iris/core/src/primitive/text.rs

#[cfg(feature = "layout-diagnostics")]
use crate::layout_diagnostics::{self as diag, Counter, TimerKind};
use crate::{
    Align, GlyphAtlas, GlyphEntry, GlyphKey, PlacedGlyph, Px, PxVec2, RegionAlign, UiColor,
    util::Vec2,
};
use parley::{
    Alignment, AlignmentOptions, FontContext, FontFamily, FontFamilyName, GenericFamily, Layout,
    LayoutContext, LineHeight, PositionedLayoutItem, StyleProperty,
};
use std::{
    collections::VecDeque,
    hash::{DefaultHasher, Hash, Hasher},
};
use swash::{
    FontRef,
    scale::{Render, ScaleContext, Source, StrikeWith},
    zeno::{Format, Vector},
};

pub struct TextData {
    pub font_ctx: FontContext,
    pub layout_ctx: LayoutContext<UiColor>,
    scale_ctx: ScaleContext,
    pub atlas: GlyphAtlas,
    spare: VecDeque<Placed>,
}

/// The glyphs of one text at one width. A buffer holds the ones it is drawn
/// as; these are the ones it had before, kept because a container measures a
/// child by drawing it in a box it may not keep, and so comes back to widths
/// it has already asked for.
struct Placed {
    /// Where the glyphs land is a function of these three and nothing else,
    /// so no widget or buffer identity is involved and two texts of the same
    /// words share an answer.
    text: String,
    key: LayoutKey,
    glyphs: RenderedText,
}

/// How many to keep. Bounding the whole store rather than each buffer is what
/// makes this a fixed cost instead of one a tree of ten thousand texts pays
/// ten thousand times; the re-asks come from laying out one subtree, so they
/// are close together and few are needed. Instructions over 500 resize frames
/// of `tests/revision_cost.rs`, both the repeating widths and the sweep that
/// cannot hit across frames: 13.7B at 32, 12.1B at 64, 10.4B and 12.1B at 128,
/// and nothing past that -- so 128, which is no worse in the case that never
/// repeats and better in the one that does.
const SPARE_PLACED: usize = 128;

impl Default for TextData {
    fn default() -> Self {
        Self {
            font_ctx: FontContext::new(),
            layout_ctx: LayoutContext::new(),
            scale_ctx: ScaleContext::new(),
            atlas: GlyphAtlas::default(),
            spare: VecDeque::new(),
        }
    }
}

#[derive(Clone, PartialEq)]
pub enum Family {
    SansSerif,
    Serif,
    Monospace,
    Named(String),
}

impl Family {
    fn family(&self) -> FontFamily<'_> {
        let name = match self {
            Self::SansSerif => FontFamilyName::Generic(GenericFamily::SansSerif),
            Self::Serif => FontFamilyName::Generic(GenericFamily::Serif),
            Self::Monospace => FontFamilyName::Generic(GenericFamily::Monospace),
            Self::Named(name) => FontFamilyName::Named(name.as_str().into()),
        };
        FontFamily::Single(name)
    }
}

#[derive(Clone, PartialEq)]
pub struct TextAttrs {
    pub color: UiColor,
    pub font_size: f32,
    pub line_height: f32,
    pub family: Family,
    pub wrap: bool,
    pub align: RegionAlign,
}

pub const LINE_HEIGHT_MULT: f32 = 1.1;

impl Default for TextAttrs {
    fn default() -> Self {
        let size = 16.0;
        Self {
            color: UiColor::WHITE,
            font_size: size,
            line_height: size * LINE_HEIGHT_MULT,
            family: Family::SansSerif,
            wrap: false,
            align: Align::CENTER_LEFT,
        }
    }
}

/// Keeps text and its corresponding layout from getting out of sync.
pub struct TextBuffer {
    text: String,
    layout: Layout<UiColor>,
    layout_key: Option<LayoutKey>,
    /// The glyphs placed from `layout`, so drawing this text again at the
    /// width it already has places them once.
    placed: Option<RenderedText>,
}

#[derive(PartialEq)]
struct LayoutKey {
    attrs: TextAttrs,
    max_width: Option<f32>,
}

impl TextBuffer {
    pub fn new(text: impl Into<String>) -> Self {
        Self {
            text: text.into(),
            layout: Layout::new(),
            layout_key: None,
            placed: None,
        }
    }

    pub fn text(&self) -> &str {
        &self.text
    }

    pub fn layout(&self) -> &Layout<UiColor> {
        &self.layout
    }

    pub fn is_empty(&self) -> bool {
        self.text.is_empty()
    }

    pub fn set_text(&mut self, text: impl Into<String>) {
        let text = text.into();
        if text != self.text {
            self.text = text;
            self.layout_key = None;
            self.placed = None;
        }
    }

