From f5879b3425f39d6d6a442642bcd66986b6554487 Mon Sep 17 00:00:00 2001
From: Stewart Connor <stewart@canva.com>
Date: Fri, 21 Mar 2025 18:24:32 +1100
Subject: [PATCH] add contextual alternatives

---
 src/attrs.rs | 3 +++
 src/shape.rs | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/src/attrs.rs b/src/attrs.rs
index c9ca70e..c13642e 100644
--- a/src/attrs.rs
+++ b/src/attrs.rs
@@ -134,6 +134,8 @@ pub struct FontFeatures {
     pub standard_ligatures: bool,
     /// Contextual ligatures (context-dependent ligatures)
     pub contextual_ligatures: bool,
+    /// Contextual alternates (glyph substitutions based on context)
+    pub contextual_alternates: bool,
     /// Discretionary ligatures (optional stylistic ligatures)
     pub discretionary_ligatures: bool,
 }
@@ -145,6 +147,7 @@ impl FontFeatures {
             kerning: true,
             standard_ligatures: true,
             contextual_ligatures: true,
+            contextual_alternates: true,
             discretionary_ligatures: true,
         }
     }
diff --git a/src/shape.rs b/src/shape.rs
index 21752cb..a6c400d 100644
--- a/src/shape.rs
+++ b/src/shape.rs
@@ -158,6 +158,11 @@ fn shape_fallback(
         attrs.font_features.contextual_ligatures as u32,
         0..usize::MAX,
     ));
+    features.push(rustybuzz::Feature::new(
+        rustybuzz::ttf_parser::Tag::from_bytes(b"calt"),
+        attrs.font_features.contextual_alternates as u32,
+        0..usize::MAX,
+    ));
     features.push(rustybuzz::Feature::new(
         rustybuzz::ttf_parser::Tag::from_bytes(b"dlig"),
         attrs.font_features.discretionary_ligatures as u32,