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Take on smallvec in read-fonts and skrifa #2081

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9 changes: 9 additions & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,15 @@ rust-version = "1.85"
# Chrome: https://chromium.googlesource.com/chromium/src/third_party/rust/+/refs/heads/main/bytemuck/v1/BUILD.gn
# Android: https://android.googlesource.com/platform/external/rust/crates/bytemuck/+/refs/heads/main/Cargo.toml
bytemuck = "1.14.0"
# note: as with bytemuck, the smallvec version must be available in all
# deployment environments, specifically the floor of the versions supported by
# google3, Chrome and Android.
# Chrome: https://chromium.googlesource.com/chromium/src/third_party/rust/+/refs/heads/main/smallvec/v1/BUILD.gn
# Android: https://android.googlesource.com/platform/external/rust/crates/smallvec/+/refs/heads/main/Cargo.toml
smallvec = { version = "1.13.1", default-features = false, features = [
"const_generics",
"union",
] }
# dev dependencies
env_logger = "0.11"
pretty_assertions = "1.3.0"
Expand Down
1 change: 1 addition & 0 deletions read-fonts/Cargo.toml
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Expand Up @@ -38,6 +38,7 @@ libm = ["dep:core_maths"]
agl = []

[dependencies]
smallvec = { workspace = true }
font-types = { workspace = true, features = ["bytemuck"] }
serde = { version = "1.0", features = ["derive"], optional = true }
core_maths = { workspace = true, optional = true }
Expand Down
109 changes: 22 additions & 87 deletions read-fonts/src/model/font/instance.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,11 +9,11 @@ use crate::{
},
TableProvider,
};
use alloc::vec::Vec;
use core::{
str::FromStr,
sync::atomic::{self, AtomicU32},
};
use smallvec::SmallVec;
use types::{Fixed, Tag};

/// A specific instance of a font, with a size and variation settings.
Expand All @@ -31,7 +31,7 @@ impl FontInstance {
instance: Self {
font: font.clone(),
size: None,
coords: CoordStorage::default(),
coords: CoordStorage::new(),
feature_vars: FeatureVarsStorage::new(),
},
}
Expand Down Expand Up @@ -157,24 +157,24 @@ impl FontInstanceBuilder {
variations,
);
} else {
self.instance.coords.resize(0);
self.instance.coords.clear();
}
}

fn set_coords(&mut self, coords: impl IntoIterator<Item = NormalizedCoord>) {
if let Ok(fvar) = self.instance.font.tables().fvar() {
let count = fvar.axis_count() as usize;
self.instance.coords.resize(count);
self.instance.coords.resize(count, NormalizedCoord::ZERO);
for (dst, src) in self.instance.coords.as_mut_slice().iter_mut().zip(
coords
.into_iter()
.chain(core::iter::repeat(NormalizedCoord::ZERO)),
) {
*dst = src;
}
self.instance.coords.clear_if_all_zeroes();
clear_if_all_zeroes(&mut self.instance.coords);
} else {
self.instance.coords.resize(0);
self.instance.coords.clear();
}
}

Expand All @@ -188,7 +188,7 @@ impl FontInstanceBuilder {
named_instance_variations(&fvar, index),
);
} else {
self.instance.coords.resize(0);
self.instance.coords.clear();
}
}

Expand All @@ -207,7 +207,7 @@ impl FontInstanceBuilder {
.chain(overrides.into_iter().map(Into::into)),
);
} else {
self.instance.coords.resize(0);
self.instance.coords.clear();
}
}
}
Expand Down Expand Up @@ -239,7 +239,7 @@ where
V: IntoIterator,
V::Item: Into<FontVariation>,
{
coords.resize(fvar.axis_count() as usize);
coords.resize(fvar.axis_count() as usize, NormalizedCoord::ZERO);
fvar.user_to_normalized(
avar.as_ref(),
variations
Expand All @@ -248,7 +248,7 @@ where
.map(|var| (var.tag, Fixed::from_f64(var.value as _))),
coords.as_mut_slice(),
);
coords.clear_if_all_zeroes();
clear_if_all_zeroes(coords);
}

/// A normalized variation coordinate in 2.14 fixed point in the range
Expand Down Expand Up @@ -309,85 +309,20 @@ impl From<&(&str, f32)> for FontVariation {
}
}

/// Maximum number of coordinates we store inline. Chosen to maximize
/// number of coords while minimizing space overhead.
const MAX_INLINE_COORDS: usize = 15;
/// Maximum number of coordinates we store inline. Chosen to maximize the
/// number of coords without growing the storage: a `SmallVec` is a capacity
/// alongside a union of the inline array and the heap pointer, so twelve
/// two byte coords are the most that fit in the same 32 bytes the previous
/// hand rolled storage took.
const MAX_INLINE_COORDS: usize = 12;

enum CoordStorage {
None,
Inline([NormalizedCoord; MAX_INLINE_COORDS], u8),
Heap(Vec<NormalizedCoord>),
}

impl Default for CoordStorage {
fn default() -> Self {
Self::None
}
}

impl CoordStorage {
/// Empty storage if all the coordinates are zeros. This allows us to
/// bypass variation processing for the default instance with a simple
/// is_empty() check.
fn clear_if_all_zeroes(&mut self) {
match self {
Self::None => {}
Self::Inline(coords, len) => {
if coords[..*len as usize]
.iter()
.all(|&c| c == NormalizedCoord::ZERO)
{
*len = 0;
}
}
Self::Heap(heap) => {
if heap.iter().all(|&c| c == NormalizedCoord::ZERO) {
heap.clear();
}
}
}
}
type CoordStorage = SmallVec<[NormalizedCoord; MAX_INLINE_COORDS]>;

