Add shape-run-cache feature, that can significantly improve shaping performance

src/shape_run_cache.rs

@@ -0,0 +1,49 @@
+#[cfg(not(feature = "std"))]
+use alloc::{string::String, vec::Vec};
+use core::ops::Range;
+
+use crate::{AttrsOwned, HashMap, ShapeGlyph};
+
+/// Key for caching shape runs.
+#[derive(Clone, Debug, Hash, PartialEq, Eq)]
+pub struct ShapeRunKey {
+    pub text: String,
+    pub default_attrs: AttrsOwned,
+    pub attrs_spans: Vec<(Range<usize>, AttrsOwned)>,
+}
+
+/// A helper structure for caching shape runs.
+#[derive(Clone, Default)]
+pub struct ShapeRunCache {
+    age: u64,
+    cache: HashMap<ShapeRunKey, (u64, Vec<ShapeGlyph>)>,
+}
+
+impl ShapeRunCache {
+    /// Get cache item, updating age if found
+    pub fn get(&mut self, key: &ShapeRunKey) -> Option<&Vec<ShapeGlyph>> {
+        self.cache.get_mut(key).map(|(age, glyphs)| {
+            *age = self.age;
+            &*glyphs
+        })
+    }
+
+    /// Insert cache item with current age
+    pub fn insert(&mut self, key: ShapeRunKey, glyphs: Vec<ShapeGlyph>) {
+        self.cache.insert(key, (self.age, glyphs));
+    }
+
+    /// Remove anything in the cache with an age older than keep_ages
+    pub fn trim(&mut self, keep_ages: u64) {
+        self.cache
+            .retain(|_key, (age, _glyphs)| *age + keep_ages >= self.age);
+        // Increase age
+        self.age += 1;
+    }
+}
+
+impl core::fmt::Debug for ShapeRunCache {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_tuple("ShapeRunCache").finish()
+    }
+}