tor-browser

font.rs (45646B)

---

/* 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 http://mozilla.org/MPL/2.0/. */

#![allow(non_camel_case_types)]

use api::{ColorU, GlyphDimensions, FontKey, FontRenderMode};
use api::{FontInstancePlatformOptions, FontLCDFilter, FontHinting};
use api::{FontInstanceFlags, FontTemplate, FontVariation, NativeFontHandle};
use freetype::freetype::{FT_BBox, FT_Outline_Translate, FT_Pixel_Mode, FT_Render_Mode};
use freetype::freetype::{FT_Done_Face, FT_Error, FT_Get_Char_Index, FT_Int32};
use freetype::freetype::{FT_Done_FreeType, FT_Library_SetLcdFilter, FT_Pos};
use freetype::freetype::{FT_F26Dot6, FT_Face, FT_Glyph_Format, FT_Long, FT_UInt};
use freetype::freetype::{FT_GlyphSlot, FT_LcdFilter, FT_New_Face, FT_New_Memory_Face};
use freetype::freetype::{FT_Init_FreeType, FT_Load_Glyph, FT_Render_Glyph};
use freetype::freetype::{FT_Library, FT_Outline_Get_CBox, FT_Set_Char_Size, FT_Select_Size};
use freetype::freetype::{FT_Fixed, FT_Matrix, FT_Set_Transform, FT_String, FT_ULong, FT_Vector};
use freetype::freetype::{FT_Err_Unimplemented_Feature, FT_MulFix, FT_Outline_Embolden};
use freetype::freetype::{FT_LOAD_COLOR, FT_LOAD_DEFAULT, FT_LOAD_FORCE_AUTOHINT};
use freetype::freetype::{FT_LOAD_IGNORE_GLOBAL_ADVANCE_WIDTH, FT_LOAD_NO_AUTOHINT};
use freetype::freetype::{FT_LOAD_NO_BITMAP, FT_LOAD_NO_HINTING};
use freetype::freetype::{FT_FACE_FLAG_SCALABLE, FT_FACE_FLAG_FIXED_SIZES};
use freetype::freetype::FT_FACE_FLAG_MULTIPLE_MASTERS;
use freetype::succeeded;
use crate::gamma_lut::{ColorLut, GammaLut};
use crate::rasterizer::{FontInstance, GlyphFormat, GlyphKey};
use crate::rasterizer::{GlyphRasterError, GlyphRasterResult, RasterizedGlyph};
use crate::types::FastHashMap;
#[cfg(any(not(target_os = "android"), feature = "dynamic_freetype"))]
use libc::{dlsym, RTLD_DEFAULT};
use libc::free;
use std::{cmp, mem, ptr, slice};
use std::cmp::max;
use std::ffi::CString;
use std::sync::{Arc, Condvar, Mutex, MutexGuard};

#[cfg(not(target_os = "android"))]
const FONT_GAMMA: f32 = 0.0;
#[cfg(target_os = "android")]
const FONT_GAMMA: f32 = 1.4;

lazy_static! {
   static ref GAMMA_LUT: GammaLut = GammaLut::new(0.0, FONT_GAMMA, FONT_GAMMA);
}

// These constants are not present in the freetype
// bindings due to bindgen not handling the way
// the macros are defined.
//const FT_LOAD_TARGET_NORMAL: FT_UInt = 0 << 16;
const FT_LOAD_TARGET_LIGHT: FT_UInt  = 1 << 16;
const FT_LOAD_TARGET_MONO: FT_UInt   = 2 << 16;
const FT_LOAD_TARGET_LCD: FT_UInt    = 3 << 16;
const FT_LOAD_TARGET_LCD_V: FT_UInt  = 4 << 16;

#[repr(C)]
struct FT_Var_Axis {
   pub name: *mut FT_String,
   pub minimum: FT_Fixed,
   pub def: FT_Fixed,
   pub maximum: FT_Fixed,
   pub tag: FT_ULong,
   pub strid: FT_UInt,
}

#[repr(C)]
struct FT_Var_Named_Style {
   pub coords: *mut FT_Fixed,
   pub strid: FT_UInt,
   pub psid: FT_UInt,
}

#[repr(C)]
struct FT_MM_Var {
   pub num_axis: FT_UInt,
   pub num_designs: FT_UInt,
   pub num_namedstyles: FT_UInt,
   pub axis: *mut FT_Var_Axis,
   pub namedstyle: *mut FT_Var_Named_Style,
}

#[inline]
pub fn unimplemented(error: FT_Error) -> bool {
   error == FT_Err_Unimplemented_Feature as FT_Error
}

// Use dlsym to check for symbols. If not available. just return an unimplemented error.
#[cfg(any(not(target_os = "android"), feature = "dynamic_freetype"))]
macro_rules! ft_dyn_fn {
   ($func_name:ident($($arg_name:ident:$arg_type:ty),*) -> FT_Error) => {
       #[allow(non_snake_case)]
       unsafe fn $func_name($($arg_name:$arg_type),*) -> FT_Error {
           extern "C" fn unimpl_func($(_:$arg_type),*) -> FT_Error {
               FT_Err_Unimplemented_Feature as FT_Error
           }
           lazy_static! {
               static ref FUNC: unsafe extern "C" fn($($arg_type),*) -> FT_Error = {
                   unsafe {
                       let cname = CString::new(stringify!($func_name)).unwrap();
                       let ptr = dlsym(RTLD_DEFAULT, cname.as_ptr());
                       if !ptr.is_null() { mem::transmute(ptr) } else { unimpl_func }
                   }
               };
           }
           (*FUNC)($($arg_name),*)
       }
   }
}

