Rename gfx to fonts (#32556)

This crate only takes care of fonts now as graphics related things are
split into other crates. In addition, this exposes data structures at
the top of the crate, hiding the implementation details and making it
simpler to import them.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Mukilan Thiyagarajan <mukilan@igalia.com>

components/fonts/platform/windows/font.rs

@@ -0,0 +1,276 @@
+/* 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/. */
+
+// NOTE: https://www.chromium.org/directwrite-font-proxy has useful
+// information for an approach that we'll likely need to take when the
+// renderer moves to a sandboxed process.
+
+use std::cmp::{max, min};
+use std::fmt;
+use std::io::Cursor;
+use std::ops::Deref;
+use std::sync::Arc;
+
+use app_units::Au;
+use dwrote::{FontFace, FontFile};
+use log::{debug, warn};
+use style::computed_values::font_stretch::T as StyleFontStretch;
+use style::computed_values::font_weight::T as StyleFontWeight;
+use style::values::computed::font::FontStyle as StyleFontStyle;
+use truetype::tables::WindowsMetrics;
+use truetype::value::Read;
+use webrender_api::FontInstanceFlags;
+
+use crate::{
+    ot_tag, FontIdentifier, FontMetrics, FontTableMethods, FontTableTag, FontTemplateDescriptor,
+    FractionalPixel, GlyphId, PlatformFontMethods,
+};
+
+// 1em = 12pt = 16px, assuming 72 points per inch and 96 px per inch
+fn pt_to_px(pt: f64) -> f64 {
+    pt / 72. * 96.
+}
+fn em_to_px(em: f64) -> f64 {
+    em * 16.
+}
+fn au_from_em(em: f64) -> Au {
+    Au::from_f64_px(em_to_px(em))
+}
+fn au_from_pt(pt: f64) -> Au {
+    Au::from_f64_px(pt_to_px(pt))
+}
+
+pub struct FontTable {
+    data: Vec<u8>,
+}
+
+impl FontTable {
+    pub fn wrap(data: &[u8]) -> FontTable {
+        FontTable {
+            data: data.to_vec(),
+        }
+    }
+}
+
+impl FontTableMethods for FontTable {
+    fn buffer(&self) -> &[u8] {
+        &self.data
+    }
+}
+
+#[derive(Debug)]
+pub struct PlatformFont {
+    face: Nondebug<FontFace>,
+    /// A reference to this data used to create this [`PlatformFont`], ensuring the
+    /// data stays alive of the lifetime of this struct.
+    _data: Arc<Vec<u8>>,
+    em_size: f32,
+    du_to_px: f32,
+    scaled_du_to_px: f32,
+}
+
+// Based on information from the Skia codebase, it seems that DirectWrite APIs from
+// Windows 10 and beyond are thread safe.  If problems arise from this, we can protect the
+// platform font with a Mutex.
+// See https://source.chromium.org/chromium/chromium/src/+/main:third_party/skia/src/ports/SkScalerContext_win_dw.cpp;l=56;bpv=0;bpt=1.
+unsafe impl Sync for PlatformFont {}
+unsafe impl Send for PlatformFont {}
+
+struct Nondebug<T>(T);
+
+impl<T> fmt::Debug for Nondebug<T> {
+    fn fmt(&self, _f: &mut fmt::Formatter) -> fmt::Result {
+        Ok(())
+    }
+}
+
+impl<T> Deref for Nondebug<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        &self.0
+    }
+}
+
+impl PlatformFontMethods for PlatformFont {
+    fn new_from_data(
+        _font_identifier: FontIdentifier,
+        data: Arc<Vec<u8>>,
+        face_index: u32,
+        pt_size: Option<Au>,
+    ) -> Result<Self, &'static str> {
+        let font_file = FontFile::new_from_data(data.clone()).ok_or("Could not create FontFile")?;
+        let face = font_file
+            .create_face(face_index, dwrote::DWRITE_FONT_SIMULATIONS_NONE)
+            .map_err(|_| "Could not create FontFace")?;
+
+        let pt_size = pt_size.unwrap_or(au_from_pt(12.));
+        let du_per_em = face.metrics().metrics0().designUnitsPerEm as f32;
+
+        let em_size = pt_size.to_f32_px() / 16.;
+        let design_units_per_pixel = du_per_em / 16.;
+
+        let design_units_to_pixels = 1. / design_units_per_pixel;
+        let scaled_design_units_to_pixels = em_size / design_units_per_pixel;
+
+        Ok(PlatformFont {
+            face: Nondebug(face),
+            _data: data,
+            em_size,
+            du_to_px: design_units_to_pixels,
+            scaled_du_to_px: scaled_design_units_to_pixels,
+        })
+    }
+
+    fn descriptor(&self) -> FontTemplateDescriptor {
+        // We need the font (DWriteFont) in order to be able to query things like
+        // the family name, face name, weight, etc.  On Windows 10, the
+        // DWriteFontFace3 interface provides this on the FontFace, but that's only
+        // available on Win10+.
+        //
+        // Instead, we do the parsing work using the truetype crate for raw fonts.
+        // We're just extracting basic info, so this is sufficient for now.
+        //
+        // The `dwrote` APIs take SFNT table tags in a reversed byte order, which
+        // is why `u32::swap_bytes()` is called here.
+        let windows_metrics_bytes = self
+            .face
+            .get_font_table(u32::swap_bytes(ot_tag!('O', 'S', '/', '2')));
+        if windows_metrics_bytes.is_none() {
+            warn!("Could not find OS/2 table in font.");
+            return FontTemplateDescriptor::default();
+        }
+
