perf: cache node z-indexes before legacy sorting

Amp-Thread-ID: https://ampcode.com/threads/T-01a02705-02f3-70c9-ae5b-8ea6c2a3cac2

Author: ampagent

src/renderer/core/canvas/litegraph/arrangeForLegacyRender.test.ts

@@ -1,10 +1,11 @@
 import { createTestingPinia } from '@pinia/testing'
 import { setActivePinia } from 'pinia'
-import { afterEach, beforeEach, describe, expect, it } from 'vitest'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
 import { LGraph, LGraphNode, LiteGraph } from '@/lib/litegraph/src/litegraph'
 import { arrangeForLegacyRender } from '@/renderer/core/canvas/litegraph/arrangeForLegacyRender'
 import { useLayoutMutations } from '@/renderer/core/layout/operations/layoutMutations'
+import { layoutStore } from '@/renderer/core/layout/store/layoutStore'
 import { LayoutSource } from '@/renderer/core/layout/types'
 
 function addedNode(graph: LGraph) {
@@ -60,4 +61,15 @@ describe('arrangeForLegacyRender', () => {
 
     expect(graph._nodes).toEqual([second, first])
   })
+
+  it('reads each node layout once while sorting', () => {
+    const graph = new LGraph()
+    const nodes = [addedNode(graph), addedNode(graph), addedNode(graph)]
+    for (const node of nodes) node.flags.collapsed = true
+    const getNodeLayout = vi.spyOn(layoutStore, 'getNodeLayout')
+
+    arrangeForLegacyRender(graph)
+
+    expect(getNodeLayout).toHaveBeenCalledTimes(nodes.length)
+  })
 })

src/renderer/core/canvas/litegraph/arrangeForLegacyRender.ts

@@ -14,10 +14,14 @@ const logger = log.getLogger('arrangeForLegacyRender')
  */
 export function arrangeForLegacyRender(graph: LGraph): void {
   const rootGraphId = graph.rootGraph.id
+  const zIndexByNode = new Map(
+    graph._nodes.map((node) => [
+      node,
+      layoutStore.getNodeLayout(rootGraphId, node.id)?.zIndex ?? 0
+    ])
+  )
   graph._nodes.sort(
-    (a, b) =>
-      (layoutStore.getNodeLayout(rootGraphId, a.id)?.zIndex ?? 0) -
-      (layoutStore.getNodeLayout(rootGraphId, b.id)?.zIndex ?? 0)
+    (a, b) => (zIndexByNode.get(a) ?? 0