harfrust/hb/ot/gsub/
alternate.rs

1use crate::hb::ot_layout_gsubgpos::OT::hb_ot_apply_context_t;
2use crate::hb::ot_layout_gsubgpos::{Apply, WouldApply, WouldApplyContext};
3use read_fonts::tables::gsub::{AlternateSet, AlternateSubstFormat1};
4
5impl Apply for AlternateSet<'_> {
6    fn apply(&self, ctx: &mut hb_ot_apply_context_t) -> Option<()> {
7        let alternates = self.alternate_glyph_ids();
8        let len = alternates.len() as u16;
9        if len == 0 {
10            return None;
11        }
12
13        let glyph_mask = ctx.buffer.cur(0).mask;
14
15        // Note: This breaks badly if two features enabled this lookup together.
16        let shift = ctx.lookup_mask().trailing_zeros();
17        let mut alt_index = (ctx.lookup_mask() & glyph_mask) >> shift;
18
19        // If alt_index is MAX_VALUE, randomize feature if it is the rand feature.
20        if alt_index == crate::hb::ot_map::hb_ot_map_t::MAX_VALUE && ctx.random {
21            // Maybe we can do better than unsafe-to-break all; but since we are
22            // changing random state, it would be hard to track that.  Good 'nough.
23            ctx.buffer.unsafe_to_break(Some(0), Some(ctx.buffer.len));
24            alt_index = ctx.random_number() % u32::from(len) + 1;
25        }
26
27        let idx = u16::try_from(alt_index).ok()?.checked_sub(1)?;
28        ctx.replace_glyph(alternates.get(idx as usize)?.get().into());
29
30        Some(())
31    }
32}
33
34impl WouldApply for AlternateSubstFormat1<'_> {
35    fn would_apply(&self, ctx: &WouldApplyContext) -> bool {
36        ctx.glyphs.len() == 1
37            && self
38                .coverage()
39                .is_ok_and(|cov| cov.get(ctx.glyphs[0]).is_some())
40    }
41}
42
43impl Apply for AlternateSubstFormat1<'_> {
44    fn apply(&self, ctx: &mut hb_ot_apply_context_t) -> Option<()> {
45        let glyph = ctx.buffer.cur(0).as_glyph();
46        let index = self.coverage().ok()?.get(glyph)?;
47        let set = self.alternate_sets().get(index as usize).ok()?;
48        set.apply(ctx)
49    }
50}
harfrust/hb/ot/gsub/alternate.rs

harfrust/hb/ot/gsub/
alternate.rs
