fonts: Use fontations to read the OS/2 table of DirectWrite fonts (#38851)

Instead of copying the font table data in memory and parsing it with the
`truetype` crate, use a non-copying API from DirectWrite to implement a
`fontations` `TableProvider`. This has two benefits:

- We remove the dependency on the `truetype` crate finally.
- We do not have to make an in-memory copy of the table data when
  parsing the table.

The hope is that the `TableProvider` will be more generally useful in
the future.

Testing: There are no automated tests for Windows, but I manually
verified
that the data retrived via `fontations` matched that retrived by
`truetype`.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

Cargo.lock

@@ -2708,11 +2708,11 @@ dependencies = [
  "stylo",
  "stylo_atoms",
  "tracing",
- "truetype",
  "unicode-properties",
  "unicode-script",
  "url",
  "webrender_api",
+ "winapi",
  "xml-rs",
  "yeslogic-fontconfig-sys",
 ]
@@ -8988,15 +8988,6 @@ version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ce607aae8ab0ab3abf3a2723a9ab6f09bb8639ed83fdd888d857b8e556c868d8"
 
-[[package]]
-name = "truetype"
-version = "0.47.10"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "05ce9543b570c6e8a392274b67e1001816bce953aa89724e52a4639db02a10e0"
-dependencies = [
- "typeface",
-]
-
 [[package]]
 name = "try-lock"
 version = "0.2.5"
@@ -9037,12 +9028,6 @@ version = "2.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6af6ae20167a9ece4bcb41af5b80f8a1f1df981f6391189ce00fd257af04126a"
 
-[[package]]
-name = "typeface"
-version = "0.4.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "191ea6762cbcd705fbed8f58573fd6c654453ff3da60adb293d9f255bc92af8e"
-
 [[package]]
 name = "typeid"
 version = "1.0.3"

components/fonts/Cargo.toml

@@ -74,7 +74,7 @@ xml-rs = "0.8"
 
 [target.'cfg(target_os = "windows")'.dependencies]
 dwrote = "0.11.4"
-truetype = { version = "0.47.3", features = ["ignore-invalid-language-ids"] }
+winapi = { workspace = true }
 
 [lints.rust]
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(ohos_mock)'] }

components/fonts/font.rs

@@ -18,6 +18,7 @@ use euclid::num::Zero;
 use log::debug;
 use malloc_size_of_derive::MallocSizeOf;
 use parking_lot::RwLock;
+use read_fonts::tables::os2::{Os2, SelectionFlags};
 use serde::{Deserialize, Serialize};
 use smallvec::SmallVec;
 use style::computed_values::font_variant_caps;
@@ -119,6 +120,29 @@ pub trait PlatformFontMethods: Sized {
 
     /// Return all the variation values that the font was instantiated with.
     fn variations(&self) -> &[FontVariation];
+
+    fn descriptor_from_os2_table(os2: &Os2) -> FontTemplateDescriptor {
+        let mut style = FontStyle::NORMAL;
+        if os2.fs_selection().contains(SelectionFlags::ITALIC) {
+            style = FontStyle::ITALIC;
+        }
+
+        let weight = FontWeight::from_float(os2.us_weight_class() as f32);
+        let stretch = match os2.us_width_class() {
+            1 => FontStretch::ULTRA_CONDENSED,
+            2 => FontStretch::EXTRA_CONDENSED,
+            3 => FontStretch::CONDENSED,
+            4 => FontStretch::SEMI_CONDENSED,
+            5 => FontStretch::NORMAL,
+            6 => FontStretch::SEMI_EXPANDED,
+            7 => FontStretch::EXPANDED,
+            8 => FontStretch::EXTRA_EXPANDED,
+            9 => FontStretch::ULTRA_EXPANDED,
+            _ => FontStretch::NORMAL,
+        };
+
+        FontTemplateDescriptor::new(weight, stretch, style)
+    }
 }
 
 // Used to abstract over the shaper's choice of fixed int representation.

components/fonts/platform/freetype/font.rs

@@ -15,14 +15,10 @@ use freetype_sys::{
 use log::debug;
 use memmap2::Mmap;
 use parking_lot::ReentrantMutex;
-use read_fonts::tables::os2::SelectionFlags;
 use read_fonts::types::Tag;
 use read_fonts::{FontRef, ReadError, TableProvider};
 use servo_arc::Arc;
 use style::Zero;
-use style::computed_values::font_stretch::T as FontStretch;
-use style::computed_values::font_weight::T as FontWeight;
-use style::values::computed::font::FontStyle;
 use webrender_api::{FontInstanceFlags, FontVariation};
 
 use super::LocalFontIdentifier;
@@ -135,31 +131,10 @@ impl PlatformFontMethods for PlatformFont {
         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)
-        let mut style = FontStyle::NORMAL;
-        if os2.fs_selection().contains(SelectionFlags::ITALIC) {
-            style = FontStyle::ITALIC;
-        }
-
-        let weight = FontWeight::from_float(os2.us_weight_class() as f32);
-        let stretch = match os2.us_width_class() {
-            1 => FontStretch::ULTRA_CONDENSED,
-            2 => FontStretch::EXTRA_CONDENSED,
-            3 => FontStretch::CONDENSED,
-            4 => FontStretch::SEMI_CONDENSED,
-            5 => FontStretch::NORMAL,
-            6 => FontStretch::SEMI_EXPANDED,
-            7 => FontStretch::EXPANDED,
-            8 => FontStretch::EXTRA_EXPANDED,
-            9 => FontStretch::ULTRA_EXPANDED,
-            _ => FontStretch::NORMAL,
-        };
-
-        FontTemplateDescriptor::new(weight, stretch, style)
     }
 
     fn glyph_index(&self, codepoint: char) -> Option<GlyphId> {

components/fonts/platform/windows/font.rs

@@ -6,8 +6,9 @@
 // information for an approach that we'll likely need to take when the
 // renderer moves to a sandboxed process.
 
