gpui_core/

text_system.rs

mod font_fallbacks;
mod font_features;
mod line;
mod line_layout;
mod line_wrapper;

pub use font_fallbacks::*;
pub use font_features::*;
pub use line::*;
pub use line_layout::*;
pub use line_wrapper::*;
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};

use crate::{
    Bounds, DevicePixels, Hsla, Pixels, PlatformTextSystem, Point, Result, SharedString, Size,
    StrikethroughStyle, UnderlineStyle, px,
};
use anyhow::{Context as _, anyhow};
use collections::{FxHashMap, FxHashSet};
use core::fmt;
use derive_more::{Add, Deref, FromStr, Sub};
use itertools::Itertools;
use parking_lot::{Mutex, RwLock, RwLockUpgradableReadGuard};
use smallvec::{SmallVec, smallvec};
use std::{
    borrow::Cow,
    cmp,
    collections::VecDeque,
    fmt::{Debug, Display, Formatter},
    hash::{Hash, Hasher},
    ops::{Deref, DerefMut, Range},
    sync::{
        Arc,
        atomic::{AtomicUsize, Ordering},
    },
};

/// An opaque identifier for a specific font.
#[derive(Hash, PartialEq, Eq, Clone, Copy, Debug)]
#[repr(C)]
pub struct FontId(pub usize);

/// An opaque identifier for a specific font family.
#[derive(Hash, PartialEq, Eq, Clone, Copy, Debug)]
pub struct FontFamilyId(pub usize);

/// Number of subpixel glyph variants along the X axis.
pub const SUBPIXEL_VARIANTS_X: u8 = 4;

/// Number of subpixel glyph variants along the Y axis.
pub const SUBPIXEL_VARIANTS_Y: u8 = 1;

const MAX_REPORTED_MISSING_GLYPHS: usize = 1024;

/// The spacing behavior required of a fallback font.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum FallbackFontClass {
    /// A proportionally spaced fallback font.
    Proportional,
    /// A fixed-width fallback font.
    Monospace,
}

/// A grapheme cluster that could not be represented by any available font.
#[derive(Clone, Debug, Eq, Hash, PartialEq)]
pub struct MissingGlyph {
    grapheme: SharedString,
    font_class: FallbackFontClass,
}

impl MissingGlyph {
    /// Creates a missing-glyph report.
    pub fn new(grapheme: SharedString, font_class: FallbackFontClass) -> Self {
        Self {
            grapheme,
            font_class,
        }
    }

    /// Returns the unresolved grapheme cluster.
    pub fn grapheme(&self) -> &str {
        &self.grapheme
    }

    /// Returns the spacing behavior required of a fallback font.
    pub fn font_class(&self) -> FallbackFontClass {
        self.font_class
    }
}

/// Accepts missing glyphs detected by a platform text system.
pub trait MissingGlyphSink: Send + Sync {
    /// Reports grapheme clusters that exhausted font fallback.
    fn report(&self, missing_glyphs: Vec<MissingGlyph>);
}

#[derive(Default)]
struct MissingGlyphState {
    reported: FxHashSet<MissingGlyph>,
    reported_order: VecDeque<MissingGlyph>,
    generation: usize,
}

impl MissingGlyphState {
    fn reset(&mut self, generation: usize) {
        self.reported.clear();
        self.reported_order.clear();
        self.generation = generation;
    }
}

// Read by `MissingGlyphReceiver::recv`, which runs after an application
// subscribes via `App::on_missing_glyphs`.
struct QueuedMissingGlyph {
    generation: usize,
    missing_glyph: MissingGlyph,
}

/// Collects missing-glyph reports without invoking application code during layout.
struct MissingGlyphReporter {
    generation: Arc<AtomicUsize>,
    sender: async_channel::Sender<QueuedMissingGlyph>,
}

impl MissingGlyphSink for MissingGlyphReporter {
    fn report(&self, missing_glyphs: Vec<MissingGlyph>) {
        if self.sender.is_closed() {
            return;
        }

        let generation = self.generation.load(Ordering::Acquire);
        // Repetitions within a line must not fill the queue before its other
        // missing glyphs. Cross-report deduplication belongs to the receiver.
        for missing_glyph in missing_glyphs.into_iter().unique() {
            let queued = QueuedMissingGlyph {
                generation,
                missing_glyph,
            };
            if self.sender.try_send(queued).is_err() {
                break;
            }
        }
    }
}

impl MissingGlyphReporter {
    fn reset(&self) {
        self.generation.fetch_add(1, Ordering::AcqRel);
    }
}

/// Receives batches of grapheme clusters that exhausted font fallback.
pub(crate) struct MissingGlyphReceiver {
    state: MissingGlyphState,
    generation: Arc<AtomicUsize>,
    receiver: async_channel::Receiver<QueuedMissingGlyph>,
}

impl MissingGlyphReceiver {
    /// Waits until at least one new missing glyph has been observed.
    ///
    /// # Errors
    ///
    /// Returns [`async_channel::RecvError`] if the reporting channel is closed.
    pub(crate) async fn recv(
        &mut self,
    ) -> std::result::Result<Vec<MissingGlyph>, async_channel::RecvError> {
        loop {
            let queued = self.receiver.recv().await?;
            let mut missing_glyphs = Vec::new();
            for queued in std::iter::once(queued)
                .chain(std::iter::from_fn(|| self.receiver.try_recv().ok()))
                .take(MAX_REPORTED_MISSING_GLYPHS)
            {
                let generation = self.generation.load(Ordering::Acquire);
                if self.state.generation != generation {
                    self.state.reset(generation);
                    missing_glyphs.clear();
                }
                if queued.generation != generation
                    || !self.state.reported.insert(queued.missing_glyph.clone())
                {
                    continue;
                }
                self.state
                    .reported_order
                    .push_back(queued.missing_glyph.clone());
                missing_glyphs.push(queued.missing_glyph);
                if self.state.reported.len() > MAX_REPORTED_MISSING_GLYPHS
                    && let Some(expired) = self.state.reported_order.pop_front()
                {
                    self.state.reported.remove(&expired);
                }
            }
            if !missing_glyphs.is_empty() {
                return Ok(missing_glyphs);
            }
            // A producer can keep refilling the queue with already-reported
            // glyphs. Bound work per poll even when every report is filtered out.
            let mut yielded = false;
            std::future::poll_fn(|cx| {
                if std::mem::replace(&mut yielded, true) {
                    std::task::Poll::Ready(())
                } else {
                    cx.waker().wake_by_ref();
                    std::task::Poll::Pending
                }
            })
            .await;
        }
    }
}

impl Drop for MissingGlyphReceiver {
    fn drop(&mut self) {
        self.receiver.close();
        while self.receiver.try_recv().is_ok() {}
    }
}

