Merge pull request #2562 from tylerjenningsw/enhance/audio-levels-link

Audio: link stereo level edits while preserving channel balance

crates/engine/src/cmd/prop.rs

@@ -286,8 +286,13 @@ fn twin_params(p: &Value, lid: LayerId, uid: Uid) -> Value {
 /// The value of property `uid` of `lid` at the CTI as numbers (Position with Separate
 /// Dimensions: its X / Y / Z Position).
 fn current_components(s: &Session, cid: ItemId, lid: LayerId, uid: Uid) -> Option<Vec<f64>> {
+    components_at(s, cid, lid, uid, None)
+}
+
+/// [`current_components`] at layer time `at` (the CTI when `None`).
+fn components_at(s: &Session, cid: ItemId, lid: LayerId, uid: Uid, at: Option<Tick>) -> Option<Vec<f64>> {
     let l = s.project.comp(cid)?.layer(lid)?;
-    let lt = l.layer_time(s.time_of(cid));
+    let lt = at.unwrap_or_else(|| l.layer_time(s.time_of(cid)));
     if let Some(tr) = l.transform()
         && tr.get("position").is_some_and(|q| q.uid == uid)
         && tr.get("positionX").is_some()
@@ -319,7 +324,9 @@ pub(crate) fn proportional_share(index: usize, count: usize) -> f64 {
 /// `prop.set`; with `selected`, also on the other selected layers: the same value, or with
 /// `offset` (a scrub) the same change from each layer's own value. A typed value with `dims`
 /// (the components edited, e.g. `[2]` for Z) sets only those components on the other layers,
-/// which keep the rest of their own value (#1434). With `offset` and
+/// which keep the rest of their own value (#1434); `follow` components move on each layer by the
+/// change its first typed component takes (linked Audio Levels keep each layer's balance, #2485).
+/// With `offset` and
 /// `proportional` (Proportional Scrubbing) each layer takes [`proportional_share`] of the change
 /// by its place in the selection order, the scrubbed layer too. One undo step (with `merge`,
 /// one that a continuing scrub keeps folding into).
@@ -344,10 +351,19 @@ fn set_selected(s: &mut Session, p: &Value) -> Result<Value> {
         (None, Some(a), Some(_)) if !scalar => Some(a.iter().filter_map(Value::as_u64).filter_map(|d| usize::try_from(d).ok()).collect()),
         _ => None,
     };
+    let follow: Vec<usize> =
+        p.get("follow").and_then(Value::as_array).into_iter().flatten().filter_map(Value::as_u64).filter_map(|d| usize::try_from(d).ok()).collect();
+    // Each layer's own value where `set` writes it (a `time` other than the CTI keys there).
     let typed = |s: &Session, q: &mut Value, olid: LayerId, ouid: Uid| {
         if let (Some(dims), Some(n)) = (&dims, &new)
-            && let Some(mut c) = current_components(s, cid, olid, ouid)
+            && let Some(mut c) = components_at(s, cid, olid, ouid, snapped_key_time(s, cid, olid, q, "prop.set").ok().flatten())
         {
+            let change = dims.first().and_then(|&d| Some(n.get(d)? - c.get(d)?)).unwrap_or(0.0);
+            for &d in &follow {
+                if let Some(slot) = c.get_mut(d) {
+                    *slot += change;
+                }
+            }
             for &d in dims {
                 if let (Some(slot), Some(v)) = (c.get_mut(d), n.get(d)) {
                     *slot = *v;
@@ -1388,7 +1404,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Set Property Value",
             [],
             None,
-            "{layer?, path|prop, value, time? (layer s by default), timeBase?: layer|comp, merge?, selected? (also the other selected layers), offset? (them by the same change), proportional? (with offset: Proportional Scrubbing, each layer by its share in selection order, the first none, the last all), dims? (with selected, a typed value: the components edited, e.g. [2] for Z; the other layers keep the rest of their own value)}",
+            "{layer?, path|prop, value, time? (layer s by default), timeBase?: layer|comp, merge?, selected? (also the other selected layers), offset? (them by the same change), proportional? (with offset: Proportional Scrubbing, each layer by its share in selection order, the first none, the last all), dims? (with selected, a typed value: the components edited, e.g. [2] for Z; the other layers keep the rest of their own value), follow? (with dims: components that move on each other layer by the change its first typed component takes)}",
             has_layers,
             set_selected
         ),

