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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
//! Access to font metrics from the style system.
#![deny(missing_docs)]
use crate::values::computed::Length;
/// 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: Option<Length>,
/// The zero advance. This is usually writing mode dependent
pub zero_advance_measure: Option<Length>,
/// The cap-height of the font.
pub cap_height: Option<Length>,
/// The ideographic-width of the font.
pub ic_width: Option<Length>,
/// The ascent of the font (a value is always available for this).
pub ascent: Length,
/// Script scale down factor for math-depth 1.
pub script_percent_scale_down: Option<f32>,
/// Script scale down factor for math-depth 2.
pub script_script_percent_scale_down: Option<f32>,
}
impl Default for FontMetrics {
fn default() -> Self {
FontMetrics {
x_height: None,
zero_advance_measure: None,
cap_height: None,
ic_width: None,
ascent: Length::new(0.0),
script_percent_scale_down: None,
script_script_percent_scale_down: None,
}
}
}
impl FontMetrics {
/// Returns the x-height, computing a fallback value if not present
pub fn x_height_or_default(&self, reference_font_size: Length) -> Length {
//
// In the cases where it is impossible or impractical to
// determine the x-height, a value of 0.5em must be
// assumed.
//
// (But note we use 0.5em of the used, not computed
// font-size)
self.x_height.unwrap_or_else(|| reference_font_size * 0.5)
}
/// Returns the zero advance measure, computing a fallback value if not present
pub fn zero_advance_measure_or_default(
&self,
reference_font_size: Length,
upright: bool,
) -> Length {
//
// In the cases where it is impossible or impractical to
// determine the measure of the “0” glyph, it must be
// assumed to be 0.5em wide by 1em tall. Thus, the ch
// unit falls back to 0.5em in the general case, and to
// 1em when it would be typeset upright (i.e.
// writing-mode is vertical-rl or vertical-lr and
// text-orientation is upright).
//
// Same caveat about computed vs. used font-size applies
// above.
self.zero_advance_measure.unwrap_or_else(|| {
if upright {
reference_font_size
} else {
reference_font_size * 0.5
}
})
}
/// Returns the cap-height, computing a fallback value if not present
pub fn cap_height_or_default(&self) -> Length {
//
// In the cases where it is impossible or impractical to
// determine the cap-height, the font’s ascent must be
// used.
//
self.cap_height.unwrap_or_else(|| self.ascent)
}
/// Returns the ideographic advance measure, computing a fallback value if not present
pub fn ic_width_or_default(&self, reference_font_size: Length) -> Length {
//
// In the cases where it is impossible or impractical to
// determine the ideographic advance measure, it must be
// assumed to be 1em.
//
// Same caveat about computed vs. used as for other
// metric-dependent units.
self.ic_width.unwrap_or_else(|| reference_font_size)
}
}
/// Type of font metrics to retrieve.
#[derive(Clone, Debug, PartialEq)]
pub enum FontMetricsOrientation {
/// Get metrics for horizontal or vertical according to the Context's
/// writing mode, using horizontal metrics for vertical/mixed
MatchContextPreferHorizontal,
/// Get metrics for horizontal or vertical according to the Context's
/// writing mode, using vertical metrics for vertical/mixed
MatchContextPreferVertical,
/// Force getting horizontal metrics.
Horizontal,
}