slint/internal/backends/mcu/fonts.rs

// Copyright © SixtyFPS GmbH <info@slint-ui.com>
// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial

use alloc::vec::Vec;
use core::cell::RefCell;

#[cfg(all(not(feature = "std"), feature = "unsafe_single_core"))]
use i_slint_core::thread_local_ as thread_local;

use crate::{LogicalLength, LogicalSize, PhysicalLength, PhysicalSize, ScaleFactor};
use euclid::num::Zero;
use i_slint_core::{
    graphics::{BitmapFont, BitmapGlyph, BitmapGlyphs, FontRequest},
    slice::Slice,
};

thread_local! {
    static FONTS: RefCell<Vec<&'static BitmapFont>> = RefCell::default()
}

#[derive(Copy, Clone)]
pub struct Glyph(&'static BitmapGlyph);

impl Glyph {
    pub fn x(&self) -> PhysicalLength {
        PhysicalLength::new(self.0.x)
    }
    pub fn y(&self) -> PhysicalLength {
        PhysicalLength::new(self.0.y)
    }
    pub fn width(&self) -> PhysicalLength {
        PhysicalLength::new(self.0.width)
    }
    pub fn height(&self) -> PhysicalLength {
        PhysicalLength::new(self.0.height)
    }
    pub fn size(&self) -> PhysicalSize {
        PhysicalSize::from_lengths(self.width(), self.height())
    }
    pub fn x_advance(&self) -> PhysicalLength {
        PhysicalLength::new(self.0.x_advance)
    }
    pub fn data(&self) -> &Slice<'static, u8> {
        &self.0.data
    }
}

pub trait FontMetrics {
    fn ascent(&self, font: &BitmapFont) -> PhysicalLength;
    fn height(&self, font: &BitmapFont) -> PhysicalLength;
    fn pixel_size(&self) -> PhysicalLength;
}

impl FontMetrics for BitmapGlyphs {
    fn ascent(&self, font: &BitmapFont) -> PhysicalLength {
        (PhysicalLength::new(self.pixel_size).cast() * font.ascent / font.units_per_em).cast()
    }
    fn height(&self, font: &BitmapFont) -> PhysicalLength {
        // The descent is negative (relative to the baseline)
        (PhysicalLength::new(self.pixel_size).cast() * (font.ascent - font.descent)
            / font.units_per_em)
            .cast()
    }
    fn pixel_size(&self) -> PhysicalLength {
        PhysicalLength::new(self.pixel_size)
    }
}

pub const DEFAULT_FONT_SIZE: f32 = 12.0;

pub fn match_font(
    request: &FontRequest,
    scale_factor: ScaleFactor,
) -> (&'static BitmapFont, &'static BitmapGlyphs) {
    let font = FONTS.with(|fonts| {
        let fonts = fonts.borrow();
        let fallback_font =
            *fonts.first().expect("internal error: cannot render text without fonts");

        request.family.as_ref().map_or(fallback_font, |requested_family| {
            fonts
                .iter()
                .find(|bitmap_font| {
                    core::str::from_utf8(bitmap_font.family_name.as_slice()).unwrap()
                        == requested_family.as_str()
                })
                .unwrap_or(&fallback_font)
        })
    });

    let requested_pixel_size: PhysicalLength =
        (LogicalLength::new(request.pixel_size.unwrap_or(DEFAULT_FONT_SIZE)) * scale_factor).cast();

    let nearest_pixel_size = font
        .glyphs
        .partition_point(|glyphs| glyphs.pixel_size() <= requested_pixel_size)
        .saturating_sub(1);

    let matching_glyphs = &font.glyphs[nearest_pixel_size];

    (font, matching_glyphs)
}

pub fn register_bitmap_font(font_data: &'static BitmapFont) {
    FONTS.with(|fonts| fonts.borrow_mut().push(font_data))
}

pub fn glyphs_for_text<'a>(
    font: &'static BitmapFont,
    glyphs: &'static BitmapGlyphs,
    text: &'a str,
) -> impl Iterator<Item = (PhysicalLength, Glyph)> + 'a {
    let mut x: PhysicalLength = PhysicalLength::zero();
    text.chars().filter_map(move |char| {
        if let Some(glyph_index) = font
            .character_map
            .binary_search_by_key(&char, |char_map_entry| char_map_entry.code_point)
            .ok()
            .map(|char_map_index| font.character_map[char_map_index].glyph_index)
        {
            let glyph = Glyph(&glyphs.glyph_data[glyph_index as usize]);
            let glyph_x = x;
            x += glyph.x_advance();
            Some((glyph_x, glyph))
        } else {
            x += glyphs.pixel_size();
            None
        }
    })
}

pub fn text_size(
    font_request: FontRequest,
    text: &str,
    _max_width: Option<f32>,
    scale_factor: ScaleFactor,
) -> LogicalSize {
    let (font, glyphs) = match_font(&font_request, scale_factor);

    let width = glyphs_for_text(font, glyphs, text)
        .last()
        .map_or(PhysicalLength::zero(), |(last_x, last_glyph)| last_x + last_glyph.x_advance());

    PhysicalSize::from_lengths(width, glyphs.height(font)).cast() / scale_factor
}