fonts/platform/freetype/

font.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

use std::ffi::CString;
use std::fs::File;

use app_units::Au;
use euclid::default::{Point2D, Rect, Size2D};
use fonts_traits::{FontIdentifier, FontTemplateDescriptor, LocalFontIdentifier};
use freetype_sys::{
    FT_F26Dot6, FT_Get_Char_Index, FT_Get_Kerning, FT_GlyphSlot, FT_KERNING_DEFAULT,
    FT_LOAD_DEFAULT, FT_LOAD_NO_HINTING, FT_Load_Glyph, FT_Size_Metrics, FT_SizeRec, FT_UInt,
    FT_ULong, FT_Vector,
};
use log::debug;
use memmap2::Mmap;
use parking_lot::ReentrantMutex;
use read_fonts::types::Tag;
use read_fonts::{FontRef, ReadError, TableProvider};
use servo_arc::Arc;
use skrifa::attribute::Weight;
use style::Zero;
use webrender_api::{FontInstanceFlags, FontVariation};

use super::library_handle::FreeTypeLibraryHandle;
use crate::FontData;
use crate::font::{FontMetrics, FontTableMethods, FractionalPixel, PlatformFontMethods};
use crate::glyph::GlyphId;
use crate::platform::freetype::freetype_face::FreeTypeFace;

const SEMI_BOLD_U16: u16 = Weight::SEMI_BOLD.value() as u16;

/// Convert FreeType-style 26.6 fixed point to an [`f64`].
fn fixed_26_dot_6_to_float(fixed: FT_F26Dot6) -> f64 {
    fixed as f64 / 64.0
}

#[derive(Debug)]
pub struct FontTable {
    data: FreeTypeFaceTableProviderData,
    tag: Tag,
}

impl FontTableMethods for FontTable {
    fn buffer(&self) -> &[u8] {
        let font_ref = self.data.font_ref().expect("Font checked before creating");
        let table_data = font_ref
            .table_data(self.tag)
            .expect("Table existence checked before creating");
        table_data.as_bytes()
    }
}

#[derive(Debug)]
#[allow(unused)]
pub struct PlatformFont {
    face: ReentrantMutex<FreeTypeFace>,
    requested_face_size: Au,
    actual_face_size: Au,
    variations: Vec<FontVariation>,
    synthetic_bold: bool,

    /// A member that allows using `skrifa` to read values from this font.
    table_provider_data: FreeTypeFaceTableProviderData,
}

impl PlatformFontMethods for PlatformFont {
    fn new_from_data(
        _font_identifier: FontIdentifier,
        font_data: &FontData,
        requested_size: Option<Au>,
        variations: &[FontVariation],
        synthetic_bold: bool,
    ) -> Result<PlatformFont, &'static str> {
        let library = FreeTypeLibraryHandle::get().lock();
        let data: &[u8] = font_data.as_ref();
        let face = FreeTypeFace::new_from_memory(&library, data)?;

        let normalized_variations = face.set_variations_for_font(variations, &library)?;

        let (requested_face_size, actual_face_size) = match requested_size {
            Some(requested_size) => (requested_size, face.set_size(requested_size)?),
            None => (Au::zero(), Au::zero()),
        };

        let table_provider_data = FreeTypeFaceTableProviderData::Web(font_data.clone());

        let synthetic_bold = table_provider_data.should_apply_synthetic_bold(synthetic_bold);

        Ok(PlatformFont {
            face: ReentrantMutex::new(face),
            requested_face_size,
            actual_face_size,
            table_provider_data,
            variations: normalized_variations,
            synthetic_bold,
        })
    }

    fn new_from_local_font_identifier(
        font_identifier: LocalFontIdentifier,
        requested_size: Option<Au>,
        variations: &[FontVariation],
        synthetic_bold: bool,
    ) -> Result<PlatformFont, &'static str> {
        let library = FreeTypeLibraryHandle::get().lock();
        let filename = CString::new(&*font_identifier.path).expect("filename contains NUL byte!");

        let face = FreeTypeFace::new_from_file(
            &library,
            &filename,
            font_identifier.face_index_for_freetype(),
        )?;

        let normalized_variations = face.set_variations_for_font(variations, &library)?;

        let (requested_face_size, actual_face_size) = match requested_size {
            Some(requested_size) => (requested_size, face.set_size(requested_size)?),
            None => (Au::zero(), Au::zero()),
        };

        let Ok(memory_mapped_font_data) =
            File::open(&*font_identifier.path).and_then(|file| unsafe { Mmap::map(&file) })
        else {
            return Err("Could not memory map");
        };

        let table_provider_data = FreeTypeFaceTableProviderData::Local(
            Arc::new(memory_mapped_font_data),
            font_identifier.index(),
        );

        let synthetic_bold = table_provider_data.should_apply_synthetic_bold(synthetic_bold);

