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633a064655
r=heycam https://bugzilla.mozilla.org/show_bug.cgi?id=1341724 Source-Repo: https://github.com/servo/servo Source-Revision: dafa6c94eb3c748d6aa81f460e262882741cf7bd --HG-- extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear extra : subtree_revision : 421534b0e9f8691861a96baee131c2e8206b2693
91 lines
3.2 KiB
Rust
91 lines
3.2 KiB
Rust
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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//! Access to font metrics from the style system.
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#![deny(missing_docs)]
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use Atom;
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use app_units::Au;
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use context::SharedStyleContext;
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use logical_geometry::WritingMode;
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use media_queries::Device;
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use properties::style_structs::Font;
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use std::fmt;
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/// Represents the font metrics that style needs from a font to compute the
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/// value of certain CSS units like `ex`.
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#[derive(Debug, PartialEq, Clone)]
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pub struct FontMetrics {
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/// The x-height of the font.
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pub x_height: Au,
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/// The zero advance. This is usually writing mode dependent
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pub zero_advance_measure: Au,
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}
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/// The result for querying font metrics for a given font family.
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#[derive(Debug, PartialEq, Clone)]
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pub enum FontMetricsQueryResult {
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/// The font is available, but we may or may not have found any font metrics
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/// for it.
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Available(FontMetrics),
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/// The font is not available.
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NotAvailable,
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}
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/// A trait used to represent something capable of providing us font metrics.
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pub trait FontMetricsProvider: fmt::Debug {
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/// Obtain the metrics for given font family.
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///
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/// TODO: We could make this take the full list, I guess, and save a few
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/// virtual calls in the case we are repeatedly unable to find font metrics?
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/// That is not too common in practice though.
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fn query(&self, _font: &Font, _font_size: Au, _wm: WritingMode,
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_in_media_query: bool, _device: &Device) -> FontMetricsQueryResult {
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FontMetricsQueryResult::NotAvailable
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}
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/// Get default size of a given language and generic family
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fn get_size(&self, font_name: &Atom, font_family: u8) -> Au;
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/// Construct from a shared style context
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fn create_from(context: &SharedStyleContext) -> Self where Self: Sized;
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}
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// TODO: Servo's font metrics provider will probably not live in this crate, so this will
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// have to be replaced with something else (perhaps a trait method on TElement)
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// when we get there
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#[derive(Debug)]
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#[cfg(feature = "servo")]
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/// Dummy metrics provider for Servo. Knows nothing about fonts and does not provide
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/// any metrics.
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pub struct ServoMetricsProvider;
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#[cfg(feature = "servo")]
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impl FontMetricsProvider for ServoMetricsProvider {
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fn create_from(_: &SharedStyleContext) -> Self {
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ServoMetricsProvider
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}
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fn get_size(&self, _font_name: &Atom, _font_family: u8) -> Au {
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unreachable!("Dummy provider should never be used to compute font size")
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}
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}
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// Servo's font metrics provider will probably not live in this crate, so this will
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// have to be replaced with something else (perhaps a trait method on TElement)
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// when we get there
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#[cfg(feature = "gecko")]
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/// Construct a font metrics provider for the current product
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pub fn get_metrics_provider_for_product() -> ::gecko::wrapper::GeckoFontMetricsProvider {
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::gecko::wrapper::GeckoFontMetricsProvider::new()
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}
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#[cfg(feature = "servo")]
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/// Construct a font metrics provider for the current product
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pub fn get_metrics_provider_for_product() -> ServoMetricsProvider {
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ServoMetricsProvider
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}
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