126 lines
3.9 KiB
Rust
126 lines
3.9 KiB
Rust
//! A [Horizontal/Vertical Metrics Variations Table](
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//! https://docs.microsoft.com/en-us/typography/opentype/spec/hvar) implementation.
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use core::convert::TryFrom;
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use crate::{GlyphId, NormalizedCoordinate};
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use crate::parser::{Stream, Offset, Offset32};
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use crate::var_store::ItemVariationStore;
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struct DeltaSetIndexMap<'a> {
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data: &'a [u8],
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}
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impl<'a> DeltaSetIndexMap<'a> {
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#[inline]
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fn new(data: &'a [u8]) -> Self {
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DeltaSetIndexMap { data }
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}
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#[inline]
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fn map(&self, glyph_id: GlyphId) -> Option<(u16, u16)> {
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let mut idx = glyph_id.0;
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let mut s = Stream::new(self.data);
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let entry_format = s.read::<u16>()?;
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let map_count = s.read::<u16>()?;
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if map_count == 0 {
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return None;
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}
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// 'If a given glyph ID is greater than mapCount-1, then the last entry is used.'
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if idx >= map_count {
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idx = map_count - 1;
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}
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let entry_size = ((entry_format >> 4) & 3) + 1;
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let inner_index_bit_count = u32::from((entry_format & 0xF) + 1);
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s.advance(usize::from(entry_size) * usize::from(idx));
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let mut n = 0u32;
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for b in s.read_bytes(usize::from(entry_size))? {
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n = (n << 8) + u32::from(*b);
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}
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let outer_index = n >> inner_index_bit_count;
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let inner_index = n & ((1 << inner_index_bit_count) - 1);
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Some((
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u16::try_from(outer_index).ok()?,
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u16::try_from(inner_index).ok()?
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))
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}
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}
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/// A [Horizontal/Vertical Metrics Variations Table](
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/// https://docs.microsoft.com/en-us/typography/opentype/spec/hvar).
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#[derive(Clone, Copy)]
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pub struct Table<'a> {
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data: &'a [u8],
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variation_store: ItemVariationStore<'a>,
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advance_width_mapping_offset: Option<Offset32>,
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lsb_mapping_offset: Option<Offset32>,
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}
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impl<'a> Table<'a> {
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/// Parses a table from raw data.
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pub fn parse(data: &'a [u8]) -> Option<Self> {
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let mut s = Stream::new(data);
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let version = s.read::<u32>()?;
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if version != 0x00010000 {
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return None;
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}
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let variation_store_offset = s.read::<Offset32>()?;
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let var_store_s = Stream::new_at(data, variation_store_offset.to_usize())?;
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let variation_store = ItemVariationStore::parse(var_store_s)?;
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Some(Table {
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data,
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variation_store,
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advance_width_mapping_offset: s.read::<Option<Offset32>>()?,
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lsb_mapping_offset: s.read::<Option<Offset32>>()?,
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})
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}
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/// Returns advance offset for a glyph.
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#[inline]
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pub fn advance_offset(
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&self,
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glyph_id: GlyphId,
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coordinates: &[NormalizedCoordinate],
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) -> Option<f32> {
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let (outer_idx, inner_idx) = if let Some(offset) = self.advance_width_mapping_offset {
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DeltaSetIndexMap::new(self.data.get(offset.to_usize()..)?).map(glyph_id)?
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} else {
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// 'If there is no delta-set index mapping table for advance widths,
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// then glyph IDs implicitly provide the indices:
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// for a given glyph ID, the delta-set outer-level index is zero,
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// and the glyph ID is the delta-set inner-level index.'
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(0, glyph_id.0)
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};
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self.variation_store.parse_delta(outer_idx, inner_idx, coordinates)
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}
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/// Returns side bearing offset for a glyph.
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#[inline]
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pub fn side_bearing_offset(
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&self,
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glyph_id: GlyphId,
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coordinates: &[NormalizedCoordinate],
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) -> Option<f32> {
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let set_data = self.data.get(self.lsb_mapping_offset?.to_usize()..)?;
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let (outer_idx, inner_idx) = DeltaSetIndexMap::new(set_data).map(glyph_id)?;
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self.variation_store.parse_delta(outer_idx, inner_idx, coordinates)
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}
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}
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impl core::fmt::Debug for Table<'_> {
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fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
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write!(f, "Table {{ ... }}")
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}
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}
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