Handle phased animation retargeting

docs/window-animations-testing.md

@@ -288,8 +288,27 @@ Hard failure:
 
 ## 9. Mixed-Action Phases
 
-Look for layouts where one window can move on one axis while another window
+This case is easiest to prove with the planner tests because Wry currently has
-scales on a different axis in the same proven phase.
+few user commands that create a same-batch move for one tiled window and an
+independent resize for another. The canonical geometry is:
+
+```text
+start:  A = (0,0)-(80,80)      B = (200,0)-(280,80)
+target: A = (40,0)-(120,80)    B = (200,0)-(280,120)
+```
+
+`A` moves horizontally while `B` scales vertically. The windows are far enough
+apart that the mixed phase is provably non-overlapping.
+
+To exercise the current proof directly, run:
+
+```sh
+cargo test animation::multiphase::tests::mixed_single_phase_accepts_move_and_scale_when_proven
+```
+
+For visual/manual testing, use any command sequence that can produce the same
+shape in one layout batch: one window changes only x-position, and a separate,
+non-overlapping window changes only height.
 
 Expected:
 
@@ -298,8 +317,8 @@ Expected:
 - no individual window moves diagonally
 - no overlap occurs at any point during the phase
 
-This is easier to confirm with debug fallback logs plus visual inspection. A
+A fallback here is acceptable if no normal user command can create this geometry;
-fallback here is acceptable if the planner cannot prove the sequence.
+the planner test above is the authority for the mixed-action rule.
 
 ## 10. Mono Mode
 

src/animation.rs

@@ -474,6 +474,20 @@ impl AnimationState {
         }
     }
 
+    pub fn phased_route_to(
+        &self,
+        node_id: NodeId,
+        target: Rect,
+        now_nsec: u64,
+    ) -> Option<Vec<(Rect, Rect)>> {
+        let phased = self.phased.borrow();
+        let anim = phased.get(&node_id)?;
+        if anim.done(now_nsec) {
+            return None;
+        }
+        anim.route_to(target, now_nsec)
+    }
+
     pub fn exit_frames(&self, now_nsec: u64) -> Vec<RetainedExitFrame> {
         self.exits
             .borrow()
@@ -614,6 +628,52 @@ impl PhasedWindowAnimation {
         let t = self.curve.sample(t);
         lerp_rect(segment.from, segment.to, t)
     }
+
+    fn phase_at(&self, now_nsec: u64) -> Option<usize> {
+        if self.duration_nsec == 0 || self.segments.is_empty() {
+            return None;
+        }
+        let elapsed = now_nsec.saturating_sub(self.start_nsec);
+        let phase = (elapsed / self.duration_nsec) as usize;
+        (phase < self.segments.len()).then_some(phase)
+    }
+
+    fn path_points(&self) -> Option<Vec<Rect>> {
+        let first = self.segments.first()?;
+        let mut points = vec![first.from];
+        points.extend(self.segments.iter().map(|segment| segment.to));
+        Some(points)
+    }
+
+    fn route_to(&self, target: Rect, now_nsec: u64) -> Option<Vec<(Rect, Rect)>> {
+        let phase = self.phase_at(now_nsec)?;
+        let points = self.path_points()?;
+        let target_idx = points.iter().position(|point| *point == target)?;
+        let current = self.rect_at(now_nsec);
+        if current == target {
+            return Some(vec![]);
+        }
+
+        let mut route = vec![];
+        if target_idx <= phase {
+            push_non_empty_segment(&mut route, current, points[phase]);
+            for idx in (target_idx..phase).rev() {
+                push_non_empty_segment(&mut route, points[idx + 1], points[idx]);
+            }
+        } else {
+            push_non_empty_segment(&mut route, current, points[phase + 1]);
+            for idx in (phase + 1)..target_idx {
+                push_non_empty_segment(&mut route, points[idx], points[idx + 1]);
+            }
+        }
+        Some(route)
+    }
+}
+
+fn push_non_empty_segment(route: &mut Vec<(Rect, Rect)>, from: Rect, to: Rect) {
+    if from != to {
+        route.push((from, to));
+    }
 }
 
 struct ExitAnimation {
@@ -863,6 +923,52 @@ mod tests {
         assert_eq!(state.visual_rect(id, c, 200_000_000), c);
     }
 