// On Android, just statically link in the symbols...
#[cfg(all(target_os = "android", not(feature = "dynamic_freetype")))]
macro_rules! ft_dyn_fn {
   ($($proto:tt)+) => { extern "C" { fn $($proto)+; } }
}

ft_dyn_fn!(FT_Get_MM_Var(face: FT_Face, desc: *mut *mut FT_MM_Var) -> FT_Error);
ft_dyn_fn!(FT_Done_MM_Var(library: FT_Library, desc: *mut FT_MM_Var) -> FT_Error);
ft_dyn_fn!(FT_Set_Var_Design_Coordinates(face: FT_Face, num_vals: FT_UInt, vals: *mut FT_Fixed) -> FT_Error);
ft_dyn_fn!(FT_Get_Var_Design_Coordinates(face: FT_Face, num_vals: FT_UInt, vals: *mut FT_Fixed) -> FT_Error);

extern "C" {
   fn FT_GlyphSlot_Embolden(slot: FT_GlyphSlot);
}

// Custom version of FT_GlyphSlot_Embolden to be less aggressive with outline
// fonts than the default implementation in FreeType.
#[no_mangle]
pub extern "C" fn mozilla_glyphslot_embolden_less(slot: FT_GlyphSlot) {
   if slot.is_null() {
       return;
   }

   let slot_ = unsafe { &mut *slot };
   let format = slot_.format;
   if format != FT_Glyph_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(&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;
}

struct CachedFont {
   template: FontTemplate,
   face: FT_Face,
   mm_var: *mut FT_MM_Var,
   variations: Vec<FontVariation>,
}

impl Drop for CachedFont {
   fn drop(&mut self) {
       unsafe {
           if !self.mm_var.is_null() &&
               unimplemented(FT_Done_MM_Var((*(*self.face).glyph).library, self.mm_var)) {
               free(self.mm_var as _);
           }

           FT_Done_Face(self.face);
       }
   }
}

struct FontCache {
   lib: FT_Library,
   // Maps a template to a cached font that may be used across all threads.
   fonts: FastHashMap<FontTemplate, Arc<Mutex<CachedFont>>>,
   // The current LCD filter installed in the library.
   lcd_filter: FontLCDFilter,
   // The number of threads currently relying on the LCD filter state.
   lcd_filter_uses: usize,
}

// FreeType resources are safe to move between threads as long as they
// are not concurrently accessed. In our case, everything is behind a
// Mutex so it is safe to move them between threads.
unsafe impl Send for CachedFont {}
unsafe impl Send for FontCache {}

impl FontCache {
   fn new() -> Self {
       let mut lib: FT_Library = ptr::null_mut();
       let result = unsafe { FT_Init_FreeType(&mut lib) };
       if succeeded(result) {
           // Ensure the library uses the default LCD filter initially.
           unsafe { FT_Library_SetLcdFilter(lib, FT_LcdFilter::FT_LCD_FILTER_DEFAULT) };
       } else {
           panic!("Failed to initialize FreeType - {}", result)
       }

       FontCache {
           lib,
           fonts: FastHashMap::default(),
           lcd_filter: FontLCDFilter::Default,
           lcd_filter_uses: 0,
       }
   }

   fn add_font(&mut self, template: FontTemplate) -> Result<Arc<Mutex<CachedFont>>, FT_Error> {
       if let Some(cached) = self.fonts.get(&template) {
           return Ok(cached.clone());
       }
       unsafe {
           let mut face: FT_Face = ptr::null_mut();
           let result = match template {
               FontTemplate::Raw(ref bytes, index) => {
                   FT_New_Memory_Face(
                       self.lib,
                       bytes.as_ptr(),
                       bytes.len() as FT_Long,
                       index as FT_Long,
                       &mut face,
                   )
               }
               FontTemplate::Native(NativeFontHandle { ref path, index }) => {
                   let str = path.as_os_str().to_str().unwrap();
                   let cstr = CString::new(str).unwrap();
                   FT_New_Face(
                       self.lib,
                       cstr.as_ptr(),
                       index as FT_Long,
                       &mut face,
                   )
               }
           };
           if !succeeded(result) || face.is_null() {
               return Err(result);
           }
           let mut mm_var = ptr::null_mut();
           if ((*face).face_flags & (FT_FACE_FLAG_MULTIPLE_MASTERS as FT_Long)) != 0 &&
              succeeded(FT_Get_MM_Var(face, &mut mm_var)) {
               // Calling this before FT_Set_Var_Design_Coordinates avoids a bug with font variations
               // not initialized properly in the font face, even if we ignore the result.
               // See bug 1647035.
               let mut tmp = [0; 16];
               let res = FT_Get_Var_Design_Coordinates(
                   face,
                   (*mm_var).num_axis.min(16),
                   tmp.as_mut_ptr()
               );
               debug_assert!(succeeded(res));
           }
           let cached = Arc::new(Mutex::new(CachedFont {
               template: template.clone(),
               face,
               mm_var,
               variations: Vec::new(),
           }));
           self.fonts.insert(template, cached.clone());
           Ok(cached)
       }
   }

   fn delete_font(&mut self, cached: Arc<Mutex<CachedFont>>) {
       self.fonts.remove(&cached.lock().unwrap().template);
   }
}

impl Drop for FontCache {
   fn drop(&mut self) {
       self.fonts.clear();
       unsafe {
           FT_Done_FreeType(self.lib);
       }
   }
}

lazy_static! {
   static ref FONT_CACHE: Mutex<FontCache> = Mutex::new(FontCache::new());
   static ref LCD_FILTER_UNUSED: Condvar = Condvar::new();
}

pub struct FontContext {
   fonts: FastHashMap<FontKey, Arc<Mutex<CachedFont>>>,
}

fn get_skew_bounds(bottom: i32, top: i32, skew_factor: f32, _vertical: bool) -> (f32, f32) {
   let skew_min = (bottom as f32 + 0.5) * skew_factor;
   let skew_max = (top as f32 - 0.5) * skew_factor;
   // Negative skew factor may switch the sense of skew_min and skew_max.
   (skew_min.min(skew_max).floor(), skew_min.max(skew_max).ceil())
}