        Ok(PlatformFont {
            face: ReentrantMutex::new(face),
            requested_face_size,
            actual_face_size,
            table_provider_data,
            variations: normalized_variations,
            synthetic_bold,
        })
    }

    fn descriptor(&self) -> FontTemplateDescriptor {
        let Ok(font_ref) = self.table_provider_data.font_ref() else {
            return FontTemplateDescriptor::default();
        };
        let Ok(os2) = font_ref.os2() else {
            return FontTemplateDescriptor::default();
        };
        Self::descriptor_from_os2_table(&os2)
    }

    fn glyph_index(&self, codepoint: char) -> Option<GlyphId> {
        let face = self.face.lock();

        unsafe {
            let idx = FT_Get_Char_Index(face.as_ptr(), codepoint as FT_ULong);
            if idx != 0 as FT_UInt {
                Some(idx as GlyphId)
            } else {
                debug!(
                    "Invalid codepoint: U+{:04X} ('{}')",
                    codepoint as u32, codepoint
                );
                None
            }
        }
    }

    fn glyph_h_kerning(&self, first_glyph: GlyphId, second_glyph: GlyphId) -> FractionalPixel {
        let face = self.face.lock();

        let mut delta = FT_Vector { x: 0, y: 0 };
        unsafe {
            FT_Get_Kerning(
                face.as_ptr(),
                first_glyph,
                second_glyph,
                FT_KERNING_DEFAULT,
                &mut delta,
            );
        }
        fixed_26_dot_6_to_float(delta.x) * self.unscalable_font_metrics_scale()
    }

    fn glyph_h_advance(&self, glyph: GlyphId) -> Option<FractionalPixel> {
        let face = self.face.lock();

        let load_flags = face.glyph_load_flags();
        let result = unsafe { FT_Load_Glyph(face.as_ptr(), glyph as FT_UInt, load_flags) };
        if 0 != result {
            debug!("Unable to load glyph {}. reason: {:?}", glyph, result);
            return None;
        }

        let void_glyph = face.as_ref().glyph;
        let slot: FT_GlyphSlot = void_glyph;
        assert!(!slot.is_null());

        if self.synthetic_bold {
            mozilla_glyphslot_embolden_less(slot);
        }

        let advance = unsafe { (*slot).metrics.horiAdvance };
        Some(fixed_26_dot_6_to_float(advance) * self.unscalable_font_metrics_scale())
    }

    fn metrics(&self) -> FontMetrics {
        let face = self.face.lock();
        let font_ref = self.table_provider_data.font_ref();

        // face.size is a *c_void in the bindings, presumably to avoid recursive structural types
        let freetype_size: &FT_SizeRec = unsafe { &*face.as_ref().size };
        let freetype_metrics: &FT_Size_Metrics = &(freetype_size).metrics;

        let mut max_advance;
        let mut max_ascent;
        let mut max_descent;
        let mut line_height;
        let mut y_scale = 0.0;
        let mut em_height;
        if face.scalable() {
            // Prefer FT_Size_Metrics::y_scale to y_ppem as y_ppem does not have subpixel accuracy.
            //
            // FT_Size_Metrics::y_scale is in 16.16 fixed point format.  Its (fractional) value is a
            // factor that converts vertical metrics from design units to units of 1/64 pixels, so
            // that the result may be interpreted as pixels in 26.6 fixed point format.
            //
            // This converts the value to a float without losing precision.
            y_scale = freetype_metrics.y_scale as f64 / 65535.0 / 64.0;

            max_advance = (face.as_ref().max_advance_width as f64) * y_scale;
            max_ascent = (face.as_ref().ascender as f64) * y_scale;
            max_descent = -(face.as_ref().descender as f64) * y_scale;
            line_height = (face.as_ref().height as f64) * y_scale;
            em_height = (face.as_ref().units_per_EM as f64) * y_scale;
        } else {
            max_advance = fixed_26_dot_6_to_float(freetype_metrics.max_advance);
            max_ascent = fixed_26_dot_6_to_float(freetype_metrics.ascender);
            max_descent = -fixed_26_dot_6_to_float(freetype_metrics.descender);
            line_height = fixed_26_dot_6_to_float(freetype_metrics.height);

            em_height = freetype_metrics.y_ppem as f64;
            // FT_Face doc says units_per_EM and a bunch of following fields are "only relevant to
            // scalable outlines". If it's an sfnt, we can get units_per_EM from the 'head' table
            // instead; otherwise, we don't have a unitsPerEm value so we can't compute y_scale and
            // x_scale.
            if let Ok(head) = font_ref.clone().and_then(|font_ref| font_ref.head()) {
                // Bug 1267909 - Even if the font is not explicitly scalable, if the face has color
                // bitmaps, it should be treated as scalable and scaled to the desired size. Metrics
                // based on y_ppem need to be rescaled for the adjusted size.
                if face.color() {
                    em_height = self.requested_face_size.to_f64_px();
                    let adjust_scale = em_height / (freetype_metrics.y_ppem as f64);
                    max_advance *= adjust_scale;
                    max_descent *= adjust_scale;
                    max_ascent *= adjust_scale;
                    line_height *= adjust_scale;
                }
                y_scale = em_height / head.units_per_em() as f64;
            }
        }

