Validate multiphase overlap analytically

docs/window-animations-plan.md

@@ -220,7 +220,9 @@ Current pure planner status:
 - Stack extraction/return patterns are covered in both horizontal and vertical
   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.
+- Every produced plan is checked analytically for overlap over the full duration
+  of each phase before it is accepted. This solves the linear edge inequalities
+  for each pair of moving rectangles instead of relying on sampled frames.
 - 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.

src/animation/multiphase.rs

@@ -1,7 +1,6 @@
 use {crate::rect::Rect, crate::tree::NodeId};
 
 const MIN_SHRINK_DENOMINATOR: i32 = 4;
-const PHASE_VALIDATION_SAMPLES: [f64; 5] = [0.0, 0.25, 0.5, 0.75, 1.0];
 
 #[derive(Clone, Debug)]
 pub struct MultiphaseRequest {
@@ -288,10 +287,10 @@ fn build_validated_plan<const N: usize>(
         return None;
     }
     let plan = MultiphasePlan { phases };
-    validate_plan_samples(request, &plan).then_some(plan)
+    validate_plan_continuous(request, &plan).then_some(plan)
 }
 
-fn validate_plan_samples(request: &MultiphaseRequest, plan: &MultiphasePlan) -> bool {
+fn validate_plan_continuous(request: &MultiphaseRequest, plan: &MultiphasePlan) -> bool {
     let mut current: Vec<_> = request
         .windows
         .iter()
@@ -301,26 +300,46 @@ fn validate_plan_samples(request: &MultiphaseRequest, plan: &MultiphasePlan) ->
         return false;
     }
     for phase in &plan.phases {
-        for t in PHASE_VALIDATION_SAMPLES {
-            let rects = current.iter().map(|(node_id, rect)| {
-                phase
+        for (idx, step) in phase.steps.iter().enumerate() {
+            if phase.steps[..idx]
+                .iter()
+                .any(|prev| prev.node_id == step.node_id)
+            {
+                return false;
+            }
+            let Some((_, rect)) = current.iter().find(|(node_id, _)| *node_id == step.node_id)
+            else {
+                return false;
+            };
+            if *rect != step.from {
+                return false;
+            }
+        }
+        let motions: Vec<_> = current
+            .iter()
+            .map(|(node_id, rect)| {
+                let to = phase
                     .steps
                     .iter()
                     .find(|step| step.node_id == *node_id)
-                    .map(|step| super::lerp_rect(step.from, step.to, t))
-                    .unwrap_or(*rect)
-            });
-            if overlaps(rects) {
+                    .map(|step| step.to)
+                    .unwrap_or(*rect);
+                RectMotion { from: *rect, to }
+            })
+            .collect();
+        for (idx, motion) in motions.iter().enumerate() {
+            if motions[idx + 1..]
+                .iter()
+                .any(|other| motions_overlap_during_phase(*motion, *other))
+            {
                 return false;
             }
         }
         for step in &phase.steps {
-            let Some((_, rect)) = current
+            let (_, rect) = current
                 .iter_mut()
                 .find(|(node_id, _)| *node_id == step.node_id)
-            else {
-                return false;
-            };
+                .unwrap();
             *rect = step.to;
         }
         if overlaps(current.iter().map(|(_, rect)| *rect)) {
@@ -335,6 +354,122 @@ fn validate_plan_samples(request: &MultiphaseRequest, plan: &MultiphasePlan) ->
     })
 }
 