    /// Invalidates the layout and returns the underlying string for editing.
    pub fn edit(&mut self) -> &mut String {
        self.layout_key = None;
        self.placed = None;
        &mut self.text
    }

    /// The glyphs of the shaping it is drawn as, once they are placed.
    pub fn rendered(&self) -> Option<&RenderedText> {
        self.placed.as_ref()
    }

    /// The width its shaping wraps at, and `None` where it does not wrap or
    /// has not been shaped.
    pub fn wrap_width(&self) -> Option<f32> {
        self.layout_key.as_ref()?.max_width
    }

    /// Widths covered by the current line breaks, including a wider shaping
    /// retained when a later draw requested a narrower box.
    pub fn width_holds(&self) -> crate::Holds {
        let Some(width) = self.wrap_width() else {
            return crate::Holds::ANY;
        };
        let width = Px::from_f32(width);
        let soft_wrapped = self.layout.lines().any(|line| {
            matches!(
                line.break_reason(),
                parley::layout::BreakReason::Regular | parley::layout::BreakReason::Emergency
            )
        });
        let upper = if soft_wrapped { width } else { Px::MAX };
        crate::Holds::from(Px::ceil_from_f32(self.layout.width()).min(width)..=upper)
    }

    pub fn size(&self) -> Vec2 {
        Vec2::new(self.layout.width(), self.layout.height())
    }

    pub fn shape(&mut self, data: &mut TextData, attrs: &TextAttrs, width: Option<f32>) {
        let layout_key = LayoutKey {
            attrs: attrs.clone(),
            max_width: width,
        };
        if self.layout_key.as_ref() == Some(&layout_key) {
            #[cfg(feature = "layout-diagnostics")]
            diag::bump(Counter::TextShapeHits);
            return;
        }
        // A greedy break at one width is the same break at every width down
        // to the longest line it produced: each line still fits, and none can
        // take a word that would not fit in the wider box. So the layout in
        // hand already answers, and re-breaking would only be work.
        //
        // At the longest line exactly, with no margin below it. A narrower
        // width really does break differently, so answering one from the
        // break in hand is how a warm tree keeps lines a cold tree would
        // never produce. The margin was here because a text reports the
        // width it used and a parent hands that back; the report is the step
        // at or above its longest line now, so what comes back fits.
        if let Some(key) = &self.layout_key
            && key.attrs == *attrs
            && let (Some(broke_at), Some(want)) = (key.max_width, width)
            && want <= broke_at
            && want >= self.layout.width()
        {
            #[cfg(feature = "layout-diagnostics")]
            diag::bump(Counter::TextShapeHits);
            return;
        }
        let same_shaping = self
            .layout_key
            .as_ref()
            .is_some_and(|key| key.attrs == *attrs);
        let old_key = self.layout_key.replace(layout_key);
        // The glyphs it holds are of the width it held, which the layout may
        // well come back to.
        if let Some(key) = old_key
            && let Some(glyphs) = self.placed.take()
        {
            data.keep_placed(Placed {
                text: self.text.clone(),
                key,
                glyphs,
            });
        }
        // Only the line breaking depends on the width: the shaped runs under
        // it are a function of the text and the attrs, and parley re-breaks
        // them in place. So a new width is a break, not a shaping.
        if same_shaping {
            #[cfg(feature = "layout-diagnostics")]
            diag::bump(Counter::TextBreaks);
            #[cfg(feature = "layout-diagnostics")]
            let _break = diag::timer(TimerKind::TextBreak);
            self.break_lines(width);
            return;
        }
        #[cfg(feature = "layout-diagnostics")]
        diag::bump(Counter::TextShapes);
        #[cfg(feature = "layout-diagnostics")]
        let _shape = diag::timer(TimerKind::TextShape);
        let mut builder = data
            .layout_ctx
            .ranged_builder(&mut data.font_ctx, &self.text, 1.0, true);
        builder.push_default(StyleProperty::FontFamily(attrs.family.family()));
        builder.push_default(StyleProperty::FontSize(attrs.font_size));
        builder.push_default(StyleProperty::LineHeight(LineHeight::Absolute(
            attrs.line_height,
        )));
        builder.push_default(StyleProperty::Brush(attrs.color));
        builder.build_into(&mut self.layout, &self.text);
        self.break_lines(width);
    }

    fn break_lines(&mut self, width: Option<f32>) {
        self.layout.break_all_lines(width);
        self.layout
            .align(Alignment::Start, AlignmentOptions::default());
    }
}