fn skew_bitmap(
   bitmap: &[u8],
   width: usize,
   height: usize,
   left: i32,
   top: i32,
   skew_factor: f32,
   vertical: bool, // TODO: vertical skew not yet implemented!
) -> (Vec<u8>, usize, i32) {
   let stride = width * 4;
   // Calculate the skewed horizontal offsets of the bottom and top of the glyph.
   let (skew_min, skew_max) = get_skew_bounds(top - height as i32, top, skew_factor, vertical);
   // Allocate enough extra width for the min/max skew offsets.
   let skew_width = width + (skew_max - skew_min) as usize;
   let mut skew_buffer = vec![0u8; skew_width * height * 4];
   for y in 0 .. height {
       // Calculate a skew offset at the vertical center of the current row.
       let offset = (top as f32 - y as f32 - 0.5) * skew_factor - skew_min;
       // Get a blend factor in 0..256 constant across all pixels in the row.
       let blend = (offset.fract() * 256.0) as u32;
       let src_row = y * stride;
       let dest_row = (y * skew_width + offset.floor() as usize) * 4;
       let mut prev_px = [0u32; 4];
       for (src, dest) in
           bitmap[src_row .. src_row + stride].chunks(4).zip(
               skew_buffer[dest_row .. dest_row + stride].chunks_mut(4)
           ) {
           let px = [src[0] as u32, src[1] as u32, src[2] as u32, src[3] as u32];
           // Blend current pixel with previous pixel based on blend factor.
           let next_px = [px[0] * blend, px[1] * blend, px[2] * blend, px[3] * blend];
           dest[0] = ((((px[0] << 8) - next_px[0]) + prev_px[0] + 128) >> 8) as u8;
           dest[1] = ((((px[1] << 8) - next_px[1]) + prev_px[1] + 128) >> 8) as u8;
           dest[2] = ((((px[2] << 8) - next_px[2]) + prev_px[2] + 128) >> 8) as u8;
           dest[3] = ((((px[3] << 8) - next_px[3]) + prev_px[3] + 128) >> 8) as u8;
           // Save the remainder for blending onto the next pixel.
           prev_px = next_px;
       }
       // If the skew misaligns the final pixel, write out the remainder.
       if blend > 0 {
           let dest = &mut skew_buffer[dest_row + stride .. dest_row + stride + 4];
           dest[0] = ((prev_px[0] + 128) >> 8) as u8;
           dest[1] = ((prev_px[1] + 128) >> 8) as u8;
           dest[2] = ((prev_px[2] + 128) >> 8) as u8;
           dest[3] = ((prev_px[3] + 128) >> 8) as u8;
       }
   }
   (skew_buffer, skew_width, left + skew_min as i32)
}

fn transpose_bitmap(bitmap: &[u8], width: usize, height: usize) -> Vec<u8> {
   let mut transposed = vec![0u8; width * height * 4];
   for (y, row) in bitmap.chunks(width * 4).enumerate() {
       let mut offset = y * 4;
       for src in row.chunks(4) {
           transposed[offset .. offset + 4].copy_from_slice(src);
           offset += height * 4;
       }
   }
   transposed
}

fn flip_bitmap_x(bitmap: &mut [u8], width: usize, height: usize) {
   assert!(bitmap.len() == width * height * 4);
   let pixels = unsafe { slice::from_raw_parts_mut(bitmap.as_mut_ptr() as *mut u32, width * height) };
   for row in pixels.chunks_mut(width) {
       row.reverse();
   }
}

fn flip_bitmap_y(bitmap: &mut [u8], width: usize, height: usize) {
   assert!(bitmap.len() == width * height * 4);
   let pixels = unsafe { slice::from_raw_parts_mut(bitmap.as_mut_ptr() as *mut u32, width * height) };
   for y in 0 .. height / 2 {
       let low_row = y * width;
       let high_row = (height - 1 - y) * width;
       for x in 0 .. width {
           pixels.swap(low_row + x, high_row + x);
       }
   }
}

impl FontContext {
   pub fn distribute_across_threads() -> bool {
       false
   }

   pub fn new() -> FontContext {
       FontContext {
           fonts: FastHashMap::default(),
       }
   }

   pub fn add_raw_font(&mut self, font_key: &FontKey, bytes: Arc<Vec<u8>>, index: u32) {
       if !self.fonts.contains_key(font_key) {
           let len = bytes.len();
           match FONT_CACHE.lock().unwrap().add_font(FontTemplate::Raw(bytes, index)) {
               Ok(font) => self.fonts.insert(*font_key, font),
               Err(result) => panic!("adding raw font failed: {} bytes, err={:?}", len, result),
           };
       }
   }

   pub fn add_native_font(&mut self, font_key: &FontKey, native_font_handle: NativeFontHandle) {
       if !self.fonts.contains_key(font_key) {
           let path = native_font_handle.path.to_string_lossy().into_owned();
           match FONT_CACHE.lock().unwrap().add_font(FontTemplate::Native(native_font_handle)) {
               Ok(font) => self.fonts.insert(*font_key, font),
               Err(result) => panic!("adding native font failed: file={} err={:?}", path, result),
           };
       }
   }

   pub fn delete_font(&mut self, font_key: &FontKey) {
       if let Some(cached) = self.fonts.remove(font_key) {
           // If the only references to this font are the FontCache and this FontContext,
           // then delete the font as there are no other existing users.
           if Arc::strong_count(&cached) <= 2 {
               FONT_CACHE.lock().unwrap().delete_font(cached);
           }
       }
   }