/// Snapshot of the long-lived text-system cache sizes returned by
/// [`TextSystem::layout_cache_stats`].
///
/// All fields are entry counts (not bytes). Use these together with the
/// configured caps in [`crate::TextResourceBudget`] to understand how
/// saturated the caches are before deciding to call
/// [`TextSystem::clear_layout_cache`].
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct TextSystemCacheStats {
    /// Number of shaped, unwrapped line layouts in the global cache.
    pub lines: usize,
    /// Number of shaped, wrapped line layouts in the global cache.
    pub wrapped_lines: usize,
    /// Number of glyph raster-bounds entries.
    pub raster_bounds: usize,
}

/// The GPUI text rendering sub system.
pub struct TextSystem {
    platform_text_system: Arc<dyn PlatformTextSystem>,
    global_line_layout_cache: Arc<GlobalLineLayoutCache>,
    font_ids_by_font: RwLock<FxHashMap<Font, Result<FontId>>>,
    font_metrics: RwLock<FxHashMap<FontId, FontMetrics>>,
    raster_bounds: RwLock<FxHashMap<RenderGlyphParams, Bounds<DevicePixels>>>,
    raster_bounds_max_entries: Option<usize>,
    wrapper_pool: Mutex<FxHashMap<FontIdWithSize, Vec<LineWrapper>>>,
    font_runs_pool: Mutex<Vec<Vec<FontRun>>>,
    fallback_font_stack: SmallVec<[Font; 2]>,
    font_generation: Arc<AtomicUsize>,
    missing_glyph_reporter: Arc<MissingGlyphReporter>,
    // Held so the reporting channel stays open. Taken when a callback is registered.
    missing_glyph_receiver: Mutex<Option<MissingGlyphReceiver>>,
}

impl TextSystem {
    pub(crate) fn new(
        platform_text_system: Arc<dyn PlatformTextSystem>,
        text_budget: &crate::TextResourceBudget,
    ) -> Self {
        let (sender, receiver) = async_channel::bounded(MAX_REPORTED_MISSING_GLYPHS);
        let missing_glyph_generation = Arc::<AtomicUsize>::default();
        let missing_glyph_reporter = Arc::new(MissingGlyphReporter {
            generation: missing_glyph_generation.clone(),
            sender,
        });
        // Platforms that detect exhausted font fallback report through this sink.
        platform_text_system.set_missing_glyph_sink(missing_glyph_reporter.clone());
        TextSystem {
            platform_text_system,
            global_line_layout_cache: Arc::new(GlobalLineLayoutCache::new(
                text_budget.line_layout_cache_max_entries,
                text_budget.line_layout_cache_low_watermark,
            )),
            font_metrics: RwLock::default(),
            raster_bounds: RwLock::default(),
            raster_bounds_max_entries: text_budget.raster_bounds_cache_max_entries,
            font_ids_by_font: RwLock::default(),
            wrapper_pool: Mutex::default(),
            font_runs_pool: Mutex::default(),
            fallback_font_stack: smallvec![
                // TODO: Remove this when Linux have implemented setting fallbacks.
                font(".ZedMono"),
                font(".ZedSans"),
                font("Helvetica"),
                font("Segoe UI"),  // Windows
                font("Cantarell"), // Gnome
                font("Ubuntu"),    // Gnome (Ubuntu)
                font("Noto Sans"), // KDE
                font("DejaVu Sans")
            ],
            font_generation: Arc::default(),
            missing_glyph_reporter,
            missing_glyph_receiver: Mutex::new(Some(MissingGlyphReceiver {
                state: MissingGlyphState::default(),
                generation: missing_glyph_generation,
                receiver,
            })),
        }
    }

    #[cfg(test)]
    pub(crate) fn resource_budget_for_test(&self) -> (usize, usize, Option<usize>) {
        let (max_entries, low_watermark) = self.global_line_layout_cache.budget_for_test();
        (max_entries, low_watermark, self.raster_bounds_max_entries)
    }

    /// Drop every entry held by the long-lived text caches.
    ///
    /// This releases the global line-layout cache (shaped lines and wrapped
    /// lines) and the glyph raster-bounds cache. The caches will repopulate
    /// naturally as text is laid out again, at the cost of a one-time shaping
    /// pass on the next render.
    ///
    /// Intended for use by long-running applications that experience an idle
    /// or hidden state (e.g. tray apps when the popup closes) and want to
    /// reclaim heap memory. Per-frame caches owned by [`WindowTextSystem`] are
    /// not affected — they are cleared on every frame already and dropped
    /// with the window.
    pub fn clear_layout_cache(&self) {
        self.global_line_layout_cache.clear();
        self.raster_bounds.write().clear();
        self.platform_text_system.clear_glyph_raster_cache();
    }

    /// Snapshot of the current sizes of the long-lived text caches, primarily
    /// for diagnostics and benchmarking. Counts are entry counts, not bytes.
    pub fn layout_cache_stats(&self) -> TextSystemCacheStats {
        let (lines, wrapped_lines) = self.global_line_layout_cache.entry_counts();
        TextSystemCacheStats {
            lines,
            wrapped_lines,
            raster_bounds: self.raster_bounds.read().len(),
        }
    }

    /// Get sorted, unique font family names available to the platform text system.
    ///
    /// Includes fonts registered with [`Self::add_fonts`].
    pub fn all_font_names(&self) -> Vec<String> {
        let mut names = self.platform_text_system.all_font_names();
        names.sort_unstable();
        names.dedup();
        names
    }

    /// Add a font's data to the text system.
    ///
    /// Cached font resolution and line layouts are invalidated after installation.
    /// Layouts already in progress may complete against the previous font set.
    pub fn add_fonts(&self, fonts: Vec<Cow<'static, [u8]>>) -> Result<()> {
        self.platform_text_system.add_fonts(fonts)?;
        self.font_ids_by_font.write().clear();
        self.missing_glyph_reporter.reset();
        self.font_generation.fetch_add(1, Ordering::Release);
        Ok(())
    }