impl TextData {
    pub fn place(&mut self, buffer: &TextBuffer) -> Vec<PlacedGlyph> {
        let mut placed = Vec::new();
        for line in buffer.layout.lines() {
            for item in line.items() {
                let PositionedLayoutItem::GlyphRun(run) = item else {
                    continue;
                };
                let font = run.run().font();
                let font_size = run.run().font_size();
                let coords = run.run().normalized_coords();
                let Some(font_ref) = FontRef::from_index(font.data.as_ref(), font.index as usize)
                else {
                    continue;
                };
                let coords_hash = hash_coords(coords);
                let font_id = font.data.id();

                for glyph in run.positioned_glyphs() {
                    let subpixel = ((glyph.x.fract() * 4.0).round() as i32).rem_euclid(4) as u8;
                    let key = GlyphKey {
                        font: font_id,
                        glyph: glyph.id,
                        size: glyph_size_key(font_size),
                        subpixel,
                        coords: coords_hash,
                    };
                    let Some(entry) = self.glyph_entry(GlyphRaster {
                        key,
                        font: font_ref,
                        font_size,
                        coords,
                        subpixel,
                        glyph_id: glyph.id,
                    }) else {
                        continue;
                    };
                    placed.push(PlacedGlyph {
                        entry,
                        offset: PxVec2::new(
                            Px::from_int(glyph.x.floor() as i32 + entry.left),
                            Px::from_int(glyph.y.floor() as i32 - entry.top),
                        ),
                    });
                }
            }
        }
        placed
    }

    fn glyph_entry(&mut self, glyph: GlyphRaster<'_>) -> Option<GlyphEntry> {
        if let Some(entry) = self.atlas.get(&glyph.key) {
            return entry;
        }

        let mut scaler = self
            .scale_ctx
            .builder(glyph.font)
            .size(glyph.font_size)
            .hint(true)
            .normalized_coords(glyph.coords)
            .build();
        let image = Render::new(&[
            Source::ColorOutline(0),
            Source::ColorBitmap(StrikeWith::BestFit),
            Source::Outline,
        ])
        .format(Format::Alpha)
        .offset(Vector::new(glyph.subpixel as f32 / 4.0, 0.0))
        .render(&mut scaler, glyph.glyph_id as u16);

        if let Some(image) = image {
            self.atlas.insert(glyph.key, &image)
        } else {
            self.atlas.insert_empty(glyph.key);
            None
        }
    }
}

struct GlyphRaster<'a> {
    key: GlyphKey,
    font: FontRef<'a>,
    font_size: f32,
    coords: &'a [i16],
    subpixel: u8,
    glyph_id: u32,
}

fn hash_coords(coords: &[i16]) -> u64 {
    let mut hasher = DefaultHasher::new();
    coords.hash(&mut hasher);
    hasher.finish()
}

const GLYPH_SIZE_STEPS_PER_PIXEL: f32 = 16.0;

fn glyph_size_key(font_size: f32) -> u32 {
    (font_size * GLYPH_SIZE_STEPS_PER_PIXEL).round() as u32
}

pub struct RenderedText {
    pub glyphs: Vec<PlacedGlyph>,
    pub size: Vec2,
    pub color: UiColor,
}

impl TextData {
    /// The glyphs of this text at this width, taken out of what is kept.
    fn take_placed(&mut self, text: &str, key: &LayoutKey) -> Option<RenderedText> {
        // From the newest, since a re-ask is usually of something recent.
        let at = self
            .spare
            .iter()
            .rposition(|spare| spare.key == *key && spare.text == text)?;
        self.spare.remove(at).map(|spare| spare.glyphs)
    }

    fn keep_placed(&mut self, placed: Placed) {
        if self.spare.len() >= SPARE_PLACED {
            self.spare.pop_front();
        }
        self.spare.push_back(placed);
    }

    pub fn render<'b>(
        &mut self,
        buffer: &'b mut TextBuffer,
        attrs: &TextAttrs,
        width: Option<f32>,
    ) -> &'b RenderedText {
        #[cfg(feature = "layout-diagnostics")]
        diag::bump(Counter::TextRenders);
        #[cfg(feature = "layout-diagnostics")]
        let _render = diag::timer(TimerKind::TextRender);
        buffer.shape(self, attrs, width);
        // Only asked for when the buffer no longer holds them: taking one out
        // of the store to then drop it would throw an answer away.
        let placed = buffer.placed.take().or_else(|| {
            let key = buffer.layout_key.as_ref()?;
            self.take_placed(&buffer.text, key)
        });
        let placed = match placed {
            Some(placed) => placed,
            None => {
                #[cfg(feature = "layout-diagnostics")]
                diag::bump(Counter::GlyphPlacements);
                #[cfg(feature = "layout-diagnostics")]
                let _place = diag::timer(TimerKind::GlyphPlacement);
                RenderedText {
                    glyphs: self.place(buffer),
                    size: buffer.size(),
                    color: attrs.color,
                }
            }
        };
        buffer.placed.insert(placed)
    }
}