+    #[test]
+    fn phased_route_reverses_to_existing_endpoint() {
+        let state = AnimationState::default();
+        let id = NodeId(1);
+        let a = Rect::new_sized_saturating(0, 0, 100, 100);
+        let b = Rect::new_sized_saturating(0, 0, 100, 50);
+        let c = Rect::new_sized_saturating(100, 0, 100, 50);
+        assert!(state.set_phased_target(
+            id,
+            vec![(a, b), (b, c)],
+            None,
+            0,
+            100,
+            AnimationCurve::Linear
+        ));
+
+        let current = lerp_rect(b, c, 0.5);
+        assert_eq!(
+            state.phased_route_to(id, a, 150_000_000).unwrap(),
+            vec![(current, b), (b, a)]
+        );
+    }
+
+    #[test]
+    fn phased_route_continues_to_existing_endpoint() {
+        let state = AnimationState::default();
+        let id = NodeId(1);
+        let a = Rect::new_sized_saturating(0, 0, 100, 100);
+        let b = Rect::new_sized_saturating(0, 0, 100, 50);
+        let c = Rect::new_sized_saturating(100, 0, 100, 50);
+        assert!(state.set_phased_target(
+            id,
+            vec![(a, b), (b, c)],
+            None,
+            0,
+            100,
+            AnimationCurve::Linear
+        ));
+
+        let current = lerp_rect(a, b, 0.5);
+        assert_eq!(
+            state.phased_route_to(id, c, 50_000_000).unwrap(),
+            vec![(current, b), (b, c)]
+        );
+    }
+
     #[test]
     fn linear_retarget_interrupts_phased_animation_from_current_rect() {
         let state = AnimationState::default();

src/animation/multiphase.rs

@@ -402,6 +402,52 @@ pub fn plan_no_overlap_explained(
     }
 }
 
+pub(crate) fn validate_phase_paths(
+    request: &MultiphaseRequest,
+    paths: &[Vec<(Rect, Rect)>],
+) -> Result<MultiphasePlan, MultiphasePlanFailure> {
+    if paths.len() != request.windows.len() {
+        return Err(MultiphasePlanFailure::NoPattern);
+    }
+    let phase_count = paths.iter().map(Vec::len).max().unwrap_or(0);
+    if phase_count == 0 {
+        return Err(MultiphasePlanFailure::NoPattern);
+    }
+    let mut phases = vec![];
+    for phase_idx in 0..phase_count {
+        let mut steps = vec![];
+        let mut actions = vec![];
+        for (window_idx, path) in paths.iter().enumerate() {
+            let Some((from, to)) = path.get(phase_idx).copied() else {
+                continue;
+            };
+            if from == to {
+                continue;
+            }
+            let step = MultiphaseStep {
+                node_id: request.windows[window_idx].node_id,
+                from,
+                to,
+            };
+            let Some(action) = classify_step(step) else {
+                return Err(MultiphasePlanFailure::NoPattern);
+            };
+            steps.push(step);
+            actions.push(action);
+        }
+        if !steps.is_empty() {
+            phases.push(MultiphasePhase {
+                action: MultiphasePhaseAction::from_step_actions(actions),
+                steps,
+            });
+        }
+    }
+    let plan = MultiphasePlan { phases };
+    validate_plan_continuous_diagnostic(request, &plan)
+        .map(|_| plan)
+        .map_err(MultiphasePlanFailure::Validation)
+}
+
 pub(crate) fn partition_motion_groups(windows: &[MultiphaseWindow]) -> Vec<Vec<usize>> {
     let mut groups = vec![];
     let mut seen = vec![false; windows.len()];
@@ -2378,6 +2424,42 @@ mod tests {
         assert!(validate_plan_continuous(&req, plan));
     }
 
