1use crate::hb::ot_layout_gsubgpos::Apply;
2use crate::hb::ot_layout_gsubgpos::OT::hb_ot_apply_context_t;
3use crate::hb::ot_map::hb_ot_map_t;
4use core::convert::TryFrom;
5use ttf_parser::gsub::AlternateSet;
6
7impl Apply for AlternateSet<'_> {
8 fn apply(&self, ctx: &mut hb_ot_apply_context_t) -> Option<()> {
9 let len = self.alternates.len();
10 if len == 0 {
11 return None;
12 }
13
14 let glyph_mask = ctx.buffer.cur(0).mask;
15
16 // Note: This breaks badly if two features enabled this lookup together.
17 let shift = ctx.lookup_mask().trailing_zeros();
18 let mut alt_index = (ctx.lookup_mask() & glyph_mask) >> shift;
19
20 // If alt_index is MAX_VALUE, randomize feature if it is the rand feature.
21 if alt_index == hb_ot_map_t::MAX_VALUE && ctx.random {
22 // Maybe we can do better than unsafe-to-break all; but since we are
23 // changing random state, it would be hard to track that. Good 'nough.
24 ctx.buffer.unsafe_to_break(Some(0), Some(ctx.buffer.len));
25 alt_index = ctx.random_number() % u32::from(len) + 1;
26 }
27
28 let idx = u16::try_from(alt_index).ok()?.checked_sub(1)?;
29 ctx.replace_glyph(self.alternates.get(idx)?);
30
31 Some(())
32 }
33}
34