max / shop

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1	//! Asking the system which font has a character the bundled one does not.
2	//!
3	//! Shop bundles one font so that a fresh install has its box drawing and its
4	//! house marks without a font install first, and that font is Quasi Mono:
5	//! Latin, Greek, Cyrillic, box drawing and block elements in full, and no Han,
6	//! kana or hangul at all.
7	//!
8	//! Rather than pick a second font ourselves and ship it, ask the machine. On
9	//! Linux fontconfig is the thing that already knows, and already carries the
10	//! user's own preferences and per-language rules, so a system that has been
11	//! told to prefer a particular CJK face gets that face here too. Shop is
12	//! Wayland-only, so fontconfig is present wherever shop runs, and it is
13	//! consulted only when the bundled font misses, which for ordinary output is
14	//! never.
15	//!
16	//! What this path is for is scripts, and it is a poor answer for symbols.
17	//! `Shaper::baseline` takes the line off the primary face alone, deliberately,
18	//! so a fallback face with its own metrics sits its glyphs on a different line.
19	//! For a run of Han that is right; for a box-drawing character it would draw
20	//! borders off the line, which is why the whole cell tier is in the face rather
21	//! than left to fallback. Two blocks are outside it and now arrive this way:
22	//! braille (U+2800) and the legacy-computing sextants, which IosevkaTerm
23	//! carried and Quasi Mono does not. Nothing in the tree emits either - there is
24	//! no `Canvas` and no `Sparkline` anywhere - and the day one does, they are
25	//! generated recipes in the house set rather than a fallback.
26
27	use fontconfig::{CharSet, Fontconfig, Pattern};
28
29	/// A font file the system offered, and which face inside it.
30	pub(crate) struct Match {
31	pub(crate) path: String,
32	pub(crate) index: i32,
33	}
34
35	pub(crate) struct Fallback {
36	/// `None` when fontconfig could not initialise. Every lookup then misses,
37	/// which is the behaviour shop had before this existed: tofu, not a crash.
38	fc: Option<Fontconfig>,
39	}
40
41	impl Fallback {
42	pub(crate) fn new() -> Self {
43	let fc = Fontconfig::new();
44	if fc.is_none() {
45	tracing::warn!("fontconfig unavailable; characters outside the bundled font draw tofu");
46	}
47	Self { fc }
48	}
49
50	/// The font the system would use for `c`, or `None` if nothing has it.
51	///
52	/// Asks by CHARACTER rather than by family: a charset of one is what makes
53	/// this "who has this glyph" instead of "give me a font I named", which is
54	/// the whole point of deferring to the system.
55	pub(crate) fn find(&self, c: char) -> Option<Match> {
56	let fc = self.fc.as_ref()?;
57	let mut charset = CharSet::new(fc).ok()?;
58	charset.add_char(c).ok()?;
59
60	let mut pat = Pattern::new(fc).ok()?;
61	pat.add_charset(charset).ok()?;
62	// Rank monospace faces first. Not a filter — fontconfig always returns
63	// its best match — but it is the difference between "Noto Sans CJK JP"
64	// and "Noto Sans Mono CJK JP", and only the second one is built to sit
65	// in a grid of cells.
66	pat.add_integer(c"spacing", 100).ok()?;
67	// The user's fontconfig rules, then the built-in defaults. Skipping
68	// these would be asking the library while ignoring its configuration,
69	// which is most of what makes the answer the system's rather than ours.
70	pat.config_substitute().ok()?;
71	pat.default_substitute();
72
73	let found = pat.font_match().ok()?;
74	Some(Match {
75	path: found.filename().ok()?.to_string(),
76	index: found.face_index().unwrap_or(0),
77	})
78	}
79	}
80