   pub fn delete_font_instance(&mut self, _instance: &FontInstance) {
   }

   fn load_glyph(&mut self, font: &FontInstance, glyph: &GlyphKey)
       -> Option<(MutexGuard<CachedFont>, FT_GlyphSlot, f32)> {
       let mut cached = self.fonts.get(&font.font_key)?.lock().ok()?;
       let face = cached.face;

       let mm_var = cached.mm_var;
       if !mm_var.is_null() && font.variations != cached.variations {
           cached.variations.clear();
           cached.variations.extend_from_slice(&font.variations);

           unsafe {
               let num_axis = (*mm_var).num_axis;
               let mut coords: Vec<FT_Fixed> = Vec::with_capacity(num_axis as usize);
               for i in 0 .. num_axis {
                   let axis = (*mm_var).axis.offset(i as isize);
                   let mut value = (*axis).def;
                   for var in &font.variations {
                       if var.tag as FT_ULong == (*axis).tag {
                           value = (var.value * 65536.0 + 0.5) as FT_Fixed;
                           value = cmp::min(value, (*axis).maximum);
                           value = cmp::max(value, (*axis).minimum);
                           break;
                       }
                   }
                   coords.push(value);
               }
               let res = FT_Set_Var_Design_Coordinates(face, num_axis, coords.as_mut_ptr());
               debug_assert!(succeeded(res));
           }
       }

       let mut load_flags = FT_LOAD_DEFAULT;
       let FontInstancePlatformOptions { mut hinting, .. } = font.platform_options.unwrap_or_default();
       // Disable hinting if there is a non-axis-aligned transform.
       if font.synthetic_italics.is_enabled() ||
          ((font.transform.scale_x != 0.0 || font.transform.scale_y != 0.0) &&
           (font.transform.skew_x != 0.0 || font.transform.skew_y != 0.0)) {
           hinting = FontHinting::None;
       }
       match (hinting, font.render_mode) {
           (FontHinting::None, _) => load_flags |= FT_LOAD_NO_HINTING,
           (FontHinting::Mono, _) => load_flags = FT_LOAD_TARGET_MONO,
           (FontHinting::Light, _) => load_flags = FT_LOAD_TARGET_LIGHT,
           (FontHinting::LCD, FontRenderMode::Subpixel) => {
               load_flags = if font.flags.contains(FontInstanceFlags::LCD_VERTICAL) {
                   FT_LOAD_TARGET_LCD_V
               } else {
                   FT_LOAD_TARGET_LCD
               };
               if font.flags.contains(FontInstanceFlags::FORCE_AUTOHINT) {
                   load_flags |= FT_LOAD_FORCE_AUTOHINT;
               }
           }
           _ => {
               if font.flags.contains(FontInstanceFlags::FORCE_AUTOHINT) {
                   load_flags |= FT_LOAD_FORCE_AUTOHINT;
               }
           }
       }

       if font.flags.contains(FontInstanceFlags::NO_AUTOHINT) {
           load_flags |= FT_LOAD_NO_AUTOHINT;
       }
       if !font.flags.contains(FontInstanceFlags::EMBEDDED_BITMAPS) {
           load_flags |= FT_LOAD_NO_BITMAP;
       }

       let face_flags = unsafe { (*face).face_flags };
       if (face_flags & (FT_FACE_FLAG_FIXED_SIZES as FT_Long)) != 0 {
         // We only set FT_LOAD_COLOR if there are bitmap strikes;
         // COLR (color-layer) fonts are handled internally by Gecko, and
         // WebRender is just asked to paint individual layers.
         load_flags |= FT_LOAD_COLOR;
       }

       load_flags |= FT_LOAD_IGNORE_GLOBAL_ADVANCE_WIDTH;

       let (x_scale, y_scale) = font.transform.compute_scale().unwrap_or((1.0, 1.0));
       let req_size = font.size.to_f64_px();

       let mut result = if (face_flags & (FT_FACE_FLAG_FIXED_SIZES as FT_Long)) != 0 &&
                           (face_flags & (FT_FACE_FLAG_SCALABLE as FT_Long)) == 0 &&
                           (load_flags & FT_LOAD_NO_BITMAP) == 0 {
           unsafe { FT_Set_Transform(face, ptr::null_mut(), ptr::null_mut()) };
           self.choose_bitmap_size(face, req_size * y_scale)
       } else {
           let mut shape = font.transform.invert_scale(x_scale, y_scale);
           if font.flags.contains(FontInstanceFlags::FLIP_X) {
               shape = shape.flip_x();
           }
           if font.flags.contains(FontInstanceFlags::FLIP_Y) {
               shape = shape.flip_y();
           }
           if font.flags.contains(FontInstanceFlags::TRANSPOSE) {
               shape = shape.swap_xy();
           }
           let (mut tx, mut ty) = (0.0, 0.0);
           if font.synthetic_italics.is_enabled() {
               let (shape_, (tx_, ty_)) = font.synthesize_italics(shape, y_scale * req_size);
               shape = shape_;
               tx = tx_;
               ty = ty_;
           };
           let mut ft_shape = FT_Matrix {
               xx: (shape.scale_x * 65536.0) as FT_Fixed,
               xy: (shape.skew_x * -65536.0) as FT_Fixed,
               yx: (shape.skew_y * -65536.0) as FT_Fixed,
               yy: (shape.scale_y * 65536.0) as FT_Fixed,
           };
           // The delta vector for FT_Set_Transform is in units of 1/64 pixel.
           let mut ft_delta = FT_Vector {
               x: (tx * 64.0) as FT_F26Dot6,
               y: (ty * -64.0) as FT_F26Dot6,
           };
           unsafe {
               FT_Set_Transform(face, &mut ft_shape, &mut ft_delta);
               FT_Set_Char_Size(
                   face,
                   (req_size * x_scale * 64.0 + 0.5) as FT_F26Dot6,
                   (req_size * y_scale * 64.0 + 0.5) as FT_F26Dot6,
                   0,
                   0,
               )
           }
       };