crates/engine/src/tests/timeline.rs

@@ -1530,3 +1530,29 @@ fn a_typed_component_applies_only_that_component_to_the_selected_layers() {
     s.execute("prop.set", json!({"layer": a, "prop": uid, "value": [1.0, 2.0, 3.0], "selected": true})).unwrap();
     assert_eq!(pos(&s, c), vec![1.0, 2.0, 3.0]);
 }
+
+/// #2485: linked Audio Levels typed with several layers selected: each takes the typed Left, and
+/// its Right moves by its own change, so every layer keeps its own stereo balance.
+#[test]
+fn a_typed_component_moves_its_follow_components_by_each_layers_own_change() {
+    let mut s = Session::default();
+    s.execute("comp.new", json!({"name": "Sound", "width": 64, "height": 36, "duration": 4})).unwrap();
+    s.execute("comp.new", json!({"name": "Main", "width": 320, "height": 180, "duration": 4})).unwrap();
+    let a = s.execute("layer.addItem", json!({"item": "Sound"})).unwrap()["layer"].as_u64().unwrap();
+    let b = s.execute("layer.addItem", json!({"item": "Sound"})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("prop.set", json!({"layer": a, "path": "audio/levels", "value": [-6.0, -12.0]})).unwrap();
+    s.execute("prop.set", json!({"layer": b, "path": "audio/levels", "value": [-20.0, -30.0]})).unwrap();
+    s.execute("layer.select", json!({"layers": [a, b]})).unwrap();
+    let uid = prop(&s, a, "audio/levels").uid;
+    let undo = s.history.undo.len();
+    s.execute_checked("prop.set", json!({"layer": a, "prop": uid, "value": [-3.0, -9.0], "selected": true, "dims": [0], "follow": [1]})).unwrap();
+    assert_eq!(prop(&s, a, "audio/levels").value.components(), vec![-3.0, -9.0]);
+    assert_eq!(prop(&s, b, "audio/levels").value.components(), vec![-3.0, -13.0], "B rises 17 dB on both channels");
+    assert_eq!(s.history.undo.len(), undo + 1, "one undo step");
+
+    // Keyed at a time other than the CTI: B's change is measured on its key there.
+    animate(&mut s, b, "audio/levels", &[(0.0, json!([-20.0, -30.0])), (1.0, json!([-10.0, -40.0]))]);
+    s.execute("prop.set", json!({"layer": a, "prop": uid, "value": [-4.0, -10.0], "time": 1.0, "selected": true, "dims": [0], "follow": [1]})).unwrap();
+    let keys: Vec<Vec<f64>> = prop(&s, b, "audio/levels").keys.iter().map(|k| k.value.components()).collect();
+    assert_eq!(keys, vec![vec![-20.0, -30.0], vec![-4.0, -34.0]], "B's 1 s key rises 6 dB on both channels");
+}