+        let mut cursor = Cursor::new(windows_metrics_bytes.as_ref().unwrap());
+        let Ok(table) = WindowsMetrics::read(&mut cursor) else {
+            warn!("Could not read OS/2 table in font.");
+            return FontTemplateDescriptor::default();
+        };
+
+        let (weight_val, width_val, italic_bool) = match table {
+            WindowsMetrics::Version0(ref m) => {
+                (m.weight_class, m.width_class, m.selection_flags.0 & 1 == 1)
+            },
+            WindowsMetrics::Version1(ref m) => {
+                (m.weight_class, m.width_class, m.selection_flags.0 & 1 == 1)
+            },
+            WindowsMetrics::Version2(ref m) |
+            WindowsMetrics::Version3(ref m) |
+            WindowsMetrics::Version4(ref m) => {
+                (m.weight_class, m.width_class, m.selection_flags.0 & 1 == 1)
+            },
+            WindowsMetrics::Version5(ref m) => {
+                (m.weight_class, m.width_class, m.selection_flags.0 & 1 == 1)
+            },
+        };
+
+        let weight = StyleFontWeight::from_float(weight_val as f32);
+        let stretch = match min(9, max(1, width_val)) {
+            1 => StyleFontStretch::ULTRA_CONDENSED,
+            2 => StyleFontStretch::EXTRA_CONDENSED,
+            3 => StyleFontStretch::CONDENSED,
+            4 => StyleFontStretch::SEMI_CONDENSED,
+            5 => StyleFontStretch::NORMAL,
+            6 => StyleFontStretch::SEMI_EXPANDED,
+            7 => StyleFontStretch::EXPANDED,
+            8 => StyleFontStretch::EXTRA_EXPANDED,
+            9 => StyleFontStretch::ULTRA_CONDENSED,
+            _ => {
+                warn!("Unknown stretch size.");
+                StyleFontStretch::NORMAL
+            },
+        };
+
+        let style = if italic_bool {
+            StyleFontStyle::ITALIC
+        } else {
+            StyleFontStyle::NORMAL
+        };
+
+        FontTemplateDescriptor::new(weight, stretch, style)
+    }
+
+    fn glyph_index(&self, codepoint: char) -> Option<GlyphId> {
+        let glyph = self.face.get_glyph_indices(&[codepoint as u32])[0];
+        if glyph == 0 {
+            return None;
+        }
+        Some(glyph as GlyphId)
+    }
+
+    fn glyph_h_advance(&self, glyph: GlyphId) -> Option<FractionalPixel> {
+        if glyph == 0 {
+            return None;
+        }
+
+        let gm = self.face.get_design_glyph_metrics(&[glyph as u16], false)[0];
+        let f = (gm.advanceWidth as f32 * self.scaled_du_to_px) as FractionalPixel;
+
+        Some(f)
+    }
+
+    /// Can this font do basic horizontal LTR shaping without Harfbuzz?
+    fn can_do_fast_shaping(&self) -> bool {
+        // TODO copy CachedKernTable from the MacOS X implementation to
+        // somehwere global and use it here.  We could also implement the
+        // IDirectWriteFontFace1 interface and use the glyph kerning pair
+        // methods there.
+        false
+    }
+
+    fn glyph_h_kerning(&self, _: GlyphId, _: GlyphId) -> FractionalPixel {
+        0.0
+    }
+
+    fn metrics(&self) -> FontMetrics {
+        let dm = self.face.metrics().metrics0();
+
+        let au_from_du = |du| -> Au { Au::from_f32_px(du as f32 * self.du_to_px) };
+        let au_from_du_s = |du| -> Au { Au::from_f32_px(du as f32 * self.scaled_du_to_px) };
+
+        // anything that we calculate and don't just pull out of self.face.metrics
+        // is pulled out here for clarity
+        let leading = dm.ascent - dm.capHeight;
+
+        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 metrics = FontMetrics {
+            underline_size: au_from_du(dm.underlineThickness as i32),
+            underline_offset: au_from_du_s(dm.underlinePosition as i32),
+            strikeout_size: au_from_du(dm.strikethroughThickness as i32),
+            strikeout_offset: au_from_du_s(dm.strikethroughPosition as i32),
+            leading: au_from_du_s(leading as i32),
+            x_height: au_from_du_s(dm.xHeight as i32),
+            em_size: au_from_em(self.em_size as f64),
+            ascent: au_from_du_s(dm.ascent as i32),
+            descent: au_from_du_s(dm.descent as i32),
+            max_advance: au_from_pt(0.0),     // FIXME
+            average_advance: au_from_pt(0.0), // FIXME
+            line_gap: au_from_du_s((dm.ascent + dm.descent + dm.lineGap as u16) as i32),
+            zero_horizontal_advance,
+            ic_horizontal_advance,
+        };
+        debug!("Font metrics (@{} pt): {:?}", self.em_size * 12., metrics);
+        metrics
+    }
+
+    fn table_for_tag(&self, tag: FontTableTag) -> Option<FontTable> {
+        // dwrote (and presumably the Windows APIs) accept a reversed version of the table
+        // tag bytes, which means that `u32::swap_bytes` must be called here in order to
+        // use a byte order compatible with the rest of Servo.
+        self.face
+            .get_font_table(u32::swap_bytes(tag))
+            .map(|bytes| FontTable { data: bytes })
+    }
+
+    fn webrender_font_instance_flags(&self) -> FontInstanceFlags {
+        FontInstanceFlags::empty()
+    }
+}