fn resize(&mut self, new_len: usize) {
match self {
Self::None => {
if new_len > MAX_INLINE_COORDS {
let mut heap = Vec::with_capacity(new_len);
heap.resize(new_len, NormalizedCoord::ZERO);
*self = Self::Heap(heap);
} else {
*self = Self::Inline([NormalizedCoord::ZERO; MAX_INLINE_COORDS], new_len as u8);
}
}
Self::Inline(_, len) => {
if new_len > MAX_INLINE_COORDS {
let mut heap = Vec::with_capacity(new_len);
heap.resize(new_len, NormalizedCoord::ZERO);
*self = Self::Heap(heap);
} else {
*len = new_len as u8;
}
}
Self::Heap(heap) => {
heap.resize(new_len, NormalizedCoord::ZERO);
}
}
}

fn as_slice(&self) -> &[NormalizedCoord] {
match self {
Self::None => &[],
Self::Inline(coords, len) => &coords[..*len as usize],
Self::Heap(heap) => heap.as_slice(),
}
}

fn as_mut_slice(&mut self) -> &mut [NormalizedCoord] {
match self {
Self::None => &mut [],
Self::Inline(coords, len) => &mut coords[..*len as usize],
Self::Heap(heap) => heap.as_mut_slice(),
}
/// Empties `coords` if every coordinate is zero. This lets the default
/// instance skip variation processing behind a plain `is_empty` check.
fn clear_if_all_zeroes(coords: &mut CoordStorage) {
if coords.iter().all(|&c| c == NormalizedCoord::ZERO) {
coords.clear();
}
}

Expand Down
34 changes: 9 additions & 25 deletions read-fonts/src/tables/fvar.rs
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Expand Up @@ -6,7 +6,7 @@ include!("../../generated/generated_fvar.rs");
mod instance_record;

use super::{avar::Avar, variations::DeltaSetIndex};
use alloc::vec::Vec;
use smallvec::SmallVec;

pub use instance_record::InstanceRecord;

Expand Down Expand Up @@ -60,14 +60,8 @@ fn normalize_user_coords<T>(
return;
}
// Above MAX_NORMALIZE_QUADRATIC_AXES, use an indexed path to avoid O(n^2) behavior
let mut stack_axis_order = [0u16; MAX_INLINE_NORMALIZE_AXES];
let mut heap_axis_order = Vec::new();
let axis_order = if axis_count > MAX_INLINE_NORMALIZE_AXES {
heap_axis_order.resize(axis_count, 0);
heap_axis_order.as_mut_slice()
} else {
&mut stack_axis_order[..axis_count]
};
let mut axis_order = SmallVec::<[u16; MAX_INLINE_NORMALIZE_AXES]>::from_elem(0, axis_count);
let axis_order = axis_order.as_mut_slice();
// Initialize axis_order with the identity mapping
for (i, axis_index) in axis_order.iter_mut().enumerate() {
*axis_index = i as u16;
Expand Down Expand Up @@ -147,14 +141,9 @@ impl<'a> Fvar<'a> {
let actual_len = axes.len().min(normalized_coords.len());
let normalized_coords = &mut normalized_coords[..actual_len];

let mut stack_fixed_coords = [Fixed::ZERO; MAX_INLINE_AVAR2_AXES];
let mut heap_fixed_coords = Vec::new();
let fixed_coords = if actual_len > MAX_INLINE_AVAR2_AXES {
heap_fixed_coords.resize(actual_len, Fixed::ZERO);
heap_fixed_coords.as_mut_slice()
} else {
&mut stack_fixed_coords[..actual_len]
};
let mut fixed_coords =
SmallVec::<[Fixed; MAX_INLINE_AVAR2_AXES]>::from_elem(Fixed::ZERO, actual_len);
let fixed_coords = fixed_coords.as_mut_slice();
normalize_user_coords(axes, user_coords, fixed_coords, core::convert::identity);
apply_avar_mappings(avar, fixed_coords, |coord| *coord, core::convert::identity);

Expand All @@ -170,14 +159,9 @@ impl<'a> Fvar<'a> {
let var_store = avar.var_store();
let var_index_map = avar.axis_index_map();

let mut stack_coords_2dot14 = [F2Dot14::ZERO; MAX_INLINE_AVAR2_AXES];
let mut heap_coords_2dot14 = Vec::new();
let coords_2dot14 = if actual_len > MAX_INLINE_AVAR2_AXES {
heap_coords_2dot14.resize(actual_len, F2Dot14::ZERO);
heap_coords_2dot14.as_mut_slice()
} else {
&mut stack_coords_2dot14[..actual_len]
};
let mut coords_2dot14 =
SmallVec::<[F2Dot14; MAX_INLINE_AVAR2_AXES]>::from_elem(F2Dot14::ZERO, actual_len);
let coords_2dot14 = coords_2dot14.as_mut_slice();
for (coord_2dot14, coord) in coords_2dot14.iter_mut().zip(fixed_coords.iter()) {
*coord_2dot14 = coord.to_f2dot14();
}
Expand Down
1 change: 1 addition & 0 deletions skrifa/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@ spec_next = ["read-fonts/spec_next"]
libm = ["dep:core_maths", "read-fonts/libm"]

[dependencies]
smallvec = { workspace = true }
read-fonts = { workspace = true, default-features = false }
core_maths = { workspace = true, optional = true }
bytemuck = { workspace = true }
Expand Down
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