crates/ui-egui/src/app/frame.rs

@@ -98,7 +98,7 @@ impl EffectcraftApp {
                     self.ui.timeline.pps = None;
                 }
                 effectcraft_engine::Event::Toast { message, .. } => self.toast = Some((message, self.now)),
-                effectcraft_engine::Event::OpenUrl(url) => open_url(ctx, url),
+                effectcraft_engine::Event::OpenUrl(url) => ctx.open_url(egui::OpenUrl::new_tab(url)),
                 // Frames are keyed by content: an edit keeps those of comps it doesn't touch.
                 effectcraft_engine::Event::ProjectChanged { .. } => {}
                 effectcraft_engine::Event::Frontend { command, params } => {
@@ -411,6 +411,8 @@ impl EffectcraftApp {
         header::show(self, ui, header);
         let body = egui::Rect::from_min_max(egui::pos2(full.min.x + 4.0, header.max.y + 2.0), egui::pos2(full.max.x - 4.0, full.max.y - 4.0));
         crate::color_picker::note_dialog(&ctx, self.dialog);
+        // After the shortcuts, menus and header, which can replace the project (New, Open).
+        self.ui.timeline.scope_links(self.session.script_ui.project_epoch);
         self.dock_area(ui, body);
         #[cfg(not(target_arch = "wasm32"))]
         prefs_live::dropped_files(self, ui, full);
@@ -581,48 +583,3 @@ impl EffectcraftApp {
         }
     }
 }
-
-/// Opens `url`: on Windows a `file://` folder (Reveal in Explorer) in File Explorer, since the
-/// system browser would get it otherwise (#1961); anything else in the browser.
-fn open_url(ctx: &egui::Context, url: String) {
-    #[cfg(windows)]
-    if let Some(path) = file_url_path(&url) {
-        // The engine only sends folders it checked are plain folders (`reveal_url`).
-        if std::process::Command::new("explorer").arg(&path).spawn().is_ok() {
-            return;
-        }
-    }
-    ctx.open_url(egui::OpenUrl::new_tab(url));
-}
-
-/// The Windows path of a `file:///C:/…` (or `file:////server/share/…`) URL, percent-decoded.
-#[cfg(any(windows, test))]
-fn file_url_path(url: &str) -> Option<String> {
-    let rest = url.strip_prefix("file:///")?;
-    let mut bytes = Vec::with_capacity(rest.len());
-    let mut it = rest.bytes();
-    while let Some(b) = it.next() {
-        if b == b'%' {
-            let hex = [it.next()?, it.next()?];
-            bytes.push(u8::from_str_radix(std::str::from_utf8(&hex).ok()?, 16).ok()?);
-        } else {
-            bytes.push(b);
-        }
-    }
-    let path = String::from_utf8(bytes).ok()?.replace('/', "\\");
-    // `file:////server/share` is the UNC path `\\server\share`.
-    Some(if path.starts_with('\\') { format!("\\{path}") } else { path })
-}
-
-#[cfg(test)]
-mod tests {
-    /// #1961: Reveal's `file://` URLs map back to the folder Explorer opens.
-    #[test]
-    fn file_urls_map_to_windows_paths() {
-        assert_eq!(super::file_url_path("file:///C:/Footage/My%20Shots/").as_deref(), Some("C:\\Footage\\My Shots\\"));
-        assert_eq!(super::file_url_path("file:///C:/Clips/%E6%98%A0%E5%83%8F").as_deref(), Some("C:\\Clips\\映像"));
-        assert_eq!(super::file_url_path("file:////server/share/x").as_deref(), Some("\\\\server\\share\\x"));
-        assert_eq!(super::file_url_path("https://getartcraft.com"), None);
-        assert_eq!(super::file_url_path("file:///C:/bad%2"), None);
-    }
-}

