.html ===

The characters now render correctly on Mac, and the test is passing. But
we do not find a suitable fallback font on Linux, so it is still failing
on that platform.

=== css/css-text/word-break/word-break-break-all-007.html ===

This was previously passing on Mac, but only because missing character
glyphs were rendered. Now that a fallback font is able to be found, it
(correctly) fails.

=== mozilla/tests/css/font_fallback_* ===

These are new tests added in this commit. 01 and 02 are marked failing
on Linux because the builders don't have the appropriate fonts installed
(that will be a follow-up).

Fix build errors from rebase

FontTemplateDescriptor can no longer just derive(Hash). We need to
implement it on each component part, because the components now
generally wrap floats, which do not impl Hash because of NaN. However in
this case we know that we won't have a NaN, so it is safe to manually
impl Hash.
2018-05-19 14:33:36 +10:00

240 lines
6.8 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/. */
//! Generic types for font stuff.
use app_units::Au;
use byteorder::{BigEndian, ReadBytesExt};
use cssparser::Parser;
use num_traits::One;
use parser::{Parse, ParserContext};
use std::fmt::{self, Write};
use std::io::Cursor;
use style_traits::{CssWriter, KeywordsCollectFn, ParseError};
use style_traits::{SpecifiedValueInfo, StyleParseErrorKind, ToCss};
use values::distance::{ComputeSquaredDistance, SquaredDistance};
/// https://drafts.csswg.org/css-fonts-4/#feature-tag-value
#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
ToComputedValue)]
pub struct FeatureTagValue<Integer> {
/// A four-character tag, packed into a u32 (one byte per character).
pub tag: FontTag,
/// The actual value.
pub value: Integer,
}
impl<Integer> ToCss for FeatureTagValue<Integer>
where
Integer: One + ToCss + PartialEq,
{
fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
where
W: Write,
{
self.tag.to_css(dest)?;
// Don't serialize the default value.
if self.value != Integer::one() {
dest.write_char(' ')?;
self.value.to_css(dest)?;
}
Ok(())
}
}
/// Variation setting for a single feature, see:
///
/// https://drafts.csswg.org/css-fonts-4/#font-variation-settings-def
#[derive(Animate, Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
ToComputedValue, ToCss)]
pub struct VariationValue<Number> {
/// A four-character tag, packed into a u32 (one byte per character).
#[animation(constant)]
pub tag: FontTag,
/// The actual value.
pub value: Number,
}
impl<Number> ComputeSquaredDistance for VariationValue<Number>
where
Number: ComputeSquaredDistance,
{
#[inline]
fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
if self.tag != other.tag {
return Err(());
}
self.value.compute_squared_distance(&other.value)
}
}
/// A value both for font-variation-settings and font-feature-settings.
#[css(comma)]
#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
ToComputedValue, ToCss)]
pub struct FontSettings<T>(#[css(if_empty = "normal", iterable)] pub Box<[T]>);
impl<T> FontSettings<T> {
/// Default value of font settings as `normal`.
#[inline]
pub fn normal() -> Self {
FontSettings(vec![].into_boxed_slice())
}
}
impl<T: Parse> Parse for FontSettings<T> {
/// https://drafts.csswg.org/css-fonts-4/#descdef-font-face-font-feature-settings
/// https://drafts.csswg.org/css-fonts-4/#font-variation-settings-def
fn parse<'i, 't>(
context: &ParserContext,
input: &mut Parser<'i, 't>,
) -> Result<Self, ParseError<'i>> {
if input.try(|i| i.expect_ident_matching("normal")).is_ok() {
return Ok(Self::normal());
}
Ok(FontSettings(
input
.parse_comma_separated(|i| T::parse(context, i))?
.into_boxed_slice(),
))
}
}
/// A font four-character tag, represented as a u32 for convenience.
///
/// See:
/// https://drafts.csswg.org/css-fonts-4/#font-variation-settings-def
/// https://drafts.csswg.org/css-fonts-4/#descdef-font-face-font-feature-settings
///
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
ToComputedValue)]
pub struct FontTag(pub u32);
impl ToCss for FontTag {
fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
where
W: Write,
{
use byteorder::{BigEndian, ByteOrder};
use std::str;
let mut raw = [0u8; 4];
BigEndian::write_u32(&mut raw, self.0);
str::from_utf8(&raw).unwrap_or_default().to_css(dest)
}
}
impl Parse for FontTag {
fn parse<'i, 't>(
_context: &ParserContext,
input: &mut Parser<'i, 't>,
) -> Result<Self, ParseError<'i>> {
let location = input.current_source_location();
let tag = input.expect_string()?;
// allowed strings of length 4 containing chars: <U+20, U+7E>
if tag.len() != 4 || tag.as_bytes().iter().any(|c| *c < b' ' || *c > b'~') {
return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
}
let mut raw = Cursor::new(tag.as_bytes());
Ok(FontTag(raw.read_u32::<BigEndian>().unwrap()))
}
}
#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
ToAnimatedValue, ToAnimatedZero, ToCss)]
/// Additional information for keyword-derived font sizes.
pub struct KeywordInfo<Length> {
/// The keyword used
pub kw: KeywordSize,
/// A factor to be multiplied by the computed size of the keyword
#[css(skip)]
pub factor: f32,
/// An additional Au offset to add to the kw*factor in the case of calcs
#[css(skip)]
pub offset: Length,
}
impl<L> KeywordInfo<L>
where
Au: Into<L>,
{
/// KeywordInfo value for font-size: medium
pub fn medium() -> Self {
KeywordSize::Medium.into()
}
}
impl<L> From<KeywordSize> for KeywordInfo<L>
where
Au: Into<L>,
{
fn from(x: KeywordSize) -> Self {
KeywordInfo {
kw: x,
factor: 1.,
offset: Au(0).into(),
}
}
}
impl<L> SpecifiedValueInfo for KeywordInfo<L> {
fn collect_completion_keywords(f: KeywordsCollectFn) {
<KeywordSize as SpecifiedValueInfo>::collect_completion_keywords(f);
}
}
/// CSS font keywords
#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
Parse, PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero,
ToCss)]
#[allow(missing_docs)]
pub enum KeywordSize {
#[css(keyword = "xx-small")]
XXSmall,
XSmall,
Small,
Medium,
Large,
XLarge,
#[css(keyword = "xx-large")]
XXLarge,
// This is not a real font keyword and will not parse
// HTML font-size 7 corresponds to this value
#[css(skip)]
XXXLarge,
}
impl KeywordSize {
/// Convert to an HTML <font size> value
#[inline]
pub fn html_size(self) -> u8 {
self as u8
}
}
impl Default for KeywordSize {
fn default() -> Self {
KeywordSize::Medium
}
}
/// A generic value for the `font-style` property.
///
/// https://drafts.csswg.org/css-fonts-4/#font-style-prop
#[allow(missing_docs)]
#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, Hash, MallocSizeOf,
PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero)]
pub enum FontStyle<Angle> {
#[animation(error)]
Normal,
#[animation(error)]
Italic,
#[value_info(starts_with_keyword)]
Oblique(Angle),
}