Roll: reversed clips take the cut from the opposite source end (#526)

crates/edit/src/lib.rs

@@ -751,10 +751,19 @@ pub fn roll(seq: &mut Sequence, left: ClipId, right: ClipId, delta: Tick, ctx: &
     let mut d = delta;
     // left out-point limits
     d = d.max(-(l.duration - ctx.min_duration)).min(r.duration - ctx.min_duration);
-    if let Some(m) = media_len(ctx, l) {
+    // a reversed clip consumes media from the opposite end, so its media limit is the other one
+    if l.reverse {
+        d = d.min(Tick((head(ctx, l).0 as f64 / l.speed.abs()).floor() as i64));
+    } else if let Some(m) = media_len(ctx, l) {
         d = d.min(Tick(((m - l.source_out()).0 as f64 / l.speed.abs()).floor() as i64));
     }
-    d = d.max(-Tick((head(ctx, r).0 as f64 / r.speed.abs()).floor() as i64));
+    if r.reverse {
+        if let Some(m) = media_len(ctx, r) {
+            d = d.max(-Tick(((m - r.source_out()).0 as f64 / r.speed.abs()).floor() as i64));
+        }
+    } else {
+        d = d.max(-Tick((head(ctx, r).0 as f64 / r.speed.abs()).floor() as i64));
+    }
     if d == Tick::ZERO {
         return Ok(d);
     }
@@ -762,15 +771,19 @@ pub fn roll(seq: &mut Sequence, left: ClipId, right: ClipId, delta: Tick, ctx: &
     let before = seq.clone();
     {
         let (_, l) = seq.find_item_mut(left).ok_or(EditError::NoItem(left))?;
+        if l.reverse {
+            l.source_in -= src_of(d, ls);
+        }
         l.duration += d;
     }
     {
         let (_, r) = seq.find_item_mut(right).ok_or(EditError::NoItem(right))?;
         r.start += d;
         r.duration -= d;
-        r.source_in += src_of(d, rs);
+        if !r.reverse {
+            r.source_in += src_of(d, rs);
+        }
     }
-    let _ = ls;
     transitions_follow_cuts(&before, seq);
     Ok(d)
 }

crates/edit/src/tests.rs

@@ -673,3 +673,21 @@ fn shorter_head_closes_the_stretch_after_the_cut_on_sync_locked_tracks() {
         assert_eq!(fx.spans(v1), vec![(0, 10), (10, 10), (20, 10)], "unchanged on failure");
     }
 }
+
+#[test]
+fn roll_reversed_clips_keeps_media_mapping() {
+    let mut fx = Fx::new();
+    let v = fx.v(0);
+    let mut a = fx.item(0, 30, 20);
+    a.reverse = true;
+    let mut b = fx.item(30, 30, 50);
+    b.reverse = true;
+    let (ia, ib) = (a.id, b.id);
+    fx.seq.track_mut(v).unwrap().items.extend([a, b]);
+    let mut n = 0;
+    roll(&mut fx.seq, ia, ib, f(10), &mut Fx::ctx(&mut n)).unwrap();
+    let (_, l) = fx.seq.find_item(ia).unwrap();
+    assert_eq!((l.start, l.duration, l.source_in), (f(0), f(40), f(10)));
+    let (_, r) = fx.seq.find_item(ib).unwrap();
+    assert_eq!((r.start, r.duration, r.source_in), (f(40), f(20), f(50)));
+}