Add caching of swash rendering, significantly improves layout speed

examples/text/src/font/mod.rs

@@ -1,3 +1,11 @@
+use std::{
+    collections::HashMap,
+    sync::Mutex,
+};
+
+pub use self::cache::*;
+mod cache;
+
 pub use self::layout::*;
 mod layout;
 
@@ -10,6 +18,12 @@ mod shape;
 pub use self::system::*;
 mod system;
 
+#[derive(Clone, Copy, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub struct FontCacheKey {
+    glyph_id: u16,
+
+}
+
 #[derive(Clone, Copy, Eq, PartialEq, Ord, PartialOrd)]
 pub struct FontLineIndex(usize);
 
@@ -32,6 +46,9 @@ pub struct Font<'a> {
     pub rusttype: rusttype::Font<'a>,
     #[cfg(feature = "swash")]
     pub swash: swash::FontRef<'a>,
+    #[cfg(feature = "swash")]
+    pub scale_context: Mutex<swash::scale::ScaleContext>,
+    pub cache: Mutex<HashMap<CacheKey, CacheItem>>,
 }
 
 impl<'a> Font<'a> {
@@ -45,6 +62,9 @@ impl<'a> Font<'a> {
             rusttype: rusttype::Font::try_from_bytes_and_index(data, index)?,
             #[cfg(feature = "swash")]
             swash: swash::FontRef::from_index(data, index as usize)?,
+            #[cfg(feature = "swash")]
+            scale_context: Mutex::new(swash::scale::ScaleContext::new()),
+            cache: Mutex::new(HashMap::new()),
         })
     }
 }