crates/ui-egui/src/panels/timeline.rs

@@ -5683,18 +5683,21 @@ fn vector_editor(app: &mut EffectcraftApp, ui: &mut egui::Ui, ve: &ValueEdit<'_>
     // Mask Feather: two linked values, never negative (as in After Effects, #203).
     let feather = prop.match_id == "feather" && layer.props.parent_of(uid).is_some_and(|g| matches!(g.kind, GroupKind::Mask { .. }));
     let range = if feather { (0.0, 1e9) } else { (-1e9, 1e9) };
+    // Audio Levels link their two channels too, off by default, by the same dB change (#2485).
+    let levels = prop.match_id == "levels" && layer.props.parent_of(uid).is_some_and(|g| g.match_id == "audio");
     // Scale and Mask Feather: the chain link (Constrain Proportions, on by default).
     // Rectangle and Ellipse Path Size have it too, off by default (#2489).
     let size = prop.match_id == "size" && layer.props.parent_of(uid).is_some_and(|g| matches!(g.match_id.as_str(), "rect" | "ellipse"));
-    let linkable = feather || size || (pct && prop.match_id == "scale");
-    let linked = linkable && app.ui.timeline.is_linked(uid, !size);
+    let linkable = feather || size || levels || (pct && prop.match_id == "scale");
+    let linked = linkable && app.ui.timeline.is_linked(uid, !(size || levels));
     if linkable {
         let lr = Rect::from_center_size(pos2(x + 7.0, at.y), vec2(14.0, 14.0));
-        let resp = ui.interact(lr, egui::Id::unique(("tl-link", uid)), Sense::click()).on_hover_text(crate::i18n::tr("Constrain Proportions"));
+        let label = if levels { "Link Channels" } else { "Constrain Proportions" };
+        let resp = ui.interact(lr, egui::Id::unique(("tl-link", uid)), Sense::click()).on_hover_text(crate::i18n::tr(label));
         icons::paint(p, lr, Icon::Link, if linked { t.accent } else { t.text_faint });
-        app.auto.add(&format!("timeline.prop.{uid}.link"), lr, "Constrain Proportions");
+        app.auto.add(&format!("timeline.prop.{uid}.link"), lr, label);
         if resp.clicked() {
-            app.ui.timeline.toggle_link(uid, !size);
+            app.ui.timeline.toggle_link(uid, !(size || levels));
         }
         x += 18.0;
     }
@@ -5715,7 +5718,8 @@ fn vector_editor(app: &mut EffectcraftApp, ui: &mut egui::Ui, ve: &ValueEdit<'_>
             // Alt edits one value of a linked pair (Ctrl+Alt is a proportional scrub).
             let shown = if linked && !ui.input(|i| i.modifiers.alt && !widgets::proportional_scrub(i.modifiers)) { n.min(c.len()) } else { 1 };
             let from = if shown == 1 { d } else { 0 };
-            for (e, v) in widgets::constrained(c.get(from..from + shown).unwrap_or_default(), d - from, nv).into_iter().enumerate() {
+            let link = if levels { widgets::shifted } else { widgets::constrained };
+            for (e, v) in link(c.get(from..from + shown).unwrap_or_default(), d - from, nv).into_iter().enumerate() {
                 if let Some(slot) = nc.get_mut(from + e) {
                     *slot = v;
                 }
@@ -5723,8 +5727,15 @@ fn vector_editor(app: &mut EffectcraftApp, ui: &mut egui::Ui, ve: &ValueEdit<'_>
             ve.set(actions, json!(nc));
             // Typed into these components only: other selected layers keep the rest of
             // their own value (#1434).
+            // Linked Audio Levels: the typed channel, the other following by that layer's own
+            // change, so each keeps its balance (#2485).
             if let Some((_, a)) = actions.last_mut() {
-                a["dims"] = json!((from..from + shown).collect::<Vec<_>>());
+                if levels {
+                    a["dims"] = json!([d]);
+                    a["follow"] = json!((from..from + shown).filter(|&e| e != d).collect::<Vec<_>>());
+                } else {
+                    a["dims"] = json!((from..from + shown).collect::<Vec<_>>());
+                }
             }
         }
         x = r.max.x + if d + 1 < n { 2.0 } else { 0.0 };

crates/ui-egui/src/state.rs

@@ -308,8 +308,8 @@ impl Default for ViewerState {
 
 impl TimelineState {
     /// Whether property `uid`'s chain link (Constrain Proportions) is on. One that starts linked
-    /// (Scale, Mask Feather) records a click in `unlinked`; one that starts unlinked (shape Size)
-    /// records it in `linked`.
+    /// (Scale, Mask Feather) records a click in `unlinked`; one that starts unlinked (shape Size,
+    /// Audio Levels) records it in `linked`.
     pub fn is_linked(&self, uid: u64, linked_by_default: bool) -> bool {
         if linked_by_default { !self.unlinked.contains(&uid) } else { self.linked.contains(&uid) }
     }
@@ -322,6 +322,16 @@ impl TimelineState {
         }
     }
 