       if !succeeded(result) {
           error!("Unable to set glyph size and transform: {}", result);
           //let raw_error = unsafe { FT_Error_String(result) };
           //if !raw_error.is_ptr() {
           //    error!("\tcode {:?}", CStr::from_ptr(raw_error));
           //}
           debug!(
               "\t[{}] for size {:?} and scale {:?} from font {:?}",
               glyph.index(),
               req_size,
               (x_scale, y_scale),
               font.font_key,
           );
           return None;
       }

       result = unsafe { FT_Load_Glyph(face, glyph.index() as FT_UInt, load_flags as FT_Int32) };
       if !succeeded(result) {
           error!("Unable to load glyph: {}", result);
           //let raw_error = unsafe { FT_Error_String(result) };
           //if !raw_error.is_ptr() {
           //    error!("\tcode {:?}", CStr::from_ptr(raw_error));
           //}
           debug!(
               "\t[{}] with flags {:?} from font {:?}",
               glyph.index(),
               load_flags,
               font.font_key,
           );
           return None;
       }

       let slot = unsafe { (*face).glyph };
       assert!(slot != ptr::null_mut());

       if font.flags.contains(FontInstanceFlags::SYNTHETIC_BOLD) {
           mozilla_glyphslot_embolden_less(slot);
       }

       let format = unsafe { (*slot).format };
       match format {
           FT_Glyph_Format::FT_GLYPH_FORMAT_BITMAP => {
               let bitmap_size = unsafe { (*(*(*slot).face).size).metrics.y_ppem };
               Some((cached, slot, req_size as f32 / bitmap_size as f32))
           }
           FT_Glyph_Format::FT_GLYPH_FORMAT_OUTLINE => Some((cached, slot, 1.0)),
           _ => {
               error!("Unsupported format");
               debug!("format={:?}", format);
               None
           }
       }
   }

   fn pad_bounding_box(font: &FontInstance, cbox: &mut FT_BBox) {
       // Apply extra pixel of padding for subpixel AA, due to the filter.
       if font.render_mode == FontRenderMode::Subpixel {
           // Using an LCD filter may add one full pixel to each side if support is built in.
           // As of FreeType 2.8.1, an LCD filter is always used regardless of settings
           // if support for the patent-encumbered LCD filter algorithms is not built in.
           // Thus, the only reasonable way to guess padding is to unconditonally add it if
           // subpixel AA is used.
           let lcd_extra_pixels = 1;
           let padding = (lcd_extra_pixels * 64) as FT_Pos;
           if font.flags.contains(FontInstanceFlags::LCD_VERTICAL) {
               cbox.yMin -= padding;
               cbox.yMax += padding;
           } else {
               cbox.xMin -= padding;
               cbox.xMax += padding;
           }
       }
   }

   // Get the bounding box for a glyph, accounting for sub-pixel positioning.
   fn get_bounding_box(
       slot: FT_GlyphSlot,
       font: &FontInstance,
       glyph: &GlyphKey,
       scale: f32,
   ) -> FT_BBox {
       // Get the estimated bounding box from FT (control points).
       let mut cbox = FT_BBox { xMin: 0, yMin: 0, xMax: 0, yMax: 0 };

       unsafe {
           FT_Outline_Get_CBox(&(*slot).outline, &mut cbox);
       }

       // For spaces and other non-printable characters, early out.
       if unsafe { (*slot).outline.n_contours } == 0 {
           return cbox;
       }

       Self::pad_bounding_box(font, &mut cbox);

       // Offset the bounding box by subpixel positioning.
       // Convert to 26.6 fixed point format for FT.
       let (dx, dy) = font.get_subpx_offset(glyph);
       let (dx, dy) = (
           (dx / scale as f64 * 64.0 + 0.5) as FT_Pos,
           -(dy / scale as f64 * 64.0 + 0.5) as FT_Pos,
       );
       cbox.xMin += dx;
       cbox.xMax += dx;
       cbox.yMin += dy;
       cbox.yMax += dy;

       // Outset the box to device pixel boundaries
       cbox.xMin &= !63;
       cbox.yMin &= !63;
       cbox.xMax = (cbox.xMax + 63) & !63;
       cbox.yMax = (cbox.yMax + 63) & !63;