    /// Takes the receiver for missing-glyph reports.
    ///
    /// Only one receiver is available for each text system. Returns `None` when
    /// the receiver was already taken or another caller is taking it.
    pub(crate) fn take_missing_glyph_receiver(&self) -> Option<MissingGlyphReceiver> {
        self.missing_glyph_receiver
            .try_lock()
            .and_then(|mut receiver| receiver.take())
    }

    #[cfg(test)]
    pub(crate) fn report_missing_glyphs_in_test(&self, missing_glyphs: Vec<MissingGlyph>) {
        self.missing_glyph_reporter.report(missing_glyphs);
    }

    /// Prewarm any system font caches needed to shape text.
    ///
    /// This may be expensive, so callers should generally invoke it on a
    /// background executor. Missing entries are still populated on demand by
    /// the normal shaping path.
    pub fn prewarm_fonts(&self, fonts: &[Font]) {
        let mut font_ids = SmallVec::<[FontId; 8]>::new();
        for font in fonts {
            let font_id = self.resolve_font(font);
            if !font_ids.contains(&font_id) {
                font_ids.push(font_id);
            }
        }
        self.platform_text_system.prewarm_fonts(&font_ids);
    }

    /// Returns the platform-recommended glyph dilation level for the given foreground color.
    /// Used to compensate perceived stroke weight on platforms where the OS text renderer
    /// applies font-smoothing differently for light vs dark glyphs.
    pub fn glyph_dilation_for_color(&self, color: Hsla) -> u8 {
        self.platform_text_system.glyph_dilation_for_color(color)
    }

    /// Get the FontId for the configure font family and style.
    fn font_id(&self, font: &Font) -> Result<FontId> {
        fn clone_font_id_result(font_id: &Result<FontId>) -> Result<FontId> {
            match font_id {
                Ok(font_id) => Ok(*font_id),
                Err(err) => Err(anyhow!("{err}")),
            }
        }

        let font_id = self
            .font_ids_by_font
            .read()
            .get(font)
            .map(clone_font_id_result);
        if let Some(font_id) = font_id {
            font_id
        } else {
            let font_id = self.platform_text_system.font_id(font);
            self.font_ids_by_font
                .write()
                .insert(font.clone(), clone_font_id_result(&font_id));
            font_id
        }
    }

    /// Get the Font for the Font Id.
    pub fn get_font_for_id(&self, id: FontId) -> Option<Font> {
        let lock = self.font_ids_by_font.read();
        lock.iter()
            .filter_map(|(font, result)| match result {
                Ok(font_id) if *font_id == id => Some(font.clone()),
                _ => None,
            })
            .next()
    }

    /// Resolves the specified font, falling back to the default font stack if
    /// the font fails to load.
    ///
    /// # Panics
    ///
    /// Panics if the font and none of the fallbacks can be resolved.
    pub fn resolve_font(&self, font: &Font) -> FontId {
        if let Ok(font_id) = self.font_id(font) {
            return font_id;
        }
        for fallback in &self.fallback_font_stack {
            if let Ok(font_id) = self.font_id(fallback) {
                return font_id;
            }
        }

        panic!(
            "failed to resolve font '{}' or any of the fallbacks: {}",
            font.family,
            self.fallback_font_stack
                .iter()
                .map(|fallback| &fallback.family)
                .join(", ")
        );
    }

    /// Get the bounding box for the given font and font size.
    /// A font's bounding box is the smallest rectangle that could enclose all glyphs
    /// in the font. superimposed over one another.
    pub fn bounding_box(&self, font_id: FontId, font_size: Pixels) -> Bounds<Pixels> {
        self.read_metrics(font_id, |metrics| metrics.bounding_box(font_size))
    }

    /// Get the typographic bounds for the given character, in the given font and size.
    pub fn typographic_bounds(
        &self,
        font_id: FontId,
        font_size: Pixels,
        character: char,
    ) -> Result<Bounds<Pixels>> {
        let glyph_id = self
            .platform_text_system
            .glyph_for_char(font_id, character)
            .with_context(|| format!("glyph not found for character '{character}'"))?;
        let bounds = self
            .platform_text_system
            .typographic_bounds(font_id, glyph_id)?;
        Ok(self.read_metrics(font_id, |metrics| {
            (bounds / metrics.units_per_em as f32 * font_size.0).map(px)
        }))
    }

    /// Get the advance width for the given character, in the given font and size.
    pub fn advance(&self, font_id: FontId, font_size: Pixels, ch: char) -> Result<Size<Pixels>> {
        let glyph_id = self
            .platform_text_system
            .glyph_for_char(font_id, ch)
            .with_context(|| format!("glyph not found for character '{ch}'"))?;
        let result = self.platform_text_system.advance(font_id, glyph_id)?
            / self.units_per_em(font_id) as f32;

        Ok(result * font_size)
    }

    /// Returns the width of an `em`.
    ///
    /// Uses the width of the `m` character in the given font and size.
    pub fn em_width(&self, font_id: FontId, font_size: Pixels) -> Result<Pixels> {
        Ok(self.typographic_bounds(font_id, font_size, 'm')?.size.width)
    }

    /// Returns the advance width of an `em`.
    ///
    /// Uses the advance width of the `m` character in the given font and size.
    pub fn em_advance(&self, font_id: FontId, font_size: Pixels) -> Result<Pixels> {
        Ok(self.advance(font_id, font_size, 'm')?.width)
    }

    /// Returns the width of an `ch`.
    ///
    /// Uses the width of the `0` character in the given font and size.
    pub fn ch_width(&self, font_id: FontId, font_size: Pixels) -> Result<Pixels> {
        Ok(self.typographic_bounds(font_id, font_size, '0')?.size.width)
    }

    /// Returns the advance width of an `ch`.
    ///
    /// Uses the advance width of the `0` character in the given font and size.
    pub fn ch_advance(&self, font_id: FontId, font_size: Pixels) -> Result<Pixels> {
        Ok(self.advance(font_id, font_size, '0')?.width)
    }

    /// Get the number of font size units per 'em square',
    /// Per MDN: "an abstract square whose height is the intended distance between
    /// lines of type in the same type size"
    pub fn units_per_em(&self, font_id: FontId) -> u32 {
        self.read_metrics(font_id, |metrics| metrics.units_per_em)
    }

    /// Get the height of a capital letter in the given font and size.
    pub fn cap_height(&self, font_id: FontId, font_size: Pixels) -> Pixels {
        self.read_metrics(font_id, |metrics| metrics.cap_height(font_size))
    }

