From 31da676415e2022c1cd417d4d3b395148742e01f Mon Sep 17 00:00:00 2001
From: FredApps <153173854+FredApps@users.noreply.github.com>
Date: Tue, 10 Nov 2026 13:10:10 +0100
Subject: [PATCH] #2104: bound audio comparisons across reused precomps

---
 crates/ui-egui/src/audio.rs            | 18 +++++++++++------
 crates/ui-egui/src/audio/live_tests.rs | 28 ++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/crates/ui-egui/src/audio.rs b/crates/ui-egui/src/audio.rs
index 015794305..a8cb54d6d 100644
--- a/crates/ui-egui/src/audio.rs
+++ b/crates/ui-egui/src/audio.rs
@@ -18,7 +18,7 @@
 //! **Scrubbing:** Ctrl/Cmd-dragging the current-time indicator plays a short snippet of the mix
 //! at each new frame ([`AudioScrub`], `playback.scrubAudio`), as in After Effects.
 
-use std::collections::VecDeque;
+use std::collections::{HashSet, VecDeque};
 use std::sync::atomic::{AtomicBool, AtomicU32, AtomicU64, Ordering};
 use std::sync::{Arc, Mutex};
 use std::thread::JoinHandle;
@@ -338,11 +338,17 @@ impl Drop for AudioPlayback {
 /// Effects switch, Audio Levels or effects, or the same for a nested comp. Other edits (video
 /// properties, names, labels) do not change the mix unless an audio expression can read them.
 fn audio_changed(old: &Project, new: &Project, comp: ItemId) -> bool {
-    fn comps_differ(old: &Project, new: &Project, comp: ItemId, depth: usize) -> bool {
-        let (Some(a), Some(b)) = (old.comp(comp), new.comp(comp)) else { return old.comp(comp).is_some() != new.comp(comp).is_some() };
-        if depth >= 16 {
+    audio_changed_inner(old, new, comp, &mut HashSet::new())
+}
+
+/// Each shared precomp is compared once per depth. A depth limit alone still visits an
+/// exponentially large number of paths in a small graph of reused precomps, blocking the UI.
+fn audio_changed_inner(old: &Project, new: &Project, comp: ItemId, seen: &mut HashSet<(ItemId, usize)>) -> bool {
+    fn comps_differ(old: &Project, new: &Project, comp: ItemId, depth: usize, seen: &mut HashSet<(ItemId, usize)>) -> bool {
+        if depth >= 16 || !seen.insert((comp, depth)) {
             return false;
         }
+        let (Some(a), Some(b)) = (old.comp(comp), new.comp(comp)) else { return old.comp(comp).is_some() != new.comp(comp).is_some() };
         a.layers.len() != b.layers.len()
             || a.layers.iter().zip(&b.layers).any(|(x, y)| {
                 x.id != y.id
@@ -360,7 +366,7 @@ fn audio_changed(old: &Project, new: &Project, comp: ItemId) -> bool {
                     || audio_has_expression(y)
                     || match &x.source {
                         LayerSource::Footage { item } => footage_differs(old, new, *item),
-                        LayerSource::Comp { item } => comps_differ(old, new, *item, depth + 1),
+                        LayerSource::Comp { item } => comps_differ(old, new, *item, depth + 1, seen),
                         _ => false,
                     }
             })
@@ -386,7 +392,7 @@ fn audio_changed(old: &Project, new: &Project, comp: ItemId) -> bool {
         };
         f(old) != f(new)
     }
-    comps_differ(old, new, comp, 0)
+    comps_differ(old, new, comp, 0, seen)
 }
 
 /// Mix one block at the feeder's cursor into the feed and move the cursor on (wrapping or
diff --git a/crates/ui-egui/src/audio/live_tests.rs b/crates/ui-egui/src/audio/live_tests.rs
index 6be2909cd..28ea3be3e 100644
--- a/crates/ui-egui/src/audio/live_tests.rs
+++ b/crates/ui-egui/src/audio/live_tests.rs
@@ -179,3 +179,31 @@ fn video_edits_keep_the_queue_unless_audio_expressions_can_read_them() {
         }
     }
 }
+
+#[test]
+fn shared_nested_comps_are_compared_once_per_depth() {
+    let mut project = Project::default();
+    let mut child = None;
+    for _ in 0..10 {
+        let mut comp = Comp::new(64, 36, FrameRate::new(30, 1), Tick::from_seconds_f64(1.0));
+        if let Some(item) = child {
+            for _ in 0..10 {
+                let mut layer = build::layer(&mut project, &comp, "Nested", LayerSource::Comp { item }, (64, 36), None);
+                layer.switches.audio = false;
+                comp.layers.push(layer);
+            }
+        }
+        child = Some(project.add_item("Nested", Label::Sandstone, None, ItemKind::Comp(comp.into())));
+    }
+    let root = child.unwrap();
+    let mut edited = project.clone();
+    edited.comp_mut(root).unwrap().layers[0].name = "Renamed".into();
+    let mut seen = std::collections::HashSet::new();
+    assert!(!super::audio_changed_inner(&project, &edited, root, &mut seen));
+    assert_eq!(seen.len(), 10, "compare the ten comps, not a billion paths through them");
+    let leaf = *seen.iter().find(|(_, depth)| *depth == 9).map(|(item, _)| item).unwrap();
+    let mut layer = project.comp(root).unwrap().layers[0].clone();
+    layer.source = LayerSource::Null;
+    edited.comp_mut(leaf).unwrap().layers.push(layer);
+    assert!(super::audio_changed(&project, &edited, root), "memoization must still find a nested edit");
+}