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/* 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 https://mozilla.org/MPL/2.0/. */
//! Access to font metrics from the style system.
#![deny(missing_docs)]
use app_units::Au;
use crate::context::SharedStyleContext;
use crate::logical_geometry::WritingMode;
use crate::media_queries::Device;
use crate::properties::style_structs::Font;
use crate::Atom;
/// Represents the font metrics that style needs from a font to compute the
/// value of certain CSS units like `ex`.
#[derive(Clone, Debug, PartialEq)]
pub struct FontMetrics {
/// The x-height of the font.
pub x_height: Au,
/// The zero advance. This is usually writing mode dependent
pub zero_advance_measure: Au,
}
/// The result for querying font metrics for a given font family.
#[derive(Clone, Debug, PartialEq)]
pub enum FontMetricsQueryResult {
/// The font is available, but we may or may not have found any font metrics
/// for it.
Available(FontMetrics),
/// The font is not available.
NotAvailable,
}
/// A trait used to represent something capable of providing us font metrics.
pub trait FontMetricsProvider {
/// Obtain the metrics for given font family.
///
/// TODO: We could make this take the full list, I guess, and save a few
/// virtual calls in the case we are repeatedly unable to find font metrics?
/// That is not too common in practice though.
fn query(
&self,
_font: &Font,
_font_size: Au,
_wm: WritingMode,
_in_media_query: bool,
_device: &Device,
) -> FontMetricsQueryResult {
FontMetricsQueryResult::NotAvailable
}
/// Get default size of a given language and generic family
fn get_size(&self, font_name: &Atom, font_family: u8) -> Au;
/// Construct from a shared style context
fn create_from(context: &SharedStyleContext) -> Self
where
Self: Sized;
}
// TODO: Servo's font metrics provider will probably not live in this crate, so this will
// have to be replaced with something else (perhaps a trait method on TElement)
// when we get there
#[derive(Debug)]
#[cfg(feature = "servo")]
/// Dummy metrics provider for Servo. Knows nothing about fonts and does not provide
/// any metrics.
pub struct ServoMetricsProvider;
#[cfg(feature = "servo")]
impl FontMetricsProvider for ServoMetricsProvider {
fn create_from(_: &SharedStyleContext) -> Self {
ServoMetricsProvider
}
fn get_size(&self, _font_name: &Atom, _font_family: u8) -> Au {
unreachable!("Dummy provider should never be used to compute font size")
}
}
// Servo's font metrics provider will probably not live in this crate, so this will
// have to be replaced with something else (perhaps a trait method on TElement)
// when we get there
#[cfg(feature = "gecko")]
/// Construct a font metrics provider for the current product
pub fn get_metrics_provider_for_product() -> crate::gecko::wrapper::GeckoFontMetricsProvider {
crate::gecko::wrapper::GeckoFontMetricsProvider::new()
}
#[cfg(feature = "servo")]
/// Construct a font metrics provider for the current product
pub fn get_metrics_provider_for_product() -> ServoMetricsProvider {
ServoMetricsProvider
}
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