       cbox
   }

   fn get_glyph_dimensions_impl(
       slot: FT_GlyphSlot,
       font: &FontInstance,
       glyph: &GlyphKey,
       scale: f32,
       use_transform: bool,
   ) -> Option<GlyphDimensions> {
       let format = unsafe { (*slot).format };
       let (mut left, mut top, mut width, mut height) = match format {
           FT_Glyph_Format::FT_GLYPH_FORMAT_BITMAP => {
               unsafe { (
                   (*slot).bitmap_left as i32,
                   (*slot).bitmap_top as i32,
                   (*slot).bitmap.width as i32,
                   (*slot).bitmap.rows as i32,
               ) }
           }
           FT_Glyph_Format::FT_GLYPH_FORMAT_OUTLINE => {
               let cbox = Self::get_bounding_box(slot, font, glyph, scale);
               (
                   (cbox.xMin >> 6) as i32,
                   (cbox.yMax >> 6) as i32,
                   ((cbox.xMax - cbox.xMin) >> 6) as i32,
                   ((cbox.yMax - cbox.yMin) >> 6) as i32,
               )
           }
           _ => return None,
       };
       let mut advance = unsafe { (*slot).metrics.horiAdvance as f32 / 64.0 };
       if use_transform {
           if scale != 1.0 {
               let x0 = left as f32 * scale;
               let x1 = width as f32 * scale + x0;
               let y1 = top as f32 * scale;
               let y0 = y1 - height as f32 * scale;
               left = x0.round() as i32;
               top = y1.round() as i32;
               width = (x1.ceil() - x0.floor()) as i32;
               height = (y1.ceil() - y0.floor()) as i32;
               advance *= scale;
           }
           // An outline glyph's cbox would have already been transformed inside FT_Load_Glyph,
           // so only handle bitmap glyphs which are not handled by FT_Load_Glyph.
           if format == FT_Glyph_Format::FT_GLYPH_FORMAT_BITMAP {
               if font.synthetic_italics.is_enabled() {
                   let (skew_min, skew_max) = get_skew_bounds(
                       top - height as i32,
                       top,
                       font.synthetic_italics.to_skew(),
                       font.flags.contains(FontInstanceFlags::VERTICAL),
                   );
                   left += skew_min as i32;
                   width += (skew_max - skew_min) as i32;
               }
               if font.flags.contains(FontInstanceFlags::TRANSPOSE) {
                   mem::swap(&mut width, &mut height);
                   mem::swap(&mut left, &mut top);
                   left -= width as i32;
                   top += height as i32;
               }
               if font.flags.contains(FontInstanceFlags::FLIP_X) {
                   left = -(left + width as i32);
               }
               if font.flags.contains(FontInstanceFlags::FLIP_Y) {
                   top = -(top - height as i32);
               }
           }
       }
       Some(GlyphDimensions {
           left,
           top,
           width,
           height,
           advance,
       })
   }

   pub fn get_glyph_index(&mut self, font_key: FontKey, ch: char) -> Option<u32> {
       let cached = self.fonts.get(&font_key)?.lock().ok()?;
       let face = cached.face;
       unsafe {
           let idx = FT_Get_Char_Index(face, ch as _);
           if idx != 0 {
               Some(idx)
           } else {
               None
           }
       }
   }

   pub fn get_glyph_dimensions(
       &mut self,
       font: &FontInstance,
       key: &GlyphKey,
   ) -> Option<GlyphDimensions> {
       let (_cached, slot, scale) = self.load_glyph(font, key)?;
       Self::get_glyph_dimensions_impl(slot, &font, key, scale, true)
   }

   fn choose_bitmap_size(&self, face: FT_Face, requested_size: f64) -> FT_Error {
       let mut best_dist = unsafe { *(*face).available_sizes.offset(0) }.y_ppem as f64 / 64.0 - requested_size;
       let mut best_size = 0;
       let num_fixed_sizes = unsafe { (*face).num_fixed_sizes };
       for i in 1 .. num_fixed_sizes {
           // Distance is positive if strike is larger than desired size,
           // or negative if smaller. If previously a found smaller strike,
           // then prefer a larger strike. Otherwise, minimize distance.
           let dist = unsafe { *(*face).available_sizes.offset(i as isize) }.y_ppem as f64 / 64.0 - requested_size;
           if (best_dist < 0.0 && dist >= best_dist) || dist.abs() <= best_dist {
               best_dist = dist;
               best_size = i;
           }
       }
       unsafe { FT_Select_Size(face, best_size) }
   }

   pub fn prepare_font(font: &mut FontInstance) {
       match font.render_mode {
           FontRenderMode::Mono => {
               // In mono mode the color of the font is irrelevant.
               font.color = ColorU::new(0xFF, 0xFF, 0xFF, 0xFF);
               // Subpixel positioning is disabled in mono mode.
               font.disable_subpixel_position();
           }
           FontRenderMode::Alpha => {
               if FONT_GAMMA > 0.0 {
                   font.color = font.color.luminance_color().quantize();
               } else {
                   // Color is unused if there is no preblend.
                   font.color = ColorU::new(0xFF, 0xFF, 0xFF, 0xFF);
               }
           }
           FontRenderMode::Subpixel => {
               if FONT_GAMMA > 0.0 {
                   font.color = font.color.quantize();
               } else {
                   // Color is unused if there is no preblend.
                   font.color = ColorU::new(0xFF, 0xFF, 0xFF, 0xFF);
               }
           }
       }
   }

   fn rasterize_glyph_outline(
       slot: FT_GlyphSlot,
       font: &FontInstance,
       key: &GlyphKey,
       scale: f32,
   ) -> bool {
       // Get the subpixel offsets in FT 26.6 format.
       let (dx, dy) = font.get_subpx_offset(key);
       let (dx, dy) = (
           (dx / scale as f64 * 64.0 + 0.5) as FT_Pos,
           -(dy / scale as f64 * 64.0 + 0.5) as FT_Pos,
       );

       // Move the outline curves to be at the origin, taking
       // into account the subpixel positioning.
       unsafe {
           let outline = &(*slot).outline;
           let mut cbox = FT_BBox { xMin: 0, yMin: 0, xMax: 0, yMax: 0 };
           FT_Outline_Get_CBox(outline, &mut cbox);
           Self::pad_bounding_box(font, &mut cbox);
           FT_Outline_Translate(
               outline,
               dx - ((cbox.xMin + dx) & !63),
               dy - ((cbox.yMin + dy) & !63),
           );
       }

       let render_mode = match font.render_mode {
           FontRenderMode::Mono => FT_Render_Mode::FT_RENDER_MODE_MONO,
           FontRenderMode::Alpha => FT_Render_Mode::FT_RENDER_MODE_NORMAL,
           FontRenderMode::Subpixel => if font.flags.contains(FontInstanceFlags::LCD_VERTICAL) {
               FT_Render_Mode::FT_RENDER_MODE_LCD_V
           } else {
               FT_Render_Mode::FT_RENDER_MODE_LCD
           },
       };
       let result = unsafe { FT_Render_Glyph(slot, render_mode) };
       if !succeeded(result) {
           error!("Unable to rasterize");
           debug!(
               "{:?} with {:?}, {:?}",
               key,
               render_mode,
               result
           );
           false
       } else {
           true
       }
   }

