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style: Use horizontal metrics for ch in vertical mixed/sideways writing modes and for ex always.

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Differential Revision: https://phabricator.services.mozilla.com/D23426
This commit is contained in:
Cameron McCormack 2019-03-21 04:50:47 +00:00 • committed by Emilio Cobos Álvarez
parent d5f208e18c
commit d4635f1d12
3 changed files with 42 additions and 8 deletions
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28
components/style/values/specified/length.rs
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@ -7,7 +7,7 @@
//! [length]: https://drafts.csswg.org/css-values/#lengths
use super::{AllowQuirks, Number, Percentage, ToComputedValue};
use crate::font_metrics::FontMetrics;
use crate::font_metrics::{FontMetrics, FontMetricsOrientation};
use crate::parser::{Parse, ParserContext};
use crate::properties::computed_value_flags::ComputedValueFlags;
use crate::values::computed::{self, CSSPixelLength, Context};
@ -133,8 +133,9 @@ impl FontRelativeLength {
fn query_font_metrics(
context: &Context,
base_size: FontBaseSize,
orientation: FontMetricsOrientation,
) -> FontMetrics {
context.font_metrics_provider.query(context, base_size)
context.font_metrics_provider.query(context, base_size, orientation)
}
let reference_font_size = base_size.resolve(context);
@ -160,7 +161,12 @@ impl FontRelativeLength {
context.rule_cache_conditions.borrow_mut().set_uncacheable();
}
context.builder.add_flags(ComputedValueFlags::DEPENDS_ON_FONT_METRICS);
let metrics = query_font_metrics(context, base_size);
// The x-height is an intrinsically horizontal metric.
let metrics = query_font_metrics(
context,
base_size,
FontMetricsOrientation::Horizontal
);
let reference_size = metrics.x_height.unwrap_or_else(|| {
// https://drafts.csswg.org/css-values/#ex
//
@ -177,7 +183,18 @@ impl FontRelativeLength {
context.rule_cache_conditions.borrow_mut().set_uncacheable();
}
context.builder.add_flags(ComputedValueFlags::DEPENDS_ON_FONT_METRICS);
let metrics = query_font_metrics(context, base_size);
// https://drafts.csswg.org/css-values/#ch:
//
// Equal to the used advance measure of the “0” (ZERO,
// U+0030) glyph in the font used to render it. (The advance
// measure of a glyph is its advance width or height,
// whichever is in the inline axis of the element.)
//
let metrics = query_font_metrics(
context,
base_size,
FontMetricsOrientation::MatchContext,
);
let reference_size = metrics.zero_advance_measure.unwrap_or_else(|| {
// https://drafts.csswg.org/css-values/#ch
//
@ -189,7 +206,8 @@ impl FontRelativeLength {
// writing-mode is vertical-rl or vertical-lr and
// text-orientation is upright).
//
if context.style().writing_mode.is_vertical() {
let wm = context.style().writing_mode;
if wm.is_vertical() && wm.is_upright() {
reference_font_size
} else {
reference_font_size.scale_by(0.5)