+    #[test]
+    fn validated_phase_paths_accept_interrupted_reverse_route() {
+        let a_current = rect(50, 0, 150, 50);
+        let b_current = rect(50, 50, 150, 100);
+        let req = request(vec![
+            window(1, a_current, rect(0, 0, 100, 100)),
+            window(2, b_current, rect(100, 0, 200, 100)),
+        ]);
+        let paths = vec![
+            vec![
+                (a_current, rect(0, 0, 100, 50)),
+                (rect(0, 0, 100, 50), rect(0, 0, 100, 100)),
+            ],
+            vec![
+                (b_current, rect(100, 50, 200, 100)),
+                (rect(100, 50, 200, 100), rect(100, 0, 200, 100)),
+            ],
+        ];
+
+        let plan = validate_phase_paths(&req, &paths).unwrap();
+        assert_eq!(
+            actions(&plan),
+            vec![
+                PhaseAction {
+                    kind: PhaseKind::Move,
+                    axis: PhaseAxis::Horizontal,
+                },
+                PhaseAction {
+                    kind: PhaseKind::Scale,
+                    axis: PhaseAxis::Vertical,
+                },
+            ]
+        );
+        assert!(validate_plan_continuous(&req, &plan));
+    }
+
     #[test]
     fn bounded_generated_supported_split_tree_corpus_is_deterministic() {
         let mut cases = vec![];

src/state.rs

@@ -7,7 +7,7 @@ use {
             expand_damage_rect,
             multiphase::{
                 MultiphaseRequest, MultiphaseWindow, MultiphaseWindowHierarchy,
-                partition_motion_groups, plan_no_overlap_with_diagnostics,
+                partition_motion_groups, plan_no_overlap_with_diagnostics, validate_phase_paths,
             },
             spawn_in_start_rect,
         },
@@ -1679,6 +1679,9 @@ impl State {
             windows: request_windows,
             clearance: self.layout_animation_clearance(),
         };
+        if self.start_existing_phased_retarget(candidates, windows, group, &request, now_nsec) {
+            return true;
+        }
         let plan = match plan_no_overlap_with_diagnostics(&request) {
             Ok(plan) => plan,
             Err(diagnostic) => {
@@ -1690,7 +1693,53 @@ impl State {
                 return false;
             }
         };
-        if plan.phases.is_empty() {
+        self.start_multiphase_plan(candidates, windows, group, &plan.phases, now_nsec)
+    }
+
+    fn start_existing_phased_retarget(
+        self: &Rc<Self>,
+        candidates: &[LayoutAnimationCandidate],
+        windows: &[MultiphaseWindow],
+        group: &[usize],
+        request: &MultiphaseRequest,
+        now_nsec: u64,
+    ) -> bool {
+        let mut paths = vec![];
+        for &idx in group {
+            let candidate = &candidates[idx];
+            let window = windows[idx];
+            let Some(path) =
+                self.animations
+                    .phased_route_to(candidate.node_id, window.to, now_nsec)
+            else {
+                return false;
+            };
+            paths.push(path);
+        }
+        let plan = match validate_phase_paths(request, &paths) {
+            Ok(plan) => plan,
+            Err(error) => {
+                log::debug!(
+                    "existing phased retarget rejected for group {:?}: {:?}",
+                    group,
+                    error
+                );
+                return false;
+            }
+        };
+        log::debug!("retargeting active phased animation for group {:?}", group);
+        self.start_multiphase_plan(candidates, windows, group, &plan.phases, now_nsec)
+    }
+
+    fn start_multiphase_plan(
+        self: &Rc<Self>,
+        candidates: &[LayoutAnimationCandidate],
+        windows: &[MultiphaseWindow],
+        group: &[usize],
+        plan_phases: &[crate::animation::multiphase::MultiphasePhase],
+        now_nsec: u64,
+    ) -> bool {
+        if plan_phases.is_empty() {
             return false;
         }
         let mut entries = vec![];
@@ -1700,7 +1749,7 @@ impl State {
             let mut current = window.from;
             let mut damage = current.union(window.to);
             let mut phases = vec![];
-            for phase in &plan.phases {
+            for phase in plan_phases {
                 match phase
                     .steps
                     .iter()