+    /// Forget the chain links when the project was replaced (new or opened): they are keyed by
+    /// property uid, which the next project reuses, so a link turned on must not carry into it.
+    pub fn scope_links(&mut self, project_epoch: u64) {
+        if self.link_epoch != project_epoch {
+            self.link_epoch = project_epoch;
+            self.unlinked.clear();
+            self.linked.clear();
+        }
+    }
+
     /// Show `kinds` on `layers` (twirled open; empty: twirled closed) and remember it as the last
     /// reveal. Other layers keep theirs.
     pub fn apply_reveal(&mut self, layers: &[u64], kinds: Vec<String>) {
@@ -429,10 +439,13 @@ pub struct TimelineState {
     /// was turned off.
     #[serde(default)]
     pub unlinked: BTreeSet<u64>,
-    /// Shape Rectangle and Ellipse Path Size properties whose chain link (off by default) was
-    /// turned on (#2489).
+    /// Shape Rectangle and Ellipse Path Size (#2489) and Audio Levels (#2485) properties whose
+    /// chain link (off by default) was turned on.
     #[serde(default)]
     pub linked: BTreeSet<u64>,
+    /// The project (its epoch) `unlinked` and `linked` belong to.
+    #[serde(skip)]
+    pub link_epoch: u64,
     /// Visible optional columns (column header right-click ▸ Columns): `av`, `keys`, `label`,
     /// `num`, `comment`, `switches`, `parent`, `in`, `out`, `duration`, `stretch`. The name
     /// column is always shown; Modes follows `show_modes` (F4).
@@ -486,6 +499,7 @@ impl Default for TimelineState {
             expr_lines: BTreeMap::new(),
             unlinked: BTreeSet::new(),
             linked: BTreeSet::new(),
+            link_epoch: 0,
             columns: default_tl_columns(),
             source_name: false,
             scroll_to: None,

crates/ui-egui/src/widgets.rs

@@ -984,6 +984,13 @@ pub(crate) fn constrained(c: &[f64], d: usize, v: f64) -> Vec<f64> {
         .collect()
 }
 
+/// Linked values after component `d` of `c` became `v`: the others move by the same amount, so
+/// linked Audio Levels keep their stereo balance in dB (#2485).
+pub(crate) fn shifted(c: &[f64], d: usize, v: f64) -> Vec<f64> {
+    let Some(&old) = c.get(d) else { return c.to_vec() };
+    c.iter().enumerate().map(|(e, &x)| if e == d { v } else { x + (v - old) }).collect()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/ui-egui/tests/it/main.rs

@@ -76,6 +76,7 @@ mod ui_text_edit;
 mod ui_text_range_handles;
 mod ui_theme_favorites;
 mod ui_time_zoom_controls;
+mod ui_timeline_audio_levels;
 mod ui_timeline_effect_label;
 mod ui_timeline_pan;
 mod ui_timeline_shapes;