    /// Get the height of the x character in the given font and size.
    pub fn x_height(&self, font_id: FontId, font_size: Pixels) -> Pixels {
        self.read_metrics(font_id, |metrics| metrics.x_height(font_size))
    }

    /// Get the recommended distance from the baseline for the given font
    pub fn ascent(&self, font_id: FontId, font_size: Pixels) -> Pixels {
        self.read_metrics(font_id, |metrics| metrics.ascent(font_size))
    }

    /// Get the recommended distance below the baseline for the given font,
    /// in single spaced text.
    pub fn descent(&self, font_id: FontId, font_size: Pixels) -> Pixels {
        self.read_metrics(font_id, |metrics| metrics.descent(font_size))
    }

    /// Get the recommended baseline offset for the given font and line height.
    pub fn baseline_offset(
        &self,
        font_id: FontId,
        font_size: Pixels,
        line_height: Pixels,
    ) -> Pixels {
        let ascent = self.ascent(font_id, font_size);
        let descent = self.descent(font_id, font_size);
        let padding_top = (line_height - ascent - descent) / 2.;
        padding_top + ascent
    }

    fn read_metrics<T>(&self, font_id: FontId, read: impl FnOnce(&FontMetrics) -> T) -> T {
        let lock = self.font_metrics.upgradable_read();

        if let Some(metrics) = lock.get(&font_id) {
            read(metrics)
        } else {
            let mut lock = RwLockUpgradableReadGuard::upgrade(lock);
            let metrics = lock
                .entry(font_id)
                .or_insert_with(|| self.platform_text_system.font_metrics(font_id));
            read(metrics)
        }
    }

    /// Returns a handle to a line wrapper, for the given font and font size.
    pub fn line_wrapper(self: &Arc<Self>, font: Font, font_size: Pixels) -> LineWrapperHandle {
        let lock = &mut self.wrapper_pool.lock();
        let font_id = self.resolve_font(&font);
        let wrappers = lock
            .entry(FontIdWithSize { font_id, font_size })
            .or_default();
        let wrapper = wrappers.pop().unwrap_or_else(|| {
            LineWrapper::new(font_id, font_size, self.platform_text_system.clone())
        });

        LineWrapperHandle {
            wrapper: Some(wrapper),
            text_system: self.clone(),
        }
    }

    /// Get the rasterized size and location of a specific, rendered glyph.
    pub(crate) fn raster_bounds(&self, params: &RenderGlyphParams) -> Result<Bounds<DevicePixels>> {
        let raster_bounds = self.raster_bounds.upgradable_read();
        if let Some(bounds) = raster_bounds.get(params) {
            Ok(*bounds)
        } else {
            let mut raster_bounds = RwLockUpgradableReadGuard::upgrade(raster_bounds);
            // If a limit is set and we've exceeded it, clear the cache to
            // reclaim memory. This is a simple generational approach since
            // glyph_raster_bounds is cheap to recompute.
            if let Some(max) = self.raster_bounds_max_entries {
                if raster_bounds.len() >= max {
                    raster_bounds.clear();
                    self.platform_text_system.clear_glyph_raster_cache();
                }
            }
            let bounds = self.platform_text_system.glyph_raster_bounds(params)?;
            raster_bounds.insert(params.clone(), bounds);
            Ok(bounds)
        }
    }

    pub(crate) fn rasterize_glyph(
        &self,
        params: &RenderGlyphParams,
    ) -> Result<(Size<DevicePixels>, Vec<u8>)> {
        let raster_bounds = self.raster_bounds(params)?;
        self.platform_text_system
            .rasterize_glyph(params, raster_bounds)
    }
}

/// The GPUI text layout subsystem.
#[derive(Deref)]
pub struct WindowTextSystem {
    line_layout_cache: LineLayoutCache,
    #[deref]
    text_system: Arc<TextSystem>,
}

impl WindowTextSystem {
    #[doc(hidden)]
    pub fn new(text_system: Arc<TextSystem>) -> Self {
        Self {
            line_layout_cache: LineLayoutCache::new(
                text_system.platform_text_system.clone(),
                text_system.global_line_layout_cache.clone(),
                text_system.font_generation.clone(),
            ),
            text_system,
        }
    }

    pub(crate) fn layout_index(&self) -> LineLayoutIndex {
        self.line_layout_cache.layout_index()
    }

    pub(crate) fn reuse_layouts(&self, index: Range<LineLayoutIndex>) {
        self.line_layout_cache.reuse_layouts(index)
    }

    pub(crate) fn truncate_layouts(&self, index: LineLayoutIndex) {
        self.line_layout_cache.truncate_layouts(index)
    }

    /// Shape the given line, at the given font_size, for painting to the screen.
    /// Subsets of the line can be styled independently with the `runs` parameter.
    ///
    /// Note that this method can only shape a single line of text. It will panic
    /// if the text contains newlines. If you need to shape multiple lines of text,
    /// use [`Self::shape_text`] instead.
    pub fn shape_line(
        &self,
        text: SharedString,
        font_size: Pixels,
        runs: &[TextRun],
        force_width: Option<Pixels>,
    ) -> ShapedLine {
        self.shape_line_with_spacing(text, font_size, runs, force_width, None)
    }

    /// Shape a line of text with optional letter spacing applied to glyph positions.
    pub fn shape_line_with_spacing(
        &self,
        text: SharedString,
        font_size: Pixels,
        runs: &[TextRun],
        force_width: Option<Pixels>,
        letter_spacing: Option<Pixels>,
    ) -> ShapedLine {
        debug_assert!(
            text.find('\n').is_none(),
            "text argument should not contain newlines"
        );

        let mut decoration_runs = SmallVec::<[DecorationRun; 32]>::new();
        for run in runs {
            if let Some(last_run) = decoration_runs.last_mut()
                && last_run.color == run.color
                && last_run.underline == run.underline
                && last_run.strikethrough == run.strikethrough
                && last_run.background_color == run.background_color
            {
                last_run.len += run.len as u32;
                continue;
            }
            decoration_runs.push(DecorationRun {
                len: run.len as u32,
                color: run.color,
                background_color: run.background_color,
                underline: run.underline,
                strikethrough: run.strikethrough,
            });
        }

        let layout =
            self.layout_line_with_spacing(&text, font_size, runs, force_width, letter_spacing);