+#[derive(Copy, Clone)]
+struct RectMotion {
+    from: Rect,
+    to: Rect,
+}
+
+fn motions_overlap_during_phase(a: RectMotion, b: RectMotion) -> bool {
+    let mut interval = TimeInterval::unit();
+    interval.intersect_less_than(edge_delta(a.from.x1(), a.to.x1(), b.from.x2(), b.to.x2()))
+        && interval.intersect_less_than(edge_delta(b.from.x1(), b.to.x1(), a.from.x2(), a.to.x2()))
+        && interval.intersect_less_than(edge_delta(a.from.y1(), a.to.y1(), b.from.y2(), b.to.y2()))
+        && interval.intersect_less_than(edge_delta(b.from.y1(), b.to.y1(), a.from.y2(), a.to.y2()))
+        && interval.is_non_empty()
+}
+
+fn edge_delta(a0: i32, a1: i32, b0: i32, b1: i32) -> LinearDelta {
+    let from = a0 as i64 - b0 as i64;
+    let to = a1 as i64 - b1 as i64;
+    LinearDelta {
+        start: from,
+        velocity: to - from,
+    }
+}
+
+#[derive(Copy, Clone)]
+struct LinearDelta {
+    start: i64,
+    velocity: i64,
+}
+
+#[derive(Copy, Clone)]
+struct TimeInterval {
+    lower: Rational,
+    lower_open: bool,
+    upper: Rational,
+    upper_open: bool,
+}
+
+impl TimeInterval {
+    fn unit() -> Self {
+        Self {
+            lower: Rational::new(0, 1),
+            lower_open: false,
+            upper: Rational::new(1, 1),
+            upper_open: false,
+        }
+    }
+
+    fn intersect_less_than(&mut self, delta: LinearDelta) -> bool {
+        if delta.velocity == 0 {
+            return delta.start < 0;
+        }
+        let boundary = Rational::new(-delta.start, delta.velocity);
+        if delta.velocity > 0 {
+            self.tighten_upper(boundary, true);
+        } else {
+            self.tighten_lower(boundary, true);
+        }
+        self.is_non_empty()
+    }
+
+    fn tighten_lower(&mut self, value: Rational, open: bool) {
+        match value.cmp(&self.lower) {
+            std::cmp::Ordering::Greater => {
+                self.lower = value;
+                self.lower_open = open;
+            }
+            std::cmp::Ordering::Equal => {
+                self.lower_open |= open;
+            }
+            std::cmp::Ordering::Less => {}
+        }
+    }
+
+    fn tighten_upper(&mut self, value: Rational, open: bool) {
+        match value.cmp(&self.upper) {
+            std::cmp::Ordering::Less => {
+                self.upper = value;
+                self.upper_open = open;
+            }
+            std::cmp::Ordering::Equal => {
+                self.upper_open |= open;
+            }
+            std::cmp::Ordering::Greater => {}
+        }
+    }
+
+    fn is_non_empty(&self) -> bool {
+        match self.lower.cmp(&self.upper) {
+            std::cmp::Ordering::Less => true,
+            std::cmp::Ordering::Equal => !self.lower_open && !self.upper_open,
+            std::cmp::Ordering::Greater => false,
+        }
+    }
+}
+
+#[derive(Copy, Clone, Eq, PartialEq)]
+struct Rational {
+    num: i64,
+    den: i64,
+}
+
+impl Rational {
+    fn new(mut num: i64, mut den: i64) -> Self {
+        if den < 0 {
+            num = -num;
+            den = -den;
+        }
+        Self { num, den }
+    }
+
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        (self.num as i128 * other.den as i128).cmp(&(other.num as i128 * self.den as i128))
+    }
+}
+
 fn classify_step(step: MultiphaseStep) -> Option<PhaseAction> {
     let same_x = step.from.x1() == step.to.x1() && step.from.x2() == step.to.x2();
     let same_y = step.from.y1() == step.to.y1() && step.from.y2() == step.to.y2();
@@ -526,7 +661,7 @@ mod tests {
         );
         assert_eq!(plan.phases[0].steps[0].to, rect(0, 0, 100, 50));
         assert_eq!(plan.phases[0].steps[1].to, rect(100, 50, 200, 100));
-        assert!(validate_plan_samples(&req, &plan));
+        assert!(validate_plan_continuous(&req, &plan));
     }
 
     #[test]
@@ -546,7 +681,7 @@ mod tests {
         let plan = plan_no_overlap(&req).unwrap();
         assert_eq!(plan.phases[0].steps[0].to, rect(100, 0, 200, 50));
         assert_eq!(plan.phases[0].steps[1].to, rect(0, 50, 100, 100));
-        assert!(validate_plan_samples(&req, &plan));
+        assert!(validate_plan_continuous(&req, &plan));
     }
 
