Levels

2 files changed, 28 insertions, 7 deletions

diff --git a/src/layout/incremental.rs b/src/layout/incremental.rs
index 427df079..7857f33c 100644
--- a/src/layout/incremental.rs
+++ b/src/layout/incremental.rs
@@ -20,6 +20,19 @@ impl LayoutCache {
     pub fn clear(&mut self) {
         self.frames.clear();
     }
+
+    /// Retains all elements for which the closure on the level returns `true`.
+    pub fn retain<F>(&mut self, mut f: F)
+    where
+        F: FnMut(usize) -> bool,
+    {
+        self.frames.retain(|_, b| f(b.level));
+    }
+
+    /// Amount of items in the cache.
+    pub fn len(&self) -> usize {
+        self.frames.len()
+    }
 }
 
 #[derive(Debug, Clone)]
@@ -27,6 +40,8 @@ impl LayoutCache {
 pub struct FramesEntry {
     /// The cached frames for a node.
     pub frames: Vec<Constrained<Frame>>,
+    /// How nested the frame was in the context is was originally appearing in.
+    pub level: usize,
 }
 
 impl FramesEntry {
diff --git a/src/layout/mod.rs b/src/layout/mod.rs
index 15c80017..28e83da9 100644
--- a/src/layout/mod.rs
+++ b/src/layout/mod.rs
@@ -32,7 +32,7 @@ use crate::loading::Loader;
 
 /// Layout a tree into a collection of frames.
 pub fn layout(loader: &mut dyn Loader, cache: &mut Cache, tree: &Tree) -> Vec<Frame> {
-    tree.layout(&mut LayoutContext { loader, cache })
+    tree.layout(&mut LayoutContext { loader, cache, level: 0 })
 }
 
 /// A tree of layout nodes.
@@ -98,19 +98,23 @@ impl Layout for AnyNode {
         ctx: &mut LayoutContext,
         regions: &Regions,
     ) -> Vec<Constrained<Frame>> {
-        ctx.cache
+        ctx.level += 1;
+        let frames = ctx
+            .cache
             .layout
             .frames
             .get(&self.hash)
             .and_then(|x| x.check(regions.clone()))
             .unwrap_or_else(|| {
                 let frames = self.node.layout(ctx, regions);
-                ctx.cache
-                    .layout
-                    .frames
-                    .insert(self.hash, FramesEntry { frames: frames.clone() });
+                ctx.cache.layout.frames.insert(self.hash, FramesEntry {
+                    frames: frames.clone(),
+                    level: ctx.level - 1,
+                });
                 frames
-            })
+            });
+        ctx.level -= 1;
+        frames
     }
 }
 
@@ -184,6 +188,8 @@ pub struct LayoutContext<'a> {
     pub loader: &'a mut dyn Loader,
     /// A cache for loaded fonts and artifacts from past layouting.
     pub cache: &'a mut Cache,
+    /// How deeply nested is the current layout tree position.
+    pub level: usize,
 }
 
 /// A sequence of regions to layout into.