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//! An [Index to Location Table](https://docs.microsoft.com/en-us/typography/opentype/spec/loca)
//! implementation.
use core::num::NonZeroU16;
use core::ops::Range;
use crate::{GlyphId, IndexToLocationFormat};
use crate::parser::{Stream, LazyArray16, NumFrom};
/// An [Index to Location Table](https://docs.microsoft.com/en-us/typography/opentype/spec/loca).
#[derive(Clone, Copy, Debug)]
pub enum Table<'a> {
/// Short offsets.
Short(LazyArray16<'a, u16>),
/// Long offsets.
Long(LazyArray16<'a, u32>),
}
impl<'a> Table<'a> {
/// Parses a table from raw data.
///
/// - `number_of_glyphs` is from the `maxp` table.
/// - `format` is from the `head` table.
pub fn parse(
number_of_glyphs: NonZeroU16,
format: IndexToLocationFormat,
data: &'a [u8],
) -> Option<Self> {
// The number of ranges is `maxp.numGlyphs + 1`.
//
// Check for overflow first.
let total = if number_of_glyphs.get() == core::u16::MAX {
number_of_glyphs.get()
} else {
number_of_glyphs.get() + 1
};
let mut s = Stream::new(data);
match format {
IndexToLocationFormat::Short => {
Some(Table::Short(s.read_array16::<u16>(total)?))
}
IndexToLocationFormat::Long => {
Some(Table::Long(s.read_array16::<u32>(total)?))
}
}
}
/// Returns offsets length.
#[inline]
pub fn len(&self) -> u16 {
match self {
Table::Short(ref array) => array.len(),
Table::Long(ref array) => array.len(),
}
}
/// Returns glyph's range in the `glyf` table.
#[inline]
pub fn glyph_range(&self, glyph_id: GlyphId) -> Option<Range<usize>> {
let glyph_id = glyph_id.0;
if glyph_id == core::u16::MAX {
return None;
}
// Glyph ID must be smaller than total number of values in a `loca` array.
if glyph_id + 1 >= self.len() {
return None;
}
let range = match self {
Table::Short(ref array) => {
// 'The actual local offset divided by 2 is stored.'
usize::from(array.get(glyph_id)?) * 2 .. usize::from(array.get(glyph_id + 1)?) * 2
}
Table::Long(ref array) => {
usize::num_from(array.get(glyph_id)?) .. usize::num_from(array.get(glyph_id + 1)?)
}
};
if range.start >= range.end {
// 'The offsets must be in ascending order.'
// And range cannot be empty.
None
} else {
Some(range)
}
}
}