     #[test]
@@ -591,7 +726,7 @@ mod tests {
         assert_eq!(plan.phases[1].steps[0].to, rect(100, 0, 300, 50));
         assert_eq!(plan.phases[2].steps[0].to, rect(100, 0, 300, 100));
         assert_eq!(plan.phases[2].steps[1].to, rect(300, 0, 400, 100));
-        assert!(validate_plan_samples(&req, &plan));
+        assert!(validate_plan_continuous(&req, &plan));
     }
 
     #[test]
@@ -631,7 +766,7 @@ mod tests {
                 },
             ]
         );
-        assert!(validate_plan_samples(&req, &plan));
+        assert!(validate_plan_continuous(&req, &plan));
     }
 
     #[test]
@@ -676,7 +811,7 @@ mod tests {
         assert_eq!(plan.phases[1].steps[0].to, rect(0, 100, 50, 300));
         assert_eq!(plan.phases[2].steps[0].to, rect(0, 100, 100, 300));
         assert_eq!(plan.phases[2].steps[1].to, rect(0, 300, 100, 400));
-        assert!(validate_plan_samples(&req, &plan));
+        assert!(validate_plan_continuous(&req, &plan));
     }
 
     #[test]
@@ -716,7 +851,7 @@ mod tests {
                 },
             ]
         );
-        assert!(validate_plan_samples(&req, &plan));
+        assert!(validate_plan_continuous(&req, &plan));
     }
 
     #[test]
@@ -729,6 +864,92 @@ mod tests {
         assert_eq!(plan_no_overlap(&req), Err(MultiphaseError::NoPlan));
     }
 
+    #[test]
+    fn continuous_validation_rejects_narrow_mid_phase_overlap() {
+        let req = request(vec![
+            MultiphaseWindow {
+                node_id: id(1),
+                from: rect(0, 0, 10, 10),
+                to: rect(100, 0, 110, 10),
+            },
+            MultiphaseWindow {
+                node_id: id(2),
+                from: rect(13, 0, 14, 10),
+                to: rect(13, 0, 14, 10),
+            },
+        ]);
+        let plan = MultiphasePlan {
+            phases: vec![MultiphasePhase {
+                action: PhaseAction {
+                    kind: PhaseKind::Move,
+                    axis: PhaseAxis::Horizontal,
+                },
+                steps: vec![MultiphaseStep {
+                    node_id: id(1),
+                    from: rect(0, 0, 10, 10),
+                    to: rect(100, 0, 110, 10),
+                }],
+            }],
+        };
+
+        assert!(!validate_plan_continuous(&req, &plan));
+    }
+
+    #[test]
+    fn continuous_validation_allows_edge_touching_motion() {
+        let req = request(vec![
+            MultiphaseWindow {
+                node_id: id(1),
+                from: rect(0, 0, 10, 10),
+                to: rect(10, 0, 20, 10),
+            },
+            MultiphaseWindow {
+                node_id: id(2),
+                from: rect(20, 0, 30, 10),
+                to: rect(20, 0, 30, 10),
+            },
+        ]);
+        let plan = MultiphasePlan {
+            phases: vec![MultiphasePhase {
+                action: PhaseAction {
+                    kind: PhaseKind::Move,
+                    axis: PhaseAxis::Horizontal,
+                },
+                steps: vec![MultiphaseStep {
+                    node_id: id(1),
+                    from: rect(0, 0, 10, 10),
+                    to: rect(10, 0, 20, 10),
+                }],
+            }],
+        };
+
+        assert!(validate_plan_continuous(&req, &plan));
+    }
+
+    #[test]
+    fn continuous_validation_rejects_stale_step_start_rect() {
+        let req = request(vec![MultiphaseWindow {
+            node_id: id(1),
+            from: rect(0, 0, 10, 10),
+            to: rect(20, 0, 30, 10),
+        }]);
+        let plan = MultiphasePlan {
+            phases: vec![MultiphasePhase {
+                action: PhaseAction {
+                    kind: PhaseKind::Move,
+                    axis: PhaseAxis::Horizontal,
+                },
+                steps: vec![MultiphaseStep {
+                    node_id: id(1),
+                    from: rect(5, 0, 15, 10),
+                    to: rect(20, 0, 30, 10),
+                }],
+            }],
+        };
+
+        assert!(!validate_plan_continuous(&req, &plan));
+    }
+
     #[test]
     fn motion_groups_split_disjoint_layout_changes() {
         let windows = vec![