crates/ui-egui/tests/it/ui_timeline_audio_levels.rs

@@ -0,0 +1,166 @@
+//! Audio Levels' channel link in the Timeline (#2485): off by default; linked, an edit to one
+//! channel moves the other by the same dB, so the stereo balance stays, typed or scrubbed, on a
+//! static or animated property, and one Undo takes it back.
+
+use effectcraft_engine::Session;
+use effectcraft_engine::project::LayerId;
+use effectcraft_ui_egui::EffectcraftApp;
+use egui::{Event, Key, Modifiers, PointerButton, Pos2, pos2, vec2};
+use egui_kittest::Harness;
+use serde_json::json;
+
+fn center(h: &Harness<'_, EffectcraftApp>, id: &str) -> Pos2 {
+    let e = h.state().auto.find(id).unwrap_or_else(|| panic!("no {id}"));
+    pos2(e.rect[0] + e.rect[2] / 2.0, e.rect[1] + e.rect[3] / 2.0)
+}
+
+/// Press on `from`, move to `to` in `steps`, release there.
+fn drag(h: &mut Harness<'_, EffectcraftApp>, from: Pos2, to: Pos2, steps: u32) {
+    h.input_mut().events.push(Event::PointerMoved(from));
+    h.step();
+    h.input_mut().events.push(Event::PointerButton { pos: from, button: PointerButton::Primary, pressed: true, modifiers: Modifiers::NONE });
+    h.step();
+    for k in 1..=steps {
+        h.input_mut().events.push(Event::PointerMoved(from + (to - from) * (k as f32 / steps as f32)));
+        h.step();
+    }
+    h.input_mut().events.push(Event::PointerButton { pos: to, button: PointerButton::Primary, pressed: false, modifiers: Modifiers::NONE });
+    h.run_steps(3);
+}
+
+fn click(h: &mut Harness<'_, EffectcraftApp>, id: &str) {
+    let p = center(h, id);
+    drag(h, p, p, 1);
+}
+
+fn type_value(h: &mut Harness<'_, EffectcraftApp>, id: &str, v: &str) {
+    click(h, id);
+    h.input_mut().events.push(Event::Text(v.into()));
+    h.step();
+    h.input_mut().events.push(Event::Key { key: Key::Enter, physical_key: None, pressed: true, repeat: false, modifiers: Modifiers::NONE });
+    h.run_steps(3);
+}
+
+/// A precomp layer (which has Audio Levels) in comp Main at `levels`; its layer id and the
+/// property's uid.
+fn add_sound_layer(s: &mut Session, levels: [f64; 2]) -> (u64, u64) {
+    let l = s.execute("layer.addItem", json!({"item": "Sound"})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("prop.set", json!({"layer": l, "path": "audio/levels", "value": levels})).unwrap();
+    (l, s.active_comp().unwrap().layer(LayerId(l)).unwrap().props.prop("audio/levels").unwrap().uid)
+}
+
+/// Comps Sound and Main.
+fn comps(s: &mut Session) {
+    s.execute("comp.new", json!({"name": "Sound", "width": 64, "height": 36, "duration": 4})).unwrap();
+    s.execute("comp.new", json!({"name": "Main", "width": 320, "height": 180, "duration": 4})).unwrap();
+}
+
+/// Twirl layer `l` open to its property `uid`.
+fn reveal(h: &mut Harness<'_, EffectcraftApp>, l: u64, uid: u64) {
+    h.state_mut().ui.timeline.open_layers.insert(l);
+    h.state_mut().ui.timeline.layer_reveal.insert(l, vec!["props".into()]);
+    h.state_mut().ui.timeline.reveal_props.insert(uid);
+    h.run_steps(3);
+}
+
+fn levels_of(h: &Harness<'_, EffectcraftApp>, l: u64) -> Vec<f64> {
+    h.state().session.active_comp().unwrap().layer(LayerId(l)).unwrap().props.prop("audio/levels").unwrap().value.components()
+}
+
+#[test]
+fn linked_audio_levels_move_both_channels_by_the_same_db() {
+    let mut s = Session::default();
+    comps(&mut s);
+    let (l, uid) = add_sound_layer(&mut s, [-6.0, -12.0]);
+    let mut h = Harness::builder().with_size(vec2(1600.0, 1000.0)).build_eframe(|_| EffectcraftApp::new(s));
+    reveal(&mut h, l, uid);
+    let levels =
+        |h: &Harness<'_, EffectcraftApp>| h.state().session.active_comp().unwrap().layer(LayerId(l)).unwrap().props.prop("audio/levels").unwrap().clone();
+    let set = |h: &mut Harness<'_, EffectcraftApp>, v: [f64; 2]| {
+        h.state_mut().session.execute("prop.set", json!({"layer": l, "path": "audio/levels", "value": v})).unwrap();
+        h.run_steps(2);
+    };
+    let undo = |h: &mut Harness<'_, EffectcraftApp>| {
+        h.state_mut().session.execute("edit.undo", json!({})).unwrap();
+        h.run_steps(2);
+    };
+    let (left, right, link) = (format!("timeline.prop.{uid}.value.0"), format!("timeline.prop.{uid}.value.1"), format!("timeline.prop.{uid}.link"));