        ShapedLine {
            layout,
            text,
            decoration_runs,
        }
    }

    /// Shape a multi line string of text, at the given font_size, for painting to the screen.
    /// Subsets of the text can be styled independently with the `runs` parameter.
    /// If `wrap_width` is provided, the line breaks will be adjusted to fit within the given width.
    pub fn shape_text(
        &self,
        text: SharedString,
        font_size: Pixels,
        runs: &[TextRun],
        wrap_width: Option<Pixels>,
        line_clamp: Option<usize>,
    ) -> Result<SmallVec<[WrappedLine; 1]>> {
        let mut runs = runs.iter().filter(|run| run.len > 0).cloned().peekable();
        let mut font_runs = self.font_runs_pool.lock().pop().unwrap_or_default();

        let mut lines = SmallVec::new();
        let mut line_start = 0;
        let mut max_wrap_lines = line_clamp.unwrap_or(usize::MAX);
        let mut wrapped_lines = 0;

        let mut process_line = |line_text: SharedString| {
            font_runs.clear();
            let line_end = line_start + line_text.len();

            let mut last_font: Option<FontId> = None;
            let mut decoration_runs = SmallVec::<[DecorationRun; 32]>::new();
            let mut run_start = line_start;
            while run_start < line_end {
                let Some(run) = runs.peek_mut() else {
                    break;
                };

                let run_len_within_line = cmp::min(line_end, run_start + run.len) - run_start;

                let decoration_changed = if let Some(last_run) = decoration_runs.last_mut()
                    && last_run.color == run.color
                    && last_run.underline == run.underline
                    && last_run.strikethrough == run.strikethrough
                    && last_run.background_color == run.background_color
                {
                    last_run.len += run_len_within_line as u32;
                    false
                } else {
                    decoration_runs.push(DecorationRun {
                        len: run_len_within_line as u32,
                        color: run.color,
                        background_color: run.background_color,
                        underline: run.underline,
                        strikethrough: run.strikethrough,
                    });
                    true
                };

                if let Some(font_run) = font_runs.last_mut()
                    && Some(font_run.font_id) == last_font
                    && !decoration_changed
                {
                    font_run.len += run_len_within_line;
                } else {
                    let font_id = self.resolve_font(&run.font);
                    last_font = Some(font_id);
                    font_runs.push(FontRun {
                        len: run_len_within_line,
                        font_id,
                    });
                }

                if run_len_within_line == run.len {
                    runs.next();
                } else {
                    // Preserve the remainder of the run for the next line
                    run.len -= run_len_within_line;
                }
                run_start += run_len_within_line;
            }

            let layout = self.line_layout_cache.layout_wrapped_line(
                &line_text,
                font_size,
                &font_runs,
                wrap_width,
                Some(max_wrap_lines - wrapped_lines),
            );
            wrapped_lines += layout.wrap_boundaries.len();

            lines.push(WrappedLine {
                layout,
                decoration_runs,
                text: line_text,
            });

            // Skip `\n` character.
            line_start = line_end + 1;
            if let Some(run) = runs.peek_mut() {
                run.len -= 1;
                if run.len == 0 {
                    runs.next();
                }
            }
        };

        let mut split_lines = text.split('\n');
        let mut processed = false;

        if let Some(first_line) = split_lines.next()
            && let Some(second_line) = split_lines.next()
        {
            processed = true;
            process_line(first_line.to_string().into());
            process_line(second_line.to_string().into());
            for line_text in split_lines {
                process_line(line_text.to_string().into());
            }
        }

        if !processed {
            process_line(text);
        }

        self.font_runs_pool.lock().push(font_runs);

        Ok(lines)
    }

    pub(crate) fn finish_frame(&self) {
        self.line_layout_cache.finish_frame()
    }

    /// Layout the given line of text, at the given font_size.
    /// Subsets of the line can be styled independently with the `runs` parameter.
    /// Generally, you should prefer to use [`Self::shape_line`] instead, which
    /// can be painted directly.
    pub fn layout_line(
        &self,
        text: &str,
        font_size: Pixels,
        runs: &[TextRun],
        force_width: Option<Pixels>,
    ) -> Arc<LineLayout> {
        self.layout_line_with_spacing(text, font_size, runs, force_width, None)
    }

    /// Layout a line of text with optional letter spacing applied to glyph positions.
    pub fn layout_line_with_spacing(
        &self,
        text: &str,
        font_size: Pixels,
        runs: &[TextRun],
        force_width: Option<Pixels>,
        letter_spacing: Option<Pixels>,
    ) -> Arc<LineLayout> {
        let mut last_run = None::<&TextRun>;
        let mut last_font: Option<FontId> = None;
        let mut font_runs = self.font_runs_pool.lock().pop().unwrap_or_default();
        font_runs.clear();

        for run in runs.iter() {
            let decoration_changed = if let Some(last_run) = last_run
                && last_run.color == run.color
                && last_run.underline == run.underline
                && last_run.strikethrough == run.strikethrough
            {
                false
            } else {
                last_run = Some(run);
                true
            };

            if let Some(font_run) = font_runs.last_mut()
                && Some(font_run.font_id) == last_font
                && !decoration_changed
            {
                font_run.len += run.len;
            } else {
                let font_id = self.resolve_font(&run.font);
                last_font = Some(font_id);
                font_runs.push(FontRun {
                    len: run.len,
                    font_id,
                });
            }
        }

        let layout = self.line_layout_cache.layout_line_with_spacing(
            &SharedString::new(text),
            font_size,
            &font_runs,
            force_width,
            letter_spacing,
        );

        self.font_runs_pool.lock().push(font_runs);

        layout
    }
}

#[derive(Hash, Eq, PartialEq)]
struct FontIdWithSize {
    font_id: FontId,
    font_size: Pixels,
}

/// A handle into the text system, which can be used to compute the wrapped layout of text
pub struct LineWrapperHandle {
    wrapper: Option<LineWrapper>,
    text_system: Arc<TextSystem>,
}

impl Drop for LineWrapperHandle {
    fn drop(&mut self) {
        let mut state = self.text_system.wrapper_pool.lock();
        let wrapper = self.wrapper.take().unwrap();
        state
            .get_mut(&FontIdWithSize {
                font_id: wrapper.font_id,
                font_size: wrapper.font_size,
            })
            .unwrap()
            .push(wrapper);
    }
}

impl Deref for LineWrapperHandle {
    type Target = LineWrapper;

    fn deref(&self) -> &Self::Target {
        self.wrapper.as_ref().unwrap()
    }
}

impl DerefMut for LineWrapperHandle {
    fn deref_mut(&mut self) -> &mut Self::Target {
        self.wrapper.as_mut().unwrap()
    }
}

