From 02222d5189abf563206e8abbb7accb4e2b1264cf Mon Sep 17 00:00:00 2001
From: atagen <boss@atagen.co>
Date: Wed, 27 May 2026 22:24:01 +1000
Subject: [PATCH] Coalesce layout animation candidates

---
 src/state.rs | 152 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 152 insertions(+)

diff --git a/src/state.rs b/src/state.rs
index bf806640..071a054d 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -171,6 +171,28 @@ pub(crate) struct LayoutAnimationCandidate {
     hierarchy: MultiphaseWindowHierarchy,
 }
 
+fn coalesce_layout_animation_candidates(
+    candidates: Vec<LayoutAnimationCandidate>,
+) -> Vec<LayoutAnimationCandidate> {
+    let mut merged: Vec<LayoutAnimationCandidate> = vec![];
+    for candidate in candidates {
+        if let Some(existing) = merged
+            .iter_mut()
+            .find(|existing| existing.node_id == candidate.node_id)
+        {
+            existing.new = candidate.new;
+            existing.curve = candidate.curve;
+            existing.hierarchy = MultiphaseWindowHierarchy::new(
+                existing.hierarchy.source,
+                candidate.hierarchy.target,
+            );
+        } else {
+            merged.push(candidate);
+        }
+    }
+    merged
+}
+
 pub struct State {
     pub pid: c::pid_t,
     pub kb_ctx: KbvmContext,
@@ -1619,6 +1641,10 @@ impl State {
         let Some(candidates) = self.layout_animation_batch.borrow_mut().take() else {
             return;
         };
+        let candidates = coalesce_layout_animation_candidates(candidates);
+        if candidates.is_empty() {
+            return;
+        }
         let now = self.now_nsec();
         let windows: Vec<_> = candidates
             .iter()
@@ -2431,6 +2457,132 @@ impl State {
     }
 }
 
+#[cfg(test)]
+mod tests {
+    use {
+        super::*,
+        crate::animation::multiphase::MultiphaseHierarchyPosition,
+    };
+
+    fn rect(x1: i32, y1: i32, x2: i32, y2: i32) -> Rect {
+        Rect::new_saturating(x1, y1, x2, y2)
+    }
+
+    fn hierarchy(
+        source: MultiphaseHierarchyPosition,
+        target: MultiphaseHierarchyPosition,
+    ) -> MultiphaseWindowHierarchy {
+        MultiphaseWindowHierarchy::new(source, target)
+    }
+
+    #[test]
+    fn layout_animation_candidates_coalesce_duplicate_nodes() {
+        let source = MultiphaseHierarchyPosition {
+            parent: Some(NodeId(10)),
+            depth: 2,
+            sibling_index: Some(1),
+            ..Default::default()
+        };
+        let intermediate = MultiphaseHierarchyPosition {
+            parent: Some(NodeId(11)),
+            depth: 1,
+            sibling_index: Some(0),
+            ..Default::default()
+        };
+        let target = MultiphaseHierarchyPosition {
+            parent: Some(NodeId(12)),
+            depth: 0,
+            sibling_index: Some(2),
+            ..Default::default()
+        };
+        let second_source = MultiphaseHierarchyPosition {
+            parent: Some(NodeId(20)),
+            depth: 1,
+            sibling_index: Some(0),
+            ..Default::default()
+        };
+        let second_target = MultiphaseHierarchyPosition {
+            parent: Some(NodeId(20)),
+            depth: 1,
+            sibling_index: Some(1),
+            ..Default::default()
+        };
+
+        let candidates = vec![
+            LayoutAnimationCandidate {
+                node_id: NodeId(1),
+                old: rect(0, 0, 100, 100),
+                new: rect(0, 0, 80, 100),
+                curve: AnimationCurve::Linear,
+                hierarchy: hierarchy(source, intermediate),
+            },
+            LayoutAnimationCandidate {
+                node_id: NodeId(2),
+                old: rect(100, 0, 200, 100),
+                new: rect(120, 0, 220, 100),
+                curve: AnimationCurve::Linear,
+                hierarchy: hierarchy(second_source, second_target),
+            },
+            LayoutAnimationCandidate {
+                node_id: NodeId(1),
+                old: rect(0, 0, 80, 100),
+                new: rect(0, 0, 60, 100),
+                curve: AnimationCurve::from_config(4),
+                hierarchy: hierarchy(intermediate, target),
+            },
+        ];
+
+        let merged = coalesce_layout_animation_candidates(candidates);
+
+        assert_eq!(merged.len(), 2);
+        assert_eq!(merged[0].node_id, NodeId(1));
+        assert_eq!(merged[0].old, rect(0, 0, 100, 100));
+        assert_eq!(merged[0].new, rect(0, 0, 60, 100));
+        assert_eq!(merged[0].curve, AnimationCurve::from_config(4));
+        assert_eq!(merged[0].hierarchy, hierarchy(source, target));
+        assert_eq!(merged[1].node_id, NodeId(2));
+        assert_eq!(merged[1].old, rect(100, 0, 200, 100));
+        assert_eq!(merged[1].new, rect(120, 0, 220, 100));
+        assert_eq!(merged[1].hierarchy, hierarchy(second_source, second_target));
+    }
+
+    #[test]
+    fn layout_animation_candidates_keep_coalesced_layout_noops() {
+        let hierarchy = MultiphaseWindowHierarchy::default();
+        let candidates = vec![
+            LayoutAnimationCandidate {
+                node_id: NodeId(1),
+                old: rect(0, 0, 100, 100),
+                new: rect(0, 0, 80, 100),
+                curve: AnimationCurve::Linear,
+                hierarchy,
+            },
+            LayoutAnimationCandidate {
+                node_id: NodeId(1),
+                old: rect(0, 0, 80, 100),
+                new: rect(0, 0, 100, 100),
+                curve: AnimationCurve::Linear,
+                hierarchy,
+            },
+            LayoutAnimationCandidate {
+                node_id: NodeId(2),
+                old: rect(100, 0, 200, 100),
+                new: rect(120, 0, 220, 100),
+                curve: AnimationCurve::Linear,
+                hierarchy,
+            },
+        ];
+
+        let merged = coalesce_layout_animation_candidates(candidates);
+
+        assert_eq!(merged.len(), 2);
+        assert_eq!(merged[0].node_id, NodeId(1));
+        assert_eq!(merged[0].old, rect(0, 0, 100, 100));
+        assert_eq!(merged[0].new, rect(0, 0, 100, 100));
+        assert_eq!(merged[1].node_id, NodeId(2));
+    }
+}
+
 #[derive(Debug, Error)]
 pub enum ShmScreencopyError {
     #[error("There is no render context")]