+    assert_eq!(h.state().auto.find(&link).unwrap().label, "Link Channels");
+
+    type_value(&mut h, &left, "-3");
+    assert_eq!(levels(&h).value.components(), vec![-3.0, -12.0], "unlinked by default, one channel moves alone");
+    set(&mut h, [-6.0, -12.0]);
+
+    click(&mut h, &link);
+    type_value(&mut h, &left, "-3");
+    assert_eq!(levels(&h).value.components(), vec![-3.0, -9.0], "linked, both rise 3 dB and keep their 6 dB balance");
+    undo(&mut h);
+    assert_eq!(levels(&h).value.components(), vec![-6.0, -12.0], "one Undo takes back both channels");
+
+    type_value(&mut h, &right, "0");
+    assert_eq!(levels(&h).value.components(), vec![6.0, 0.0], "the right channel leads just the same");
+    set(&mut h, [0.0, 0.0]);
+    type_value(&mut h, &left, "-6");
+    assert_eq!(levels(&h).value.components(), vec![-6.0, -6.0], "equal channels at 0 dB stay equal");
+
+    set(&mut h, [-6.0, -12.0]);
+    let from = center(&h, &left);
+    drag(&mut h, from, from + vec2(30.0, 0.0), 6);
+    let c = levels(&h).value.components();
+    assert!(c[0] > -6.0, "the scrub raised the left channel: {c:?}");
+    assert!((c[0] - c[1] - 6.0).abs() < 1e-9, "a linked scrub keeps the balance: {c:?}");
+    undo(&mut h);
+    assert_eq!(levels(&h).value.components(), vec![-6.0, -12.0], "one Undo takes back the whole scrub");
+
+    // Animated: the edit at the current time changes that key's two channels together.
+    h.state_mut().session.execute("prop.addKey", json!({"layer": l, "path": "audio/levels", "time": 0.0, "value": [-6.0, -12.0]})).unwrap();
+    h.state_mut().session.execute("prop.addKey", json!({"layer": l, "path": "audio/levels", "time": 1.0, "value": [0.0, 0.0]})).unwrap();
+    h.run_steps(2);
+    type_value(&mut h, &left, "-10");
+    let keys: Vec<Vec<f64>> = levels(&h).keys.iter().map(|k| k.value.components()).collect();
+    assert_eq!(keys, vec![vec![-10.0, -16.0], vec![0.0, 0.0]], "the key at the current time moves both channels");
+
+    click(&mut h, &link);
+    type_value(&mut h, &left, "-4");
+    let keys: Vec<Vec<f64>> = levels(&h).keys.iter().map(|k| k.value.components()).collect();
+    assert_eq!(keys[0], vec![-4.0, -16.0], "unlinked again, the right channel stays");
+}
+
+/// With several layers selected, a linked typed Left sets each layer's Left and moves its Right
+/// by that layer's own change: every layer keeps its own balance.
+#[test]
+fn linked_typing_keeps_each_selected_layers_own_balance() {
+    let mut s = Session::default();
+    comps(&mut s);
+    let (a, uid) = add_sound_layer(&mut s, [-6.0, -12.0]);
+    let (b, other) = add_sound_layer(&mut s, [-20.0, -30.0]);
+    s.execute("layer.select", json!({"layers": [a, b]})).unwrap();
+    let mut h = Harness::builder().with_size(vec2(1600.0, 1000.0)).build_eframe(|_| EffectcraftApp::new(s));
+    reveal(&mut h, a, uid);
+    reveal(&mut h, b, other);
+    click(&mut h, &format!("timeline.prop.{uid}.link"));
+    type_value(&mut h, &format!("timeline.prop.{uid}.value.0"), "-3");
+    assert_eq!(levels_of(&h, a), vec![-3.0, -9.0]);
+    assert_eq!(levels_of(&h, b), vec![-3.0, -13.0], "B rises 17 dB on both channels, keeping its 10 dB balance");
+}
+
+/// A link turned on does not carry into a new project whose Audio Levels reuse the property uid.
+#[test]
+fn a_new_project_starts_with_its_audio_levels_unlinked() {
+    let mut s = Session::default();
+    comps(&mut s);
+    let (l, uid) = add_sound_layer(&mut s, [0.0, 0.0]);
+    let mut h = Harness::builder().with_size(vec2(1600.0, 1000.0)).build_eframe(|_| EffectcraftApp::new(s));
+    reveal(&mut h, l, uid);
+    click(&mut h, &format!("timeline.prop.{uid}.link"));
+    assert!(h.state().ui.timeline.is_linked(uid, false));
+
+    h.state_mut().session.execute("file.newProject", json!({})).unwrap();
+    comps(&mut h.state_mut().session);
+    let (l, again) = add_sound_layer(&mut h.state_mut().session, [0.0, 0.0]);
+    assert_eq!(again, uid, "the new project reuses the property uid");
+    reveal(&mut h, l, again);
+    assert!(!h.state().ui.timeline.is_linked(again, false), "the new project's levels start unlinked");
+    type_value(&mut h, &format!("timeline.prop.{again}.value.0"), "-3");
+    assert_eq!(levels_of(&h, l), vec![-3.0, 0.0]);
+}