106 lines
3.4 KiB
Rust
106 lines
3.4 KiB
Rust
//! An [Index to Location Table](https://docs.microsoft.com/en-us/typography/opentype/spec/loca)
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//! implementation.
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use core::convert::TryFrom;
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use core::num::NonZeroU16;
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use core::ops::Range;
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use crate::parser::{LazyArray16, NumFrom, Stream};
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use crate::{GlyphId, IndexToLocationFormat};
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/// An [Index to Location Table](https://docs.microsoft.com/en-us/typography/opentype/spec/loca).
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#[derive(Clone, Copy, Debug)]
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pub enum Table<'a> {
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/// Short offsets.
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Short(LazyArray16<'a, u16>),
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/// Long offsets.
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Long(LazyArray16<'a, u32>),
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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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///
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/// - `number_of_glyphs` is from the `maxp` table.
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/// - `format` is from the `head` table.
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pub fn parse(
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number_of_glyphs: NonZeroU16,
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format: IndexToLocationFormat,
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data: &'a [u8],
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) -> Option<Self> {
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// The number of ranges is `maxp.numGlyphs + 1`.
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//
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// Check for overflow first.
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let mut total = if number_of_glyphs.get() == core::u16::MAX {
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number_of_glyphs.get()
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} else {
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number_of_glyphs.get() + 1
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};
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// By the spec, the number of `loca` offsets is `maxp.numGlyphs + 1`.
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// But some malformed fonts can have less glyphs than that.
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// In which case we try to parse only the available offsets
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// and do not return an error, since the expected data length
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// would go beyond table's length.
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//
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// In case when `loca` has more data than needed we simply ignore the rest.
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let actual_total = match format {
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IndexToLocationFormat::Short => data.len() / 2,
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IndexToLocationFormat::Long => data.len() / 4,
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};
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let actual_total = u16::try_from(actual_total).ok()?;
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total = total.min(actual_total);
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let mut s = Stream::new(data);
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match format {
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IndexToLocationFormat::Short => Some(Table::Short(s.read_array16::<u16>(total)?)),
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IndexToLocationFormat::Long => Some(Table::Long(s.read_array16::<u32>(total)?)),
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}
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}
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/// Returns the number of offsets.
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#[inline]
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pub fn len(&self) -> u16 {
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match self {
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Table::Short(ref array) => array.len(),
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Table::Long(ref array) => array.len(),
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}
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}
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/// Checks if there are any offsets.
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pub fn is_empty(&self) -> bool {
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self.len() == 0
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}
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/// Returns glyph's range in the `glyf` table.
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#[inline]
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pub fn glyph_range(&self, glyph_id: GlyphId) -> Option<Range<usize>> {
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let glyph_id = glyph_id.0;
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if glyph_id == core::u16::MAX {
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return None;
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}
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// Glyph ID must be smaller than total number of values in a `loca` array.
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if glyph_id + 1 >= self.len() {
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return None;
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}
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let range = match self {
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Table::Short(ref array) => {
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// 'The actual local offset divided by 2 is stored.'
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usize::from(array.get(glyph_id)?) * 2..usize::from(array.get(glyph_id + 1)?) * 2
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}
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Table::Long(ref array) => {
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usize::num_from(array.get(glyph_id)?)..usize::num_from(array.get(glyph_id + 1)?)
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}
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};
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if range.start >= range.end {
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// 'The offsets must be in ascending order.'
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// And range cannot be empty.
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None
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} else {
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Some(range)
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}
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}
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}
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