/// The degree of blackness or stroke thickness of a font. This value ranges from 100.0 to 900.0,
/// with 400.0 as normal.
#[derive(Clone, Copy, Debug, PartialEq, PartialOrd, Serialize, Deserialize, Add, Sub, FromStr)]
#[serde(transparent)]
pub struct FontWeight(pub f32);

impl Display for FontWeight {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.0)
    }
}

impl From<f32> for FontWeight {
    fn from(weight: f32) -> Self {
        FontWeight(weight)
    }
}

impl Default for FontWeight {
    #[inline]
    fn default() -> FontWeight {
        FontWeight::NORMAL
    }
}

impl Hash for FontWeight {
    fn hash<H: Hasher>(&self, state: &mut H) {
        state.write_u32(u32::from_be_bytes(self.0.to_be_bytes()));
    }
}

impl Eq for FontWeight {}

impl FontWeight {
    /// Thin weight (100), the thinnest value.
    pub const THIN: FontWeight = FontWeight(100.0);
    /// Extra light weight (200).
    pub const EXTRA_LIGHT: FontWeight = FontWeight(200.0);
    /// Light weight (300).
    pub const LIGHT: FontWeight = FontWeight(300.0);
    /// Normal (400).
    pub const NORMAL: FontWeight = FontWeight(400.0);
    /// Medium weight (500, higher than normal).
    pub const MEDIUM: FontWeight = FontWeight(500.0);
    /// Semibold weight (600).
    pub const SEMIBOLD: FontWeight = FontWeight(600.0);
    /// Bold weight (700).
    pub const BOLD: FontWeight = FontWeight(700.0);
    /// Extra-bold weight (800).
    pub const EXTRA_BOLD: FontWeight = FontWeight(800.0);
    /// Black weight (900), the thickest value.
    pub const BLACK: FontWeight = FontWeight(900.0);

    /// All of the font weights, in order from thinnest to thickest.
    pub const ALL: [FontWeight; 9] = [
        Self::THIN,
        Self::EXTRA_LIGHT,
        Self::LIGHT,
        Self::NORMAL,
        Self::MEDIUM,
        Self::SEMIBOLD,
        Self::BOLD,
        Self::EXTRA_BOLD,
        Self::BLACK,
    ];
}

impl schemars::JsonSchema for FontWeight {
    fn schema_name() -> std::borrow::Cow<'static, str> {
        "FontWeight".into()
    }

    fn json_schema(_: &mut schemars::SchemaGenerator) -> schemars::Schema {
        use schemars::json_schema;
        json_schema!({
            "type": "number",
            "minimum": Self::THIN,
            "maximum": Self::BLACK,
            "default": Self::default(),
            "description": "Font weight value between 100 (thin) and 900 (black)"
        })
    }
}

/// Allows italic or oblique faces to be selected.
#[derive(Clone, Copy, Eq, PartialEq, Debug, Hash, Default, Serialize, Deserialize, JsonSchema)]
pub enum FontStyle {
    /// A face that is neither italic not obliqued.
    #[default]
    Normal,
    /// A form that is generally cursive in nature.
    Italic,
    /// A typically-sloped version of the regular face.
    Oblique,
}

impl Display for FontStyle {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        Debug::fmt(self, f)
    }
}

/// A styled run of text, for use in [`crate::TextLayout`].
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct TextRun {
    /// A number of utf8 bytes
    pub len: usize,
    /// The font to use for this run.
    pub font: Font,
    /// The color
    pub color: Hsla,
    /// The background color (if any)
    pub background_color: Option<Hsla>,
    /// The underline style (if any)
    pub underline: Option<UnderlineStyle>,
    /// The strikethrough style (if any)
    pub strikethrough: Option<StrikethroughStyle>,
}

#[cfg(all(target_os = "macos", test))]
impl TextRun {
    fn with_len(&self, len: usize) -> Self {
        let mut this = self.clone();
        this.len = len;
        this
    }
}

/// An identifier for a specific glyph, as returned by [`WindowTextSystem::layout_line`].
#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
#[repr(C)]
pub struct GlyphId(pub u32);

#[derive(Clone, Debug, PartialEq)]
#[allow(missing_docs)]
pub struct RenderGlyphParams {
    pub font_id: FontId,
    pub glyph_id: GlyphId,
    pub font_size: Pixels,
    pub subpixel_variant: Point<u8>,
    pub scale_factor: f32,
    pub is_emoji: bool,
    pub dilation: u8,
}

impl Eq for RenderGlyphParams {}

impl Hash for RenderGlyphParams {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.font_id.0.hash(state);
        self.glyph_id.0.hash(state);
        self.font_size.0.to_bits().hash(state);
        self.subpixel_variant.hash(state);
        self.scale_factor.to_bits().hash(state);
        self.is_emoji.hash(state);
        self.dilation.hash(state);
    }
}

/// The configuration details for identifying a specific font.
#[derive(Clone, Debug, Eq, PartialEq, Hash)]
pub struct Font {
    /// The font family name.
    ///
    /// The special name ".SystemUIFont" is used to identify the system UI font, which varies based on platform.
    pub family: SharedString,

    /// The font features to use.
    pub features: FontFeatures,

    /// The fallbacks fonts to use.
    pub fallbacks: Option<FontFallbacks>,

    /// The font weight.
    pub weight: FontWeight,

    /// The font style.
    pub style: FontStyle,
}

/// Get a [`Font`] for a given name.
pub fn font(family: impl Into<SharedString>) -> Font {
    Font {
        family: family.into(),
        features: FontFeatures::default(),
        weight: FontWeight::default(),
        style: FontStyle::default(),
        fallbacks: None,
    }
}

impl Font {
    /// Set this Font to be bold
    pub fn bold(mut self) -> Self {
        self.weight = FontWeight::BOLD;
        self
    }

    /// Set this Font to be italic
    pub fn italic(mut self) -> Self {
        self.style = FontStyle::Italic;
        self
    }
}

