Keyboard slip: clamp linked clips by one shared delta (#529)

crates/engine/src/clip_ops_tests.rs

@@ -923,3 +923,30 @@ fn linked_slip_keeps_picture_and_sound_aligned_at_unequal_media_limits() {
     s.execute("timeline.slip", json!({"clip": v, "deltaFrames": -10})).unwrap();
     assert_eq!((clip(&s, v).source_in, clip(&s, a).source_in), (Tick(fr.0 * 10), Tick(fr.0 * 10)));
 }
+
+#[test]
+fn keyboard_slip_keeps_linked_clips_in_sync_past_the_shorter_handle() {
+    let mut s = Session::default();
+    s.execute("file.newProject", json!({"name": "Slip"})).unwrap();
+    s.execute("file.newSequence", json!({"name": "Sequence", "fps": 25, "video": 1, "audio": 1, "width": 16, "height": 16})).unwrap();
+    let r = s.execute("file.newOfflineFile", json!({"name": "Media", "seconds": 4, "fps": 25, "video": true, "audio": true})).unwrap();
+    let item = r["item"].as_u64().unwrap();
+    let fr = s.sequence_rate().tick_of(1);
+    let r =
+        s.execute("timeline.place", json!({"item": item, "track": "V1", "audioTrack": "A1", "time": 0, "sourceIn": fr.0 * 20, "duration": fr.0 * 60})).unwrap();
+    let (v, a) = (r["clips"][0].as_u64().unwrap(), r["clips"][1].as_u64().unwrap());
+    // lengthen only the picture: it keeps 10 frames of tail handle, the sound keeps 20
+    s.execute("sequence.linkedSelection", json!({"on": false})).unwrap();
+    s.execute("timeline.trim", json!({"clip": v, "edge": "out", "deltaFrames": 10})).unwrap();
+    s.execute("sequence.linkedSelection", json!({"on": true})).unwrap();
+    s.execute("timeline.select", json!({"clips": [v, a]})).unwrap();
+    for _ in 0..3 {
+        s.execute("timeline.slipLeft5", json!({})).unwrap();
+    }
+    assert_eq!((clip(&s, v).source_in, clip(&s, a).source_in), (Tick(fr.0 * 30), Tick(fr.0 * 30)));
+    // with linked selection off each selected clip still slips on its own
+    s.execute("sequence.linkedSelection", json!({"on": false})).unwrap();
+    s.execute("timeline.select", json!({"clips": [v, a]})).unwrap();
+    s.execute("timeline.slipLeft5", json!({})).unwrap();
+    assert_eq!((clip(&s, v).source_in, clip(&s, a).source_in), (Tick(fr.0 * 30), Tick(fr.0 * 35)));
+}

crates/engine/src/commands.rs

@@ -340,6 +340,24 @@ fn move_clips(s: &mut Session, p: &Value) -> Result<Value> {
     Ok(json!({"moved": moves.iter().map(|m| m.0.0).collect::<Vec<_>>(), "overwritten": overwritten}))
 }
 
+/// Slip clips together: the media delta of each clip is scaled down by the same factor so that the
+/// most constrained clip (media end or start) still moves, and no linked partner slips further.
+pub(crate) fn slip_together(q: &mut filmcraft_project::Sequence, ctx: &mut edit::EditCtx<'_>, deltas: &[(ClipId, Tick)]) -> Result<()> {
+    let mut scale = 1.0_f64;
+    for (c, d) in deltas {
+        if d.0 == 0 {
+            continue;
+        }
+        let x = edit::slip(&mut q.clone(), *c, *d, ctx)?;
+        scale = scale.min(x.0.abs() as f64 / d.0.abs() as f64);
+    }
+    for (c, d) in deltas {
+        let dd = if scale < 1.0 { Tick((d.0 as f64 * scale).round() as i64) } else { *d };
+        edit::slip(q, *c, dd, ctx)?;
+    }
+    Ok(())
+}
+
 /// Expand a clip selection with linked partners (when linked selection is on).
 pub fn with_links(s: &Session, clips: &[ClipId]) -> Vec<ClipId> {
     let Some(seq) = s.active_sequence() else { return clips.to_vec() };
@@ -2220,17 +2238,8 @@ fn build() -> Vec<CommandSpec> {
             let clips = with_links(s, &[c]);
             s.edit_sequence("Slip", |q, ctx, _| {
                 // clamp across all linked partners, then slip them by the common delta
-                let mut dd = d;
-                for c in &clips {
-                    let x = edit::slip(&mut q.clone(), *c, dd, ctx)?;
-                    if x.abs() < dd.abs() {
-                        dd = x;
-                    }
-                }
-                for c in &clips {
-                    edit::slip(q, *c, dd, ctx)?;
-                }
-                Ok(())
+                let deltas: Vec<(ClipId, Tick)> = clips.iter().map(|c| (*c, d)).collect();
+                slip_together(q, ctx, &deltas)
             })?;
             Ok(Value::Null)
         }),

crates/engine/src/keyboard.rs

@@ -40,7 +40,7 @@ use filmcraft_project::{ClipId, ItemKind, ParamValue, Sequence, TrackId, TrackKi
 use filmcraft_time::Tick;
 use serde_json::{Value, json};
 
-use crate::commands::{CommandSpec, always, bad, has_selection, has_seq, item_p, time_p, with_links};
+use crate::commands::{CommandSpec, always, bad, has_selection, has_seq, item_p, slip_together, time_p, with_links};
 use crate::{EngineError, Result, Session};
 
 type Run = fn(&mut Session, &Value) -> Result<Value>;
@@ -248,14 +248,21 @@ fn slip_selection(s: &mut Session, frames: i64) -> Result<Value> {
     let rate = s.sequence_rate();
     let clips = with_links(s, &s.state.selection.clone());
     let seq = s.active_sequence().ok_or(EngineError::NoSequence)?;
-    // media delta per clip (source frames run at the clip's speed)
-    let deltas: Vec<(ClipId, Tick)> = clips
-        .iter()
-        .filter_map(|c| seq.find_item(*c).map(|(_, i)| (*c, Tick((rate.tick_of(frames).0 as f64 * i.speed.abs().max(1e-9)).round() as i64))))
-        .collect();
+    let linked = s.state.linked_selection;
+    // media delta per clip (source frames run at the clip's speed); linked partners slip as one group
+    let mut groups: Vec<(Option<u64>, Vec<(ClipId, Tick)>)> = Vec::new();
+    for c in &clips {
+        let Some((_, i)) = seq.find_item(*c) else { continue };
+        let d = Tick((rate.tick_of(frames).0 as f64 * i.speed.abs().max(1e-9)).round() as i64);
+        let link = i.link.filter(|_| linked);
+        match groups.iter_mut().find(|(l, _)| link.is_some() && *l == link) {
+            Some((_, g)) => g.push((*c, d)),
+            None => groups.push((link, vec![(*c, d)])),
+        }
+    }
     s.edit_sequence("Slip", |q, ctx, _| {
-        for (c, d) in &deltas {
-            edit::slip(q, *c, *d, ctx)?;
+        for (_, g) in &groups {
+            slip_together(q, ctx, g)?;
         }
         Ok(())
     })?;