        // 'leading' is supposed to be the vertical distance between two baselines,
        // reflected by the height attribute in freetype. On OS X (w/ CTFont),
        // leading represents the distance between the bottom of a line descent to
        // the top of the next line's ascent or: (line_height - ascent - descent),
        // see http://stackoverflow.com/a/5635981 for CTFont implementation.
        // Convert using a formula similar to what CTFont returns for consistency.
        let leading = line_height - (max_ascent + max_descent);

        let underline_size = face.as_ref().underline_thickness as f64 * y_scale;
        let underline_offset = face.as_ref().underline_position as f64 * y_scale + 0.5;

        // The default values for strikeout size and offset. Use OpenType spec's suggested position
        // for Roman font as the default for offset.
        let mut strikeout_size = underline_size;
        let mut strikeout_offset = em_height * 409.0 / 2048.0 + 0.5 * strikeout_size;

        // CSS 2.1, section 4.3.2 Lengths: "In the cases where it is
        // impossible or impractical to determine the x-height, a value of
        // 0.5em should be used."
        let mut x_height = 0.5 * em_height;
        let mut average_advance = 0.0;

        if let Ok(os2) = font_ref.and_then(|font_ref| font_ref.os2()) {
            let y_strikeout_size = os2.y_strikeout_size();
            let y_strikeout_position = os2.y_strikeout_position();
            if !y_strikeout_size.is_zero() && !y_strikeout_position.is_zero() {
                strikeout_size = y_strikeout_size as f64 * y_scale;
                strikeout_offset = y_strikeout_position as f64 * y_scale;
            }

            let sx_height = os2.sx_height().unwrap_or(0);
            if !sx_height.is_zero() {
                x_height = sx_height as f64 * y_scale;
            }

            let x_average_char_width = os2.x_avg_char_width();
            if !x_average_char_width.is_zero() {
                average_advance = x_average_char_width as f64 * y_scale;
            }
        }

        if average_advance.is_zero() {
            average_advance = self
                .glyph_index('0')
                .and_then(|idx| self.glyph_h_advance(idx))
                .map_or(max_advance, |advance| advance * y_scale);
        }

        let zero_horizontal_advance = self
            .glyph_index('0')
            .and_then(|idx| self.glyph_h_advance(idx))
            .map(Au::from_f64_px);
        let ic_horizontal_advance = self
            .glyph_index('\u{6C34}')
            .and_then(|idx| self.glyph_h_advance(idx))
            .map(Au::from_f64_px);
        let space_advance = self
            .glyph_index(' ')
            .and_then(|idx| self.glyph_h_advance(idx))
            .unwrap_or(average_advance);

        FontMetrics {
            underline_size: Au::from_f64_px(underline_size),
            underline_offset: Au::from_f64_px(underline_offset),
            strikeout_size: Au::from_f64_px(strikeout_size),
            strikeout_offset: Au::from_f64_px(strikeout_offset),
            leading: Au::from_f64_px(leading),
            x_height: Au::from_f64_px(x_height),
            em_size: Au::from_f64_px(em_height),
            ascent: Au::from_f64_px(max_ascent),
            descent: Au::from_f64_px(max_descent),
            max_advance: Au::from_f64_px(max_advance),
            average_advance: Au::from_f64_px(average_advance),
            line_gap: Au::from_f64_px(line_height),
            zero_horizontal_advance,
            ic_horizontal_advance,
            space_advance: Au::from_f64_px(space_advance),
        }
    }

    fn table_for_tag(&self, tag: Tag) -> Option<FontTable> {
        let font_ref = self.table_provider_data.font_ref().ok()?;
        let _table_data = font_ref.table_data(tag)?;
        Some(FontTable {
            data: self.table_provider_data.clone(),
            tag,
        })
    }

    fn typographic_bounds(&self, glyph_id: GlyphId) -> Rect<f32> {
        let face = self.face.lock();

        let load_flags = FT_LOAD_DEFAULT | FT_LOAD_NO_HINTING;
        let result = unsafe { FT_Load_Glyph(face.as_ptr(), glyph_id as FT_UInt, load_flags) };
        if 0 != result {
            debug!("Unable to load glyph {}. reason: {:?}", glyph_id, result);
            return Rect::default();
        }

        let metrics = unsafe { &(*face.as_ref().glyph).metrics };