/// A struct for storing font metrics.
/// It is used to define the measurements of a typeface.
#[derive(Clone, Copy, Debug)]
pub struct FontMetrics {
    /// The number of font units that make up the "em square",
    /// a scalable grid for determining the size of a typeface.
    pub units_per_em: u32,

    /// The vertical distance from the baseline of the font to the top of the glyph covers.
    pub ascent: f32,

    /// The vertical distance from the baseline of the font to the bottom of the glyph covers.
    pub descent: f32,

    /// The recommended additional space to add between lines of type.
    pub line_gap: f32,

    /// The suggested position of the underline.
    pub underline_position: f32,

    /// The suggested thickness of the underline.
    pub underline_thickness: f32,

    /// The height of a capital letter measured from the baseline of the font.
    pub cap_height: f32,

    /// The height of a lowercase x.
    pub x_height: f32,

    /// The outer limits of the area that the font covers.
    /// Corresponds to the xMin / xMax / yMin / yMax values in the OpenType `head` table
    pub bounding_box: Bounds<f32>,
}

impl FontMetrics {
    /// Returns the vertical distance from the baseline of the font to the top of the glyph covers in pixels.
    pub fn ascent(&self, font_size: Pixels) -> Pixels {
        Pixels((self.ascent / self.units_per_em as f32) * font_size.0)
    }

    /// Returns the vertical distance from the baseline of the font to the bottom of the glyph covers in pixels.
    pub fn descent(&self, font_size: Pixels) -> Pixels {
        Pixels((self.descent / self.units_per_em as f32) * font_size.0)
    }

    /// Returns the recommended additional space to add between lines of type in pixels.
    pub fn line_gap(&self, font_size: Pixels) -> Pixels {
        Pixels((self.line_gap / self.units_per_em as f32) * font_size.0)
    }

    /// Returns the suggested position of the underline in pixels.
    pub fn underline_position(&self, font_size: Pixels) -> Pixels {
        Pixels((self.underline_position / self.units_per_em as f32) * font_size.0)
    }

    /// Returns the suggested thickness of the underline in pixels.
    pub fn underline_thickness(&self, font_size: Pixels) -> Pixels {
        Pixels((self.underline_thickness / self.units_per_em as f32) * font_size.0)
    }

    /// Returns the height of a capital letter measured from the baseline of the font in pixels.
    pub fn cap_height(&self, font_size: Pixels) -> Pixels {
        Pixels((self.cap_height / self.units_per_em as f32) * font_size.0)
    }

    /// Returns the height of a lowercase x in pixels.
    pub fn x_height(&self, font_size: Pixels) -> Pixels {
        Pixels((self.x_height / self.units_per_em as f32) * font_size.0)
    }

    /// Returns the outer limits of the area that the font covers in pixels.
    pub fn bounding_box(&self, font_size: Pixels) -> Bounds<Pixels> {
        (self.bounding_box / self.units_per_em as f32 * font_size.0).map(px)
    }
}

#[allow(unused)]
#[doc(hidden)]
pub fn font_name_with_fallbacks<'a>(name: &'a str, system: &'a str) -> &'a str {
    // Note: the "Zed Plex" fonts were deprecated as we are not allowed to use "Plex"
    // in a derived font name. They are essentially indistinguishable from IBM Plex/Lilex,
    // and so retained here for backward compatibility.
    match name {
        ".SystemUIFont" => system,
        ".ZedSans" | "Zed Plex Sans" => "IBM Plex Sans",
        ".ZedMono" | "Zed Plex Mono" => "Lilex",
        _ => name,
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{AppResourceProfile, NoopTextSystem, point, size};
    use parking_lot::Mutex;
    use std::collections::HashSet;
    use std::sync::atomic::AtomicBool;

    struct TrackingTextSystem {
        noop: NoopTextSystem,
        pending_glyph_images: Mutex<HashSet<RenderGlyphParams>>,
        missing_glyph_sink_installed: AtomicBool,
    }

    impl TrackingTextSystem {
        fn new() -> Self {
            Self {
                noop: NoopTextSystem::new(),
                pending_glyph_images: Mutex::default(),
                missing_glyph_sink_installed: AtomicBool::new(false),
            }
        }

        fn pending_glyph_images_len(&self) -> usize {
            self.pending_glyph_images.lock().len()
        }
    }

    impl PlatformTextSystem for TrackingTextSystem {
        fn set_missing_glyph_sink(&self, _sink: Arc<dyn MissingGlyphSink>) {
            self.missing_glyph_sink_installed
                .store(true, Ordering::SeqCst);
        }

        fn add_fonts(&self, fonts: Vec<Cow<'static, [u8]>>) -> Result<()> {
            self.noop.add_fonts(fonts)
        }

        fn all_font_names(&self) -> Vec<String> {
            self.noop.all_font_names()
        }

        fn font_id(&self, descriptor: &Font) -> Result<FontId> {
            self.noop.font_id(descriptor)
        }

        fn clear_glyph_raster_cache(&self) {
            self.pending_glyph_images.lock().clear();
        }

        fn font_metrics(&self, font_id: FontId) -> FontMetrics {
            self.noop.font_metrics(font_id)
        }

        fn typographic_bounds(&self, font_id: FontId, glyph_id: GlyphId) -> Result<Bounds<f32>> {
            self.noop.typographic_bounds(font_id, glyph_id)
        }

        fn advance(&self, font_id: FontId, glyph_id: GlyphId) -> Result<Size<f32>> {
            self.noop.advance(font_id, glyph_id)
        }

        fn glyph_for_char(&self, font_id: FontId, ch: char) -> Option<GlyphId> {
            self.noop.glyph_for_char(font_id, ch)
        }

        fn glyph_raster_bounds(&self, params: &RenderGlyphParams) -> Result<Bounds<DevicePixels>> {
            self.pending_glyph_images.lock().insert(params.clone());
            Ok(Bounds {
                origin: point(DevicePixels(0), DevicePixels(0)),
                size: size(DevicePixels(1), DevicePixels(1)),
            })
        }

        fn rasterize_glyph(
            &self,
            params: &RenderGlyphParams,
            raster_bounds: Bounds<DevicePixels>,
        ) -> Result<(Size<DevicePixels>, Vec<u8>)> {
            self.pending_glyph_images.lock().remove(params);
            Ok((raster_bounds.size, vec![0]))
        }

        fn layout_line(&self, text: &str, font_size: Pixels, runs: &[FontRun]) -> LineLayout {
            self.noop.layout_line(text, font_size, runs)
        }
    }

    fn glyph_params(glyph_id: u32) -> RenderGlyphParams {
        RenderGlyphParams {
            font_id: FontId(0),
            glyph_id: GlyphId(glyph_id),
            font_size: px(16.),
            subpixel_variant: point(0, 0),
            scale_factor: 1.0,
            is_emoji: false,
            dilation: 0,
        }
    }

