bevy/crates/bevy_text/src/glyph_brush.rs

use ab_glyph::{Font as _, FontArc, Glyph, ScaleFont as _};
use bevy_asset::{Assets, Handle};
use bevy_math::{Size, Vec2};
use bevy_render::texture::Image;
use bevy_sprite::TextureAtlas;
use glyph_brush_layout::{
    FontId, GlyphPositioner, Layout, SectionGeometry, SectionGlyph, SectionText, ToSectionText,
};

use crate::{error::TextError, Font, FontAtlasSet, GlyphAtlasInfo, TextAlignment};

pub struct GlyphBrush {
    fonts: Vec<FontArc>,
    handles: Vec<Handle<Font>>,
    latest_font_id: FontId,
}

impl Default for GlyphBrush {
    fn default() -> Self {
        GlyphBrush {
            fonts: Vec::new(),
            handles: Vec::new(),
            latest_font_id: FontId(0),
        }
    }
}

impl GlyphBrush {
    pub fn compute_glyphs<S: ToSectionText>(
        &self,
        sections: &[S],
        bounds: Size,
        text_alignment: TextAlignment,
    ) -> Result<Vec<SectionGlyph>, TextError> {
        let geom = SectionGeometry {
            bounds: (bounds.width, bounds.height),
            ..Default::default()
        };
        let section_glyphs = Layout::default()
            .h_align(text_alignment.horizontal.into())
            .v_align(text_alignment.vertical.into())
            .calculate_glyphs(&self.fonts, &geom, sections);
        Ok(section_glyphs)
    }

    pub fn process_glyphs(
        &self,
        glyphs: Vec<SectionGlyph>,
        sections: &[SectionText],
        font_atlas_set_storage: &mut Assets<FontAtlasSet>,
        fonts: &Assets<Font>,
        texture_atlases: &mut Assets<TextureAtlas>,
        textures: &mut Assets<Image>,
    ) -> Result<Vec<PositionedGlyph>, TextError> {
        if glyphs.is_empty() {
            return Ok(Vec::new());
        }

        let sections_data = sections
            .iter()
            .map(|section| {
                let handle = &self.handles[section.font_id.0];
                let font = fonts.get(handle).ok_or(TextError::NoSuchFont)?;
                let font_size = section.scale.y;
                Ok((
                    handle,
                    font,
                    font_size,
                    ab_glyph::Font::as_scaled(&font.font, font_size),
                ))
            })
            .collect::<Result<Vec<_>, _>>()?;

        let mut max_y = std::f32::MIN;
        let mut min_x = std::f32::MAX;
        for sg in &glyphs {
            let glyph = &sg.glyph;
            let scaled_font = sections_data[sg.section_index].3;
            max_y = max_y.max(glyph.position.y - scaled_font.descent());
            min_x = min_x.min(glyph.position.x);
        }
        max_y = max_y.floor();
        min_x = min_x.floor();

        let mut positioned_glyphs = Vec::new();
        for sg in glyphs {
            let SectionGlyph {
                section_index: _,
                byte_index,
                mut glyph,
                font_id: _,
            } = sg;
            let glyph_id = glyph.id;
            let glyph_position = glyph.position;
            let adjust = GlyphPlacementAdjuster::new(&mut glyph);
            let section_data = sections_data[sg.section_index];
            if let Some(outlined_glyph) = section_data.1.font.outline_glyph(glyph) {
                let bounds = outlined_glyph.px_bounds();
                let handle_font_atlas: Handle<FontAtlasSet> = section_data.0.as_weak();
                let font_atlas_set = font_atlas_set_storage
                    .get_or_insert_with(handle_font_atlas, FontAtlasSet::default);

                let atlas_info = font_atlas_set
                    .get_glyph_atlas_info(section_data.2, glyph_id, glyph_position)
                    .map(Ok)
                    .unwrap_or_else(|| {
                        font_atlas_set.add_glyph_to_atlas(texture_atlases, textures, outlined_glyph)
                    })?;

                let texture_atlas = texture_atlases.get(&atlas_info.texture_atlas).unwrap();
                let glyph_rect = texture_atlas.textures[atlas_info.glyph_index as usize];
                let size = Vec2::new(glyph_rect.width(), glyph_rect.height());

                let x = bounds.min.x + size.x / 2.0 - min_x;
                let y = max_y - bounds.max.y + size.y / 2.0;
                let position = adjust.position(Vec2::new(x, y));

                positioned_glyphs.push(PositionedGlyph {
                    position,
                    size,
                    atlas_info,
                    section_index: sg.section_index,
                    byte_index,
                });
            }
        }
        Ok(positioned_glyphs)
    }

    pub fn add_font(&mut self, handle: Handle<Font>, font: FontArc) -> FontId {
        self.fonts.push(font);
        self.handles.push(handle);
        let font_id = self.latest_font_id;
        self.latest_font_id = FontId(font_id.0 + 1);
        font_id
    }
}

#[derive(Debug, Clone)]
pub struct PositionedGlyph {
    pub position: Vec2,
    pub size: Vec2,
    pub atlas_info: GlyphAtlasInfo,
    pub section_index: usize,
    pub byte_index: usize,
}

#[cfg(feature = "subpixel_glyph_atlas")]
struct GlyphPlacementAdjuster;

#[cfg(feature = "subpixel_glyph_atlas")]
impl GlyphPlacementAdjuster {
    #[inline(always)]
    pub fn new(_: &mut Glyph) -> Self {
        Self
    }

    #[inline(always)]
    pub fn position(&self, p: Vec2) -> Vec2 {
        p
    }
}

#[cfg(not(feature = "subpixel_glyph_atlas"))]
struct GlyphPlacementAdjuster(f32);

#[cfg(not(feature = "subpixel_glyph_atlas"))]
impl GlyphPlacementAdjuster {
    #[inline(always)]
    pub fn new(glyph: &mut Glyph) -> Self {
        let v = glyph.position.x.round();
        glyph.position.x = 0.;
        glyph.position.y = glyph.position.y.ceil();
        Self(v)
    }

    #[inline(always)]
    pub fn position(&self, v: Vec2) -> Vec2 {
        Vec2::new(self.0, 0.) + v
    }
}