Cache rustybuzz shape plans.

src/shape_plan_cache.rs

@@ -0,0 +1,52 @@
+use std::collections::hash_map::Entry;
+
+use crate::{Font, HashMap};
+
+/// Key for caching shape plans.
+#[derive(Debug, Hash, PartialEq, Eq)]
+struct ShapePlanKey {
+    font_id: fontdb::ID,
+    direction: rustybuzz::Direction,
+    script: rustybuzz::Script,
+    language: Option<rustybuzz::Language>,
+}
+
+/// A helper structure for caching rustybuzz shape plans.
+#[derive(Default)]
+pub struct ShapePlanCache(HashMap<ShapePlanKey, rustybuzz::ShapePlan>);
+
+impl ShapePlanCache {
+    pub fn get(&mut self, font: &Font, buffer: &rustybuzz::UnicodeBuffer) -> &rustybuzz::ShapePlan {
+        let key = ShapePlanKey {
+            font_id: font.id(),
+            direction: buffer.direction(),
+            script: buffer.script(),
+            language: buffer.language(),
+        };
+        match self.0.entry(key) {
+            Entry::Occupied(occ) => occ.into_mut(),
+            Entry::Vacant(vac) => {
+                let ShapePlanKey {
+                    direction,
+                    script,
+                    language,
+                    ..
+                } = vac.key();
+                let plan = rustybuzz::ShapePlan::new(
+                    font.rustybuzz(),
+                    *direction,
+                    Some(*script),
+                    language.as_ref(),
+                    &[],
+                );
+                vac.insert(plan)
+            }
+        }
+    }
+}
+
+impl std::fmt::Debug for ShapePlanCache {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_tuple("ShapePlanCache").finish()
+    }
+}