   pub fn begin_rasterize(font: &FontInstance) {
       // The global LCD filter state is only used in subpixel rendering modes.
       if font.render_mode == FontRenderMode::Subpixel {
           let mut cache = FONT_CACHE.lock().unwrap();
           let FontInstancePlatformOptions { lcd_filter, .. } = font.platform_options.unwrap_or_default();
           // Check if the current LCD filter matches the requested one.
           if cache.lcd_filter != lcd_filter {
               // If the filter doesn't match, we have to wait for all other currently rasterizing threads
               // that may use the LCD filter state to finish before we can override it.
               while cache.lcd_filter_uses != 0 {
                   cache = LCD_FILTER_UNUSED.wait(cache).unwrap();
               }
               // Finally set the LCD filter to the requested one now that the library is unused.
               cache.lcd_filter = lcd_filter;
               let filter = match lcd_filter {
                   FontLCDFilter::None => FT_LcdFilter::FT_LCD_FILTER_NONE,
                   FontLCDFilter::Default => FT_LcdFilter::FT_LCD_FILTER_DEFAULT,
                   FontLCDFilter::Light => FT_LcdFilter::FT_LCD_FILTER_LIGHT,
                   FontLCDFilter::Legacy => FT_LcdFilter::FT_LCD_FILTER_LEGACY,
               };
               unsafe {
                   let result = FT_Library_SetLcdFilter(cache.lib, filter);
                   // Setting the legacy filter may fail, so just use the default filter instead.
                   if !succeeded(result) {
                       FT_Library_SetLcdFilter(cache.lib, FT_LcdFilter::FT_LCD_FILTER_DEFAULT);
                   }
               }
           }
           cache.lcd_filter_uses += 1;
       }
   }

   pub fn end_rasterize(font: &FontInstance) {
       if font.render_mode == FontRenderMode::Subpixel {
           let mut cache = FONT_CACHE.lock().unwrap();
           // If this is the last use of the LCD filter, then signal that the LCD filter isn't used.
           cache.lcd_filter_uses -= 1;
           if cache.lcd_filter_uses == 0 {
               LCD_FILTER_UNUSED.notify_all();
           }
       }
   }

   pub fn rasterize_glyph(&mut self, font: &FontInstance, key: &GlyphKey) -> GlyphRasterResult {
       let (_cached, slot, scale) = self.load_glyph(font, key)
                                        .ok_or(GlyphRasterError::LoadFailed)?;

       // Get dimensions of the glyph, to see if we need to rasterize it.
       // Don't apply scaling to the dimensions, as the glyph cache needs to know the actual
       // footprint of the glyph.
       let dimensions = Self::get_glyph_dimensions_impl(slot, font, key, scale, false)
                            .ok_or(GlyphRasterError::LoadFailed)?;
       let GlyphDimensions { mut left, mut top, width, height, .. } = dimensions;

       // For spaces and other non-printable characters, early out.
       if width == 0 || height == 0 {
           return Err(GlyphRasterError::LoadFailed);
       }

       let format = unsafe { (*slot).format };
       match format {
           FT_Glyph_Format::FT_GLYPH_FORMAT_BITMAP => {}
           FT_Glyph_Format::FT_GLYPH_FORMAT_OUTLINE => {
               if !Self::rasterize_glyph_outline(slot, font, key, scale) {
                   return Err(GlyphRasterError::LoadFailed);
               }
           }
           _ => {
               error!("Unsupported format");
               debug!("format={:?}", format);
               return Err(GlyphRasterError::LoadFailed);
           }
       };

       debug!(
           "Rasterizing {:?} as {:?} with dimensions {:?}",
           key,
           font.render_mode,
           dimensions
       );

       let bitmap = unsafe { &(*slot).bitmap };
       let pixel_mode = unsafe { mem::transmute(bitmap.pixel_mode as u32) };
       let (mut actual_width, mut actual_height) = match pixel_mode {
           FT_Pixel_Mode::FT_PIXEL_MODE_LCD => {
               assert!(bitmap.width % 3 == 0);
               ((bitmap.width / 3) as usize, bitmap.rows as usize)
           }
           FT_Pixel_Mode::FT_PIXEL_MODE_LCD_V => {
               assert!(bitmap.rows % 3 == 0);
               (bitmap.width as usize, (bitmap.rows / 3) as usize)
           }
           FT_Pixel_Mode::FT_PIXEL_MODE_MONO |
           FT_Pixel_Mode::FT_PIXEL_MODE_GRAY |
           FT_Pixel_Mode::FT_PIXEL_MODE_BGRA => {
               (bitmap.width as usize, bitmap.rows as usize)
           }
           _ => panic!("Unsupported mode"),
       };

       // If we need padding, we will need to expand the buffer size.
       let (buffer_width, buffer_height, padding) = if font.use_texture_padding() {
           (actual_width + 2, actual_height + 2, 1)
       } else {
           (actual_width, actual_height, 0)
       };

       let mut final_buffer = vec![0u8; buffer_width * buffer_height * 4];

