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// font-kit/src/matching.rs
//
// Copyright © 2018 The Pathfinder Project Developers.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Determines the closest font matching a description per the CSS Fonts Level 3 specification.
use float_ord::FloatOrd;
use error::SelectionError;
use properties::{Properties, Stretch, Style, Weight};
pub struct Description {
pub family_name: String,
pub properties: Properties,
}
/// This follows CSS Fonts Level 3 § 5.2 [1].
///
/// https://drafts.csswg.org/css-fonts-3/#font-style-matching
pub fn find_best_match(candidates: &[Description], query: &Properties)
-> Result<usize, SelectionError> {
// Step 4.
let mut matching_set: Vec<usize> = (0..candidates.len()).collect();
if matching_set.is_empty() {
return Err(SelectionError::NotFound)
}
// Step 4a (`font-stretch`).
let matching_stretch =
if matching_set.iter().any(|&index| {
candidates[index].properties.stretch == query.stretch
}) {
// Exact match.
query.stretch
} else if query.stretch <= Stretch::NORMAL {
// Closest width, first checking narrower values and then wider values.
match matching_set.iter()
.filter(|&&index| {
candidates[index].properties.stretch < query.stretch
})
.min_by_key(|&&index| {
FloatOrd(query.stretch.0 - candidates[index].properties.stretch.0)
}) {
Some(&matching_index) => candidates[matching_index].properties.stretch,
None => {
let matching_index =
*matching_set.iter()
.min_by_key(|&&index| {
FloatOrd(candidates[index].properties.stretch.0 -
query.stretch.0)
})
.unwrap();
candidates[matching_index].properties.stretch
}
}
} else {
// Closest width, first checking wider values and then narrower values.
match matching_set.iter()
.filter(|&&index| {
candidates[index].properties.stretch > query.stretch
})
.min_by_key(|&&index| {
FloatOrd(candidates[index].properties.stretch.0 - query.stretch.0)
}) {
Some(&matching_index) => candidates[matching_index].properties.stretch,
None => {
let matching_index =
*matching_set.iter()
.min_by_key(|&&index| {
FloatOrd(query.stretch.0 -
candidates[index].properties.stretch.0)
})
.unwrap();
candidates[matching_index].properties.stretch
}
}
};
matching_set.retain(|&index| candidates[index].properties.stretch == matching_stretch);
// Step 4b (`font-style`).
let style_preference = match query.style {
Style::Italic => [Style::Italic, Style::Oblique, Style::Normal],
Style::Oblique => [Style::Oblique, Style::Italic, Style::Normal],
Style::Normal => [Style::Normal, Style::Oblique, Style::Italic],
};
let matching_style = *style_preference.iter().filter(|&query_style| {
matching_set.iter().any(|&index| candidates[index].properties.style == *query_style)
}).next().unwrap();
matching_set.retain(|&index| candidates[index].properties.style == matching_style);
// Step 4c (`font-weight`).
//
// The spec doesn't say what to do if the weight is between 400 and 500 exclusive, so we
// just use 450 as the cutoff.
let matching_weight =
if query.weight >= Weight(400.0) && query.weight < Weight(450.0) &&
matching_set.iter()
.any(|&index| candidates[index].properties.weight == Weight(500.0)) {
// Check 500 first.
Weight(500.0)
} else if query.weight >= Weight(450.0) && query.weight <= Weight(500.0) &&
matching_set.iter()
.any(|&index| candidates[index].properties.weight == Weight(400.0)) {
// Check 400 first.
Weight(400.0)
} else if query.weight <= Weight(500.0) {
// Closest weight, first checking thinner values and then fatter ones.
match matching_set.iter()
.filter(|&&index| {
candidates[index].properties.weight <= query.weight
})
.min_by_key(|&&index| {
FloatOrd(query.weight.0 - candidates[index].properties.weight.0)
}) {
Some(&matching_index) => candidates[matching_index].properties.weight,
None => {
let matching_index =
*matching_set.iter()
.min_by_key(|&&index| {
FloatOrd(candidates[index].properties.weight.0 -
query.weight.0)
})
.unwrap();
candidates[matching_index].properties.weight
}
}
} else {
// Closest weight, first checking fatter values and then thinner ones.
match matching_set.iter()
.filter(|&&index| {
candidates[index].properties.weight >= query.weight
})
.min_by_key(|&&index| {
FloatOrd(candidates[index].properties.weight.0 - query.weight.0)
}) {
Some(&matching_index) => candidates[matching_index].properties.weight,
None => {
let matching_index =
*matching_set.iter()
.min_by_key(|&&index| {
FloatOrd(query.weight.0 -
candidates[index].properties.weight.0)
})
.unwrap();
candidates[matching_index].properties.weight
}
}
};
matching_set.retain(|&index| candidates[index].properties.weight == matching_weight);
// Step 4d concerns `font-size`, but fonts in `font-kit` are unsized, so we ignore that.
// Return the result.
matching_set.into_iter().next().ok_or(SelectionError::NotFound)
}