        Rect::new(
            Point2D::new(
                metrics.horiBearingX as f32,
                (metrics.horiBearingY - metrics.height) as f32,
            ),
            Size2D::new(metrics.width as f32, metrics.height as f32),
        ) * (1. / 64.)
    }

    fn webrender_font_instance_flags(&self) -> FontInstanceFlags {
        // On other platforms, we only pass this when we know that we are loading a font with
        // color characters, but not passing this flag simply *prevents* WebRender from
        // loading bitmaps. There's no harm to always passing it.
        let mut flags = FontInstanceFlags::EMBEDDED_BITMAPS;

        // TODO: Add support for synthetic italics.
        // <https://github.com/servo/servo/issues/39637>
        if self.synthetic_bold {
            flags |= FontInstanceFlags::SYNTHETIC_BOLD;
        }

        flags
    }

    fn variations(&self) -> &[FontVariation] {
        &self.variations
    }
}

impl PlatformFont {
    /// Find the scale to use for metrics of unscalable fonts. Unscalable fonts, those using bitmap
    /// glyphs, are scaled after glyph rasterization. In order for metrics to match the final scaled
    /// font, we need to scale them based on the final size and the actual font size.
    fn unscalable_font_metrics_scale(&self) -> f64 {
        self.requested_face_size.to_f64_px() / self.actual_face_size.to_f64_px()
    }
}

#[derive(Clone)]
enum FreeTypeFaceTableProviderData {
    Web(FontData),
    Local(Arc<Mmap>, u32),
}

impl FreeTypeFaceTableProviderData {
    fn font_ref(&self) -> Result<FontRef<'_>, ReadError> {
        match self {
            Self::Web(ipc_shared_memory) => FontRef::new(ipc_shared_memory.as_ref()),
            Self::Local(mmap, index) => FontRef::from_index(mmap, *index),
        }
    }

    fn should_apply_synthetic_bold(&self, synthetic_bold: bool) -> bool {
        // Ensures that a font face is not emboldened if it's a variable font or
        // if it's already bold.
        let face_is_bold = self
            .font_ref()
            .and_then(|font_ref| font_ref.os2())
            .is_ok_and(|table| table.us_weight_class() >= SEMI_BOLD_U16);
        let is_variable_font = self
            .font_ref()
            .and_then(|font_ref| font_ref.fvar())
            .is_ok_and(|table| table.axis_count() > 0);
        !face_is_bold && !is_variable_font && synthetic_bold
    }
}

impl std::fmt::Debug for FreeTypeFaceTableProviderData {
    fn fmt(&self, _: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        Ok(())
    }
}

// This is copied from the webrender glyph rasterizer
// https://github.com/servo/webrender/blob/c4bd5b47d8f5cd684334b445e67a1f945d106848/wr_glyph_rasterizer/src/platform/unix/font.rs#L115
//
// Custom version of FT_GlyphSlot_Embolden to be less aggressive with outline
// fonts than the default implementation in FreeType.
fn mozilla_glyphslot_embolden_less(slot: FT_GlyphSlot) {
    use freetype_sys::{
        FT_GLYPH_FORMAT_OUTLINE, FT_GlyphSlot_Embolden, FT_Long, FT_MulFix, FT_Outline_Embolden,
    };

    if slot.is_null() {
        return;
    }

    let slot_ = unsafe { &mut *slot };
    let format = slot_.format;
    if format != FT_GLYPH_FORMAT_OUTLINE {
        // For non-outline glyphs, just fall back to FreeType's function.
        unsafe { FT_GlyphSlot_Embolden(slot) };
        return;
    }

    let face_ = unsafe { &*slot_.face };

    // FT_GlyphSlot_Embolden uses a divisor of 24 here; we'll be only half as
    // bold.
    let size_ = unsafe { &*face_.size };
    let strength = unsafe { FT_MulFix(face_.units_per_EM as FT_Long, size_.metrics.y_scale) / 48 };
    unsafe { FT_Outline_Embolden(&raw mut slot_.outline, strength) };

    // Adjust metrics to suit the fattened glyph.
    if slot_.advance.x != 0 {
        slot_.advance.x += strength;
    }
    if slot_.advance.y != 0 {
        slot_.advance.y += strength;
    }
    slot_.metrics.width += strength;
    slot_.metrics.height += strength;
    slot_.metrics.horiAdvance += strength;
    slot_.metrics.vertAdvance += strength;
    slot_.metrics.horiBearingY += strength;
}