    #[test]
    fn all_font_names_lists_only_platform_families() {
        let text_system = TextSystem::new(
            Arc::new(NoopTextSystem::new()),
            &AppResourceProfile::desktop().text,
        );
        assert!(text_system.all_font_names().is_empty());
    }

    #[test]
    fn text_system_installs_missing_glyph_sink_on_platform() {
        let platform = Arc::new(TrackingTextSystem::new());
        assert!(!platform.missing_glyph_sink_installed.load(Ordering::SeqCst));
        let _text_system = TextSystem::new(platform.clone(), &AppResourceProfile::desktop().text);
        assert!(platform.missing_glyph_sink_installed.load(Ordering::SeqCst));
    }

    #[test]
    fn clearing_layout_cache_also_clears_platform_pending_glyph_images() {
        let platform = Arc::new(TrackingTextSystem::new());
        let text_system = TextSystem::new(platform.clone(), &AppResourceProfile::desktop().text);

        text_system.raster_bounds(&glyph_params(1)).unwrap();
        assert_eq!(platform.pending_glyph_images_len(), 1);

        text_system.clear_layout_cache();

        assert_eq!(platform.pending_glyph_images_len(), 0);
    }

    #[test]
    fn evicting_raster_bounds_also_clears_platform_pending_glyph_images() {
        let platform = Arc::new(TrackingTextSystem::new());
        let mut budget = AppResourceProfile::desktop().text;
        budget.raster_bounds_cache_max_entries = Some(1);
        let text_system = TextSystem::new(platform.clone(), &budget);

        text_system.raster_bounds(&glyph_params(1)).unwrap();
        text_system.raster_bounds(&glyph_params(2)).unwrap();

        assert_eq!(platform.pending_glyph_images_len(), 1);
    }

    #[test]
    fn adding_fonts_invalidates_cached_line_layouts() {
        let text_system = Arc::new(TextSystem::new(
            Arc::new(NoopTextSystem::new()),
            &AppResourceProfile::desktop().text,
        ));
        let window_text_system = WindowTextSystem::new(text_system.clone());
        let text: SharedString = "cached text".into();
        let runs = [TextRun {
            len: text.len(),
            font: font("IBM Plex Sans"),
            color: Default::default(),
            background_color: None,
            underline: None,
            strikethrough: None,
        }];

        let first_layout = window_text_system.shape_line(text.clone(), px(14.0), &runs, None);
        let cached_layout = window_text_system.shape_line(text.clone(), px(14.0), &runs, None);
        assert!(std::ptr::eq::<LineLayout>(
            &**first_layout,
            &**cached_layout
        ));

        text_system
            .add_fonts(vec![Cow::Borrowed(b"unused")])
            .unwrap();

        let refreshed_layout = window_text_system.shape_line(text, px(14.0), &runs, None);
        assert!(!std::ptr::eq::<LineLayout>(
            &**first_layout,
            &**refreshed_layout
        ));
    }

    #[test]
    fn test_font_weight_from_str() {
        let weight: FontWeight = "450".parse().unwrap();
        assert_eq!(weight, FontWeight(450.0));
        assert!("not-a-number".parse::<FontWeight>().is_err());
        assert_eq!(weight + FontWeight(50.0), FontWeight(500.0));
        assert_eq!(weight - FontWeight(50.0), FontWeight(400.0));
    }
}

#[cfg(test)]
mod missing_glyph_tests {
    use super::*;
    use crate::{AppResourceProfile, NoopTextSystem};
    use futures::FutureExt as _;

    #[test]
    fn bounds_retained_missing_glyphs() {
        let (reporter, mut receiver) = missing_glyph_channel();
        reporter.report(
            (0..MAX_REPORTED_MISSING_GLYPHS)
                .map(|index| {
                    MissingGlyph::new(index.to_string().into(), FallbackFontClass::Proportional)
                })
                .collect(),
        );
        assert!(receiver.recv().now_or_never().unwrap().is_ok());

        let newest = MissingGlyph::new("newest".into(), FallbackFontClass::Monospace);
        reporter.report(vec![newest.clone()]);
        assert!(receiver.recv().now_or_never().unwrap().is_ok());

        let state = &receiver.state;
        assert_eq!(state.reported.len(), MAX_REPORTED_MISSING_GLYPHS);
        assert_eq!(state.reported_order.len(), MAX_REPORTED_MISSING_GLYPHS);
        assert!(state.reported.contains(&newest));
    }

    #[test]
    fn dropping_receiver_closes_and_clears_reports() {
        let (reporter, receiver) = missing_glyph_channel();
        reporter.report(vec![missing_glyph("missing")]);

        drop(receiver);

        assert!(reporter.sender.is_closed());
        assert!(reporter.sender.is_empty());
    }

    #[test]
    fn text_system_delivers_reported_missing_glyphs() {
        let text_system = TextSystem::new(
            Arc::new(NoopTextSystem::new()),
            &AppResourceProfile::desktop().text,
        );
        let mut receiver = text_system.take_missing_glyph_receiver().expect("receiver");
        text_system.report_missing_glyphs_in_test(vec![missing_glyph("界")]);

        let received = receiver.recv().now_or_never().unwrap().unwrap();
        assert_eq!(received.len(), 1);
        assert_eq!(received[0].grapheme(), "界");
        assert!(text_system.take_missing_glyph_receiver().is_none());
    }

    fn missing_glyph_channel() -> (MissingGlyphReporter, MissingGlyphReceiver) {
        let (sender, receiver) = async_channel::bounded(MAX_REPORTED_MISSING_GLYPHS);
        let generation = Arc::<AtomicUsize>::default();
        let reporter = MissingGlyphReporter {
            generation: generation.clone(),
            sender,
        };
        let receiver = MissingGlyphReceiver {
            state: MissingGlyphState::default(),
            generation,
            receiver,
        };
        (reporter, receiver)
    }

    fn missing_glyph(grapheme: &'static str) -> MissingGlyph {
        MissingGlyph::new(grapheme.into(), FallbackFontClass::Proportional)
    }
}