Fallback layout animations by motion group

docs/window-animations-plan.md

@@ -221,6 +221,9 @@ Current pure planner status:
   orientations: peer/container space scales first, the extracted child moves
   only after space exists, and orthogonal growth happens in the final phase.
 - Every produced plan is sampled for overlap at each phase before it is accepted.
+- Live layout batches are partitioned by overlapping motion bounds, so unrelated
+  groups can still use multiphase animation when another group falls back to
+  linear motion.
 
 Tests:
 

src/animation/multiphase.rs

@@ -81,6 +81,33 @@ pub fn plan_no_overlap(request: &MultiphaseRequest) -> Result<MultiphasePlan, Mu
     Err(MultiphaseError::NoPlan)
 }
 
+pub(crate) fn partition_motion_groups(windows: &[MultiphaseWindow]) -> Vec<Vec<usize>> {
+    let mut groups = vec![];
+    let mut seen = vec![false; windows.len()];
+    for start in 0..windows.len() {
+        if seen[start] {
+            continue;
+        }
+        seen[start] = true;
+        let mut group = vec![];
+        let mut pending = vec![start];
+        while let Some(idx) = pending.pop() {
+            group.push(idx);
+            let bounds = motion_bounds(windows[idx]);
+            for other in 0..windows.len() {
+                if seen[other] || !bounds.intersects(&motion_bounds(windows[other])) {
+                    continue;
+                }
+                seen[other] = true;
+                pending.push(other);
+            }
+        }
+        group.sort_unstable();
+        groups.push(group);
+    }
+    groups
+}
+
 fn validate_request(request: &MultiphaseRequest) -> Result<(), MultiphaseError> {
     if request.bounds.is_empty() {
         return Err(MultiphaseError::EmptyBounds);
@@ -380,6 +407,10 @@ fn overlaps(rects: impl IntoIterator<Item = Rect>) -> bool {
     false
 }
 
+fn motion_bounds(window: MultiphaseWindow) -> Rect {
+    window.from.union(window.to)
+}
+
 fn push_step(steps: &mut Vec<MultiphaseStep>, node_id: NodeId, from: Rect, to: Rect) {
     if from != to {
         steps.push(MultiphaseStep { node_id, from, to });
@@ -697,4 +728,48 @@ mod tests {
         }]);
         assert_eq!(plan_no_overlap(&req), Err(MultiphaseError::NoPlan));
     }
+
+    #[test]
+    fn motion_groups_split_disjoint_layout_changes() {
+        let windows = vec![
+            MultiphaseWindow {
+                node_id: id(1),
+                from: rect(0, 0, 100, 100),
+                to: rect(100, 0, 200, 100),
+            },
+            MultiphaseWindow {
+                node_id: id(2),
+                from: rect(100, 0, 200, 100),
+                to: rect(0, 0, 100, 100),
+            },
+            MultiphaseWindow {
+                node_id: id(3),
+                from: rect(300, 0, 400, 100),
+                to: rect(400, 0, 500, 100),
+            },
+        ];
+        assert_eq!(partition_motion_groups(&windows), vec![vec![0, 1], vec![2]]);
+    }
+
+    #[test]
+    fn motion_groups_are_transitive() {
+        let windows = vec![
+            MultiphaseWindow {
+                node_id: id(1),
+                from: rect(0, 0, 100, 100),
+                to: rect(80, 0, 180, 100),
+            },
+            MultiphaseWindow {
+                node_id: id(2),
+                from: rect(170, 0, 270, 100),
+                to: rect(250, 0, 350, 100),
+            },
+            MultiphaseWindow {
+                node_id: id(3),
+                from: rect(90, 0, 180, 100),
+                to: rect(180, 0, 260, 100),
+            },
+        ];
+        assert_eq!(partition_motion_groups(&windows), vec![vec![0, 1, 2]]);
+    }
 }

src/state.rs

@@ -5,7 +5,9 @@ use {
         animation::{
             AnimationCurve, AnimationState, AnimationTick, RetainedExitLayer, RetainedToplevel,
             expand_damage_rect,
-            multiphase::{MultiphaseRequest, MultiphaseWindow, plan_no_overlap},
+            multiphase::{
+                MultiphaseRequest, MultiphaseWindow, partition_motion_groups, plan_no_overlap,
+            },
             spawn_in_start_rect,
         },
         async_engine::{AsyncEngine, SpawnedFuture},
@@ -1586,51 +1588,59 @@ impl State {
             return;
         };
         let now = self.now_nsec();
-        if self.start_multiphase_layout_animation(&candidates, now) {
-            return;
-        }
-        for candidate in candidates {
-            self.start_layout_animation_candidate(candidate, now);
-        }
-    }
-
-    fn start_multiphase_layout_animation(
-        self: &Rc<Self>,
-        candidates: &[LayoutAnimationCandidate],
-        now_nsec: u64,
-    ) -> bool {
-        if candidates.len() < 2 {
-            return false;
-        }
         let windows: Vec<_> = candidates
             .iter()
             .map(|candidate| MultiphaseWindow {
                 node_id: candidate.node_id,
                 from: self
                     .animations
-                    .visual_rect(candidate.node_id, candidate.old, now_nsec),
+                    .visual_rect(candidate.node_id, candidate.old, now),
                 to: candidate.new,
             })
             .collect();
-        let Some(first) = windows.first() else {
+        for group in partition_motion_groups(&windows) {
+            if self.start_multiphase_layout_animation(&candidates, &windows, &group, now) {
+                continue;
+            }
+            for idx in group {
+                self.start_layout_animation_candidate(candidates[idx].clone(), now);
+            }
+        }
+    }
+
+    fn start_multiphase_layout_animation(
+        self: &Rc<Self>,
+        candidates: &[LayoutAnimationCandidate],
+        windows: &[MultiphaseWindow],
+        group: &[usize],
+        now_nsec: u64,
+    ) -> bool {
+        if group.len() < 2 {
+            return false;
+        }
+        let request_windows: Vec<_> = group.iter().map(|&idx| windows[idx]).collect();
+        let Some(first) = request_windows.first() else {
             return false;
         };
         let mut bounds = first.from.union(first.to);
-        for window in &windows[1..] {
+        for window in &request_windows[1..] {
             bounds = bounds.union(window.from).union(window.to);
         }
-        let Ok(plan) = plan_no_overlap(&MultiphaseRequest { bounds, windows }) else {
+        let Ok(plan) = plan_no_overlap(&MultiphaseRequest {
+            bounds,
+            windows: request_windows,
+        }) else {
             return false;
         };
         if plan.phases.is_empty() {
             return false;
         }
         let mut entries = vec![];
-        for candidate in candidates {
-            let mut current =
-                self.animations
-                    .visual_rect(candidate.node_id, candidate.old, now_nsec);
-            let mut damage = current.union(candidate.new);
+        for &idx in group {
+            let candidate = &candidates[idx];
+            let window = windows[idx];
+            let mut current = window.from;
+            let mut damage = current.union(window.to);
             let mut phases = vec![];
             for phase in &plan.phases {
                 match phase
@@ -1646,7 +1656,7 @@ impl State {
                     None => phases.push((current, current)),
                 }
             }
-            if current != candidate.new {
+            if current != window.to {
                 return false;
             }
             let retained = self