+use std::cell::RefCell;
+use std::ffi::c_void;
 use std::fmt;
-use std::io::Cursor;
 use std::ops::Deref;
 use std::sync::Arc;
 
@@ -16,19 +17,17 @@ use dwrote::{
     DWRITE_FONT_AXIS_VALUE, DWRITE_FONT_SIMULATIONS_NONE, FontCollection, FontFace, FontFile,
 };
 use euclid::default::{Point2D, Rect, Size2D};
-use log::{debug, warn};
+use log::debug;
+use read_fonts::TableProvider;
+use skrifa::Tag;
 use style::Zero;
-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, FontVariation};
+use winapi::shared::minwindef::{BOOL, FALSE};
 
 use super::font_list::LocalFontIdentifier;
 use crate::{
     FontData, FontIdentifier, FontMetrics, FontTableMethods, FontTableTag, FontTemplateDescriptor,
-    FractionalPixel, GlyphId, PlatformFontMethods, ot_tag,
+    FractionalPixel, GlyphId, PlatformFontMethods,
 };
 
 // 1em = 12pt = 16px, assuming 72 points per inch and 96 px per inch
@@ -190,71 +189,11 @@ impl PlatformFontMethods for PlatformFont {
     }
 
     fn descriptor(&self) -> FontTemplateDescriptor {
-        // We need the font (DWriteFont) in order to be able to query things like
+        DirectWriteTableProvider::new(self)
-        // the family name, face name, weight, etc.  On Windows 10, the
+            .os2()
-        // DWriteFontFace3 interface provides this on the FontFace, but that's only
+            .as_ref()
-        // available on Win10+.
+            .map(Self::descriptor_from_os2_table)
-        //
+            .unwrap_or_default()
-        // 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 width_val.clamp(1, 9) {
-            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> {
@@ -374,3 +313,71 @@ impl PlatformFontMethods for PlatformFont {
         &self.variations
     }
 }
+
+/// A wrapper struct around [`PlatformFont`] which is responsible for
+/// implementing [`TableProvider`] and cleaning up any font table contexts from
+/// DirectWrite when the struct is dropped.
+struct DirectWriteTableProvider<'platform_font> {
+    platform_font: &'platform_font PlatformFont,
+    contexts: RefCell<Vec<*mut c_void>>,
+}
+
+impl<'platform_font> DirectWriteTableProvider<'platform_font> {
+    fn new(platform_font: &'platform_font PlatformFont) -> Self {
+        Self {
+            platform_font,
+            contexts: Default::default(),
+        }
+    }
+}
+
+impl Drop for DirectWriteTableProvider<'_> {
+    fn drop(&mut self) {
+        let direct_write_face = unsafe { self.platform_font.face.as_ptr() };
+        assert!(!direct_write_face.is_null());
+
+        let direct_write_face = unsafe { &*direct_write_face };
+        for context in self.contexts.borrow_mut().drain(..) {
+            unsafe { direct_write_face.ReleaseFontTable(context) };
+        }
+    }
+}
+
+impl<'platform_font> TableProvider<'platform_font> for DirectWriteTableProvider<'platform_font> {
+    fn data_for_tag(&self, tag: Tag) -> Option<read_fonts::FontData<'platform_font>> {
+        let direct_write_face = unsafe { self.platform_font.face.as_ptr() };
+        if direct_write_face.is_null() {
+            return None;
+        }
+
+        let direct_write_face = unsafe { &*direct_write_face };
+        let direct_write_tag = u32::from_be_bytes(tag.to_be_bytes()).swap_bytes();
+        let mut table_data_ptr: *const u8 = std::ptr::null_mut();
+        let mut table_size: u32 = 0;
+        let mut table_context: *mut c_void = std::ptr::null_mut();
+        let mut exists: BOOL = FALSE;
+
+        let hr = unsafe {
+            direct_write_face.TryGetFontTable(
+                direct_write_tag,
+                &mut table_data_ptr as *mut *const _ as *mut *const c_void,
+                &mut table_size,
+                &mut table_context,
+                &mut exists,
+            )
+        };
+
+        if hr != 0 || exists == 0 {
+            return None;
+        }
+
+        self.contexts.borrow_mut().push(table_context);
+
+        if table_data_ptr.is_null() || table_size == 0 {
+            return None;
+        }
+
+        let bytes = unsafe { std::slice::from_raw_parts(table_data_ptr, table_size as usize) };
+        Some(read_fonts::FontData::new(bytes))
+    }
+}