1 files changed, 115 insertions, 0 deletions
diff --git a/gfx/wr/webrender_api/src/display_item_cache.rs b/gfx/wr/webrender_api/src/display_item_cache.rs
new file mode 100644
index 0000000000..6cd1eb3e3a
--- /dev/null
+++ b/gfx/wr/webrender_api/src/display_item_cache.rs
@@ -0,0 +1,115 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::display_item::*;
+use crate::display_list::*;
+use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
+
+#[derive(Clone, Debug, Deserialize, PartialEq, Serialize)]
+pub struct CachedDisplayItem {
+    item: DisplayItem,
+    data: Vec<u8>,
+}
+
+impl CachedDisplayItem {
+    pub fn display_item(&self) -> &DisplayItem {
+        &self.item
+    }
+
+    pub fn data_as_item_range<T>(&self) -> ItemRange<T> {
+        ItemRange::new(&self.data)
+    }
+}
+
+impl MallocSizeOf for CachedDisplayItem {
+    fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
+        self.data.size_of(ops)
+    }
+}
+
+impl From<DisplayItemRef<'_, '_>> for CachedDisplayItem {
+    fn from(item_ref: DisplayItemRef) -> Self {
+        let item = item_ref.item();
+
+        match item {
+            DisplayItem::Text(..) => CachedDisplayItem {
+                item: *item,
+                data: item_ref.glyphs().bytes().to_vec(),
+            },
+            _ => CachedDisplayItem {
+                item: *item,
+                data: Vec::new(),
+            },
+        }
+    }
+}
+
+#[derive(Clone, Deserialize, MallocSizeOf, Serialize)]
+struct CacheEntry {
+    items: Vec<CachedDisplayItem>,
+    occupied: bool,
+}
+
+#[derive(Clone, Deserialize, MallocSizeOf, Serialize)]
+pub struct DisplayItemCache {
+    entries: Vec<CacheEntry>,
+}
+
+impl DisplayItemCache {
+    fn add_item(&mut self, key: ItemKey, item: CachedDisplayItem) {
+        let mut entry = &mut self.entries[key as usize];
+        entry.items.push(item);
+        entry.occupied = true;
+    }
+
+    fn clear_entry(&mut self, key: ItemKey) {
+        let mut entry = &mut self.entries[key as usize];
+        entry.items.clear();
+        entry.occupied = false;
+    }
+
+    fn grow_if_needed(&mut self, capacity: usize) {
+        if capacity > self.entries.len() {
+            self.entries.resize_with(capacity, || CacheEntry {
+                items: Vec::new(),
+                occupied: false,
+            });
+        }
+    }
+
+    pub fn get_items(&self, key: ItemKey) -> &[CachedDisplayItem] {
+        let entry = &self.entries[key as usize];
+        debug_assert!(entry.occupied);
+        entry.items.as_slice()
+    }
+
+    pub fn new() -> Self {
+        Self {
+            entries: Vec::new(),
+        }
+    }
+
+    pub fn update(&mut self, display_list: &BuiltDisplayList) {
+        self.grow_if_needed(display_list.cache_size());
+
+        let mut iter = display_list.cache_data_iter();
+        let mut current_key: Option<ItemKey> = None;
+        loop {
+            let item = match iter.next() {
+                Some(item) => item,
+                None => break,
+            };
+
+            if let DisplayItem::RetainedItems(key) = item.item() {
+                current_key = Some(*key);
+                self.clear_entry(*key);
+                continue;
+            }
+
+            let key = current_key.expect("Missing RetainedItems marker");
+            let cached_item = CachedDisplayItem::from(item);
+            self.add_item(key, cached_item);
+        }
+    }
+}