Skip tiny swap redistribution phases

src/animation/multiphase.rs

@@ -1,6 +1,9 @@
 use {crate::rect::Rect, crate::tree::NodeId};
 
 const MIN_SHRINK_DENOMINATOR: i32 = 8;
+// Integer split remainders can make swapped siblings differ by one pixel. Do
+// not spend a full animation phase on that imperceptible bookkeeping step.
+const SWAP_AXIS_SNAP_PX: i32 = 1;
 
 #[derive(Clone, Debug)]
 pub struct MultiphaseRequest {
@@ -876,7 +879,10 @@ fn plan_axis_crossing_lanes(
             main_start(window.to, axis),
             main_end(window.to, axis),
         );
-        let lane_move = crossing_lane_move_rect(lane_from, window.to, axis);
+        let mut lane_move = crossing_lane_move_rect(lane_from, window.to, axis);
+        if same_axis_delta_within(lane_move, lane_to, axis, SWAP_AXIS_SNAP_PX) {
+            lane_move = lane_to;
+        }
         push_step(&mut phase1, window.node_id, window.from, lane_from);
         push_step(&mut phase2, window.node_id, lane_from, lane_move);
         push_step(&mut phase3, window.node_id, lane_move, lane_to);
@@ -897,12 +903,10 @@ fn plan_axis_crossing_lanes(
                     lane_axis: axis.other(),
                 },
             ),
-            phase_draft(
-                PhaseKind::Move,
-                axis,
+            phase_draft_classified(
                 phase2,
                 PhaseReason::MoveThroughFreedSpace,
-            ),
+            )?,
             phase_draft(
                 PhaseKind::Scale,
                 axis,
@@ -919,6 +923,17 @@ fn plan_axis_crossing_lanes(
     )
 }
 
+fn phase_draft_classified(
+    steps: Vec<MultiphaseStep>,
+    reason: PhaseReason,
+) -> Result<MultiphasePhaseDraft, MultiphasePlanFailure> {
+    let actions = steps
+        .iter()
+        .map(|step| classify_step(*step).ok_or(MultiphasePlanFailure::NoPattern))
+        .collect::<Result<Vec<_>, _>>()?;
+    Ok(phase_draft_mixed(steps, actions, reason))
+}
+
 fn crossing_lane_move_rect(from: Rect, target: Rect, axis: PhaseAxis) -> Rect {
     let size = main_size(from, axis);
     if main_start(target, axis) > main_start(from, axis) {
@@ -930,6 +945,12 @@ fn crossing_lane_move_rect(from: Rect, target: Rect, axis: PhaseAxis) -> Rect {
     }
 }
 
+fn same_axis_delta_within(from: Rect, to: Rect, axis: PhaseAxis, max_delta: i32) -> bool {
+    let start_delta = (main_start(from, axis) - main_start(to, axis)).abs();
+    let end_delta = (main_end(from, axis) - main_end(to, axis)).abs();
+    start_delta.max(end_delta) <= max_delta
+}
+
 fn lane_sort_key(window: MultiphaseWindow, axis: PhaseAxis) -> (usize, i32, i32, u32) {
     let delta = main_start(window.to, axis) - main_start(window.from, axis);
     let direction = match delta.cmp(&0) {
@@ -2092,7 +2113,7 @@ mod tests {
     }
 
     #[test]
-    fn uneven_swap_lanes_split_move_and_same_axis_scale() {
+    fn one_pixel_uneven_swap_lanes_fold_remainder_into_crossing_phase() {
         let req = request(vec![
             window(1, rect(0, 0, 101, 100), rect(101, 0, 201, 100)),
             window(2, rect(101, 0, 201, 100), rect(0, 0, 101, 100)),
@@ -2100,6 +2121,43 @@ mod tests {
         let planned = plan_no_overlap_explained(&req).unwrap();
         let plan = &planned.plan;
 
+        assert_eq!(
+            planned.explanation.strategy,
+            PlanStrategy::SwapLanes {
+                axis: PhaseAxis::Horizontal,
+            }
+        );
+        assert_eq!(
+            actions(plan),
+            vec![
+                PhaseAction {
+                    kind: PhaseKind::Scale,
+                    axis: PhaseAxis::Vertical,
+                },
+                PhaseAction {
+                    kind: PhaseKind::Scale,
+                    axis: PhaseAxis::Horizontal,
+                },
+                PhaseAction {
+                    kind: PhaseKind::Scale,
+                    axis: PhaseAxis::Vertical,
+                },
+            ]
+        );
+        assert_eq!(step_to(plan, 1, id(1)), rect(101, 0, 201, 50));
+        assert_eq!(step_to(plan, 1, id(2)), rect(0, 50, 101, 100));
+        assert!(validate_plan_continuous(&req, plan));
+    }
+
+    #[test]
+    fn large_uneven_swap_lanes_split_move_and_same_axis_scale() {
+        let req = request(vec![
+            window(1, rect(0, 0, 120, 100), rect(120, 0, 200, 100)),
+            window(2, rect(120, 0, 200, 100), rect(0, 0, 120, 100)),
+        ]);
+        let planned = plan_no_overlap_explained(&req).unwrap();
+        let plan = &planned.plan;
+
         assert_eq!(
             planned.explanation.strategy,
             PlanStrategy::SwapLanes {
@@ -2127,10 +2185,10 @@ mod tests {
                 },
             ]
         );
-        assert_eq!(step_to(plan, 1, id(1)), rect(100, 0, 201, 50));
-        assert_eq!(step_to(plan, 1, id(2)), rect(0, 50, 100, 100));
-        assert_eq!(step_to(plan, 2, id(1)), rect(101, 0, 201, 50));
-        assert_eq!(step_to(plan, 2, id(2)), rect(0, 50, 101, 100));
+        assert_eq!(step_to(plan, 1, id(1)), rect(80, 0, 200, 50));
+        assert_eq!(step_to(plan, 1, id(2)), rect(0, 50, 80, 100));
+        assert_eq!(step_to(plan, 2, id(1)), rect(120, 0, 200, 50));
+        assert_eq!(step_to(plan, 2, id(2)), rect(0, 50, 120, 100));
         assert!(validate_plan_continuous(&req, plan));
     }
 
@@ -2149,6 +2207,23 @@ mod tests {
                 axis: PhaseAxis::Horizontal,
             }
         );
+        assert_eq!(
+            actions(&planned.plan),
+            vec![
+                PhaseAction {
+                    kind: PhaseKind::Scale,
+                    axis: PhaseAxis::Vertical,
+                },
+                PhaseAction {
+                    kind: PhaseKind::Scale,
+                    axis: PhaseAxis::Horizontal,
+                },
+                PhaseAction {
+                    kind: PhaseKind::Scale,
+                    axis: PhaseAxis::Vertical,
+                },
+            ]
+        );
         assert!(validate_plan_continuous(&req, &planned.plan));
     }