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style: Allow FontMetricsProvider to produce ex height and zero width independently.

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We are always able to produce an x height, but depending on whether the
glyph exists, we sometimes can't produce a zero glyph width.

Differential Revision: https://phabricator.services.mozilla.com/D23424
This commit is contained in:
Cameron McCormack 2019-03-21 04:50:43 +00:00 • committed by Emilio Cobos Álvarez
parent 39df092bce
commit d5f208e18c
3 changed files with 29 additions and 38 deletions
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30
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::FontMetricsQueryResult;
use crate::font_metrics::FontMetrics;
use crate::parser::{Parse, ParserContext};
use crate::properties::computed_value_flags::ComputedValueFlags;
use crate::values::computed::{self, CSSPixelLength, Context};
@ -133,7 +133,7 @@ impl FontRelativeLength {
fn query_font_metrics(
context: &Context,
base_size: FontBaseSize,
) -> FontMetricsQueryResult {
) -> FontMetrics {
context.font_metrics_provider.query(context, base_size)
}
@ -160,16 +160,16 @@ impl FontRelativeLength {
context.rule_cache_conditions.borrow_mut().set_uncacheable();
}
context.builder.add_flags(ComputedValueFlags::DEPENDS_ON_FONT_METRICS);
let reference_size = match query_font_metrics(context, base_size) {
FontMetricsQueryResult::Available(metrics) => metrics.x_height,
let metrics = query_font_metrics(context, base_size);
let reference_size = metrics.x_height.unwrap_or_else(|| {
// https://drafts.csswg.org/css-values/#ex
//
// In the cases where it is impossible or impractical to
// determine the x-height, a value of 0.5em must be
// assumed.
//
FontMetricsQueryResult::NotAvailable => reference_font_size.scale_by(0.5),
};
reference_font_size.scale_by(0.5)
});
(reference_size, length)
},
FontRelativeLength::Ch(length) => {
@ -177,8 +177,8 @@ impl FontRelativeLength {
context.rule_cache_conditions.borrow_mut().set_uncacheable();
}
context.builder.add_flags(ComputedValueFlags::DEPENDS_ON_FONT_METRICS);
let reference_size = match query_font_metrics(context, base_size) {
FontMetricsQueryResult::Available(metrics) => metrics.zero_advance_measure,
let metrics = query_font_metrics(context, base_size);
let reference_size = metrics.zero_advance_measure.unwrap_or_else(|| {
// https://drafts.csswg.org/css-values/#ch
//
// In the cases where it is impossible or impractical to
@ -189,14 +189,12 @@ impl FontRelativeLength {
// writing-mode is vertical-rl or vertical-lr and
// text-orientation is upright).
//
FontMetricsQueryResult::NotAvailable => {
if context.style().writing_mode.is_vertical() {
reference_font_size
} else {
reference_font_size.scale_by(0.5)
}
},
};
if context.style().writing_mode.is_vertical() {
reference_font_size
} else {
reference_font_size.scale_by(0.5)
}
});
(reference_size, length)
},
FontRelativeLength::Rem(length) => {