       // Extract the final glyph from FT format into BGRA8 format, which is
       // what WR expects.
       let subpixel_bgr = font.flags.contains(FontInstanceFlags::SUBPIXEL_BGR);
       let mut src_row = bitmap.buffer;
       let mut dest = 4 * padding * (padding + buffer_width);
       let actual_end = final_buffer.len() - 4 * padding * (buffer_width + 1);
       while dest < actual_end {
           let mut src = src_row;
           let row_end = dest + actual_width * 4;
           match pixel_mode {
               FT_Pixel_Mode::FT_PIXEL_MODE_MONO => {
                   while dest < row_end {
                       // Cast the byte to signed so that we can left shift each bit into
                       // the top bit, then right shift to fill out the bits with 0s or 1s.
                       let mut byte: i8 = unsafe { *src as i8 };
                       src = unsafe { src.offset(1) };
                       let byte_end = cmp::min(row_end, dest + 8 * 4);
                       while dest < byte_end {
                           let alpha = (byte >> 7) as u8;
                           final_buffer[dest + 0] = alpha;
                           final_buffer[dest + 1] = alpha;
                           final_buffer[dest + 2] = alpha;
                           final_buffer[dest + 3] = alpha;
                           dest += 4;
                           byte <<= 1;
                       }
                   }
               }
               FT_Pixel_Mode::FT_PIXEL_MODE_GRAY => {
                   while dest < row_end {
                       let alpha = unsafe { *src };
                       final_buffer[dest + 0] = alpha;
                       final_buffer[dest + 1] = alpha;
                       final_buffer[dest + 2] = alpha;
                       final_buffer[dest + 3] = alpha;
                       src = unsafe { src.offset(1) };
                       dest += 4;
                   }
               }
               FT_Pixel_Mode::FT_PIXEL_MODE_LCD => {
                   while dest < row_end {
                       let (mut r, g, mut b) = unsafe { (*src, *src.offset(1), *src.offset(2)) };
                       if subpixel_bgr {
                           mem::swap(&mut r, &mut b);
                       }
                       final_buffer[dest + 0] = b;
                       final_buffer[dest + 1] = g;
                       final_buffer[dest + 2] = r;
                       final_buffer[dest + 3] = max(max(b, g), r);
                       src = unsafe { src.offset(3) };
                       dest += 4;
                   }
               }
               FT_Pixel_Mode::FT_PIXEL_MODE_LCD_V => {
                   while dest < row_end {
                       let (mut r, g, mut b) =
                           unsafe { (*src, *src.offset(bitmap.pitch as isize),
                                     *src.offset((2 * bitmap.pitch) as isize)) };
                       if subpixel_bgr {
                           mem::swap(&mut r, &mut b);
                       }
                       final_buffer[dest + 0] = b;
                       final_buffer[dest + 1] = g;
                       final_buffer[dest + 2] = r;
                       final_buffer[dest + 3] = max(max(b, g), r);
                       src = unsafe { src.offset(1) };
                       dest += 4;
                   }
                   src_row = unsafe { src_row.offset((2 * bitmap.pitch) as isize) };
               }
               FT_Pixel_Mode::FT_PIXEL_MODE_BGRA => {
                   // The source is premultiplied BGRA data.
                   let dest_slice = &mut final_buffer[dest .. row_end];
                   let src_slice = unsafe { slice::from_raw_parts(src, dest_slice.len()) };
                   dest_slice.copy_from_slice(src_slice);
               }
               _ => panic!("Unsupported mode"),
           }
           src_row = unsafe { src_row.offset(bitmap.pitch as isize) };
           dest = row_end + 8 * padding;
       }

       if FONT_GAMMA > 0.0 &&
          pixel_mode != FT_Pixel_Mode::FT_PIXEL_MODE_MONO &&
          pixel_mode != FT_Pixel_Mode::FT_PIXEL_MODE_BGRA {
         GAMMA_LUT.preblend(&mut final_buffer, font.color);
       }

       if font.use_texture_padding() {
           left -= padding as i32;
           top += padding as i32;
           actual_width = buffer_width;
           actual_height = buffer_height;
       }

       match format {
           FT_Glyph_Format::FT_GLYPH_FORMAT_BITMAP => {
               if font.synthetic_italics.is_enabled() {
                   let (skew_buffer, skew_width, skew_left) = skew_bitmap(
                       &final_buffer,
                       actual_width,
                       actual_height,
                       left,
                       top,
                       font.synthetic_italics.to_skew(),
                       font.flags.contains(FontInstanceFlags::VERTICAL),
                   );
                   final_buffer = skew_buffer;
                   actual_width = skew_width;
                   left = skew_left;
               }
               if font.flags.contains(FontInstanceFlags::TRANSPOSE) {
                   final_buffer = transpose_bitmap(&final_buffer, actual_width, actual_height);
                   mem::swap(&mut actual_width, &mut actual_height);
                   mem::swap(&mut left, &mut top);
                   left -= actual_width as i32;
                   top += actual_height as i32;
               }
               if font.flags.contains(FontInstanceFlags::FLIP_X) {
                   flip_bitmap_x(&mut final_buffer, actual_width, actual_height);
                   left = -(left + actual_width as i32);
               }
               if font.flags.contains(FontInstanceFlags::FLIP_Y) {
                   flip_bitmap_y(&mut final_buffer, actual_width, actual_height);
                   top = -(top - actual_height as i32);
               }
           }
           FT_Glyph_Format::FT_GLYPH_FORMAT_OUTLINE => {
               unsafe {
                   left += (*slot).bitmap_left;
                   top += (*slot).bitmap_top - height as i32;
               }
           }
           _ => {}
       }

       let glyph_format = match (pixel_mode, format) {
           (FT_Pixel_Mode::FT_PIXEL_MODE_LCD, _) |
           (FT_Pixel_Mode::FT_PIXEL_MODE_LCD_V, _) => font.get_subpixel_glyph_format(),
           (FT_Pixel_Mode::FT_PIXEL_MODE_BGRA, _) => GlyphFormat::ColorBitmap,
           (_, FT_Glyph_Format::FT_GLYPH_FORMAT_BITMAP) => GlyphFormat::Bitmap,
           _ => font.get_alpha_glyph_format(),
       };

       Ok(RasterizedGlyph {
           left: left as f32,
           top: top as f32,
           width: actual_width as i32,
           height: actual_height as i32,
           scale,
           format: glyph_format,
           bytes: final_buffer,
           is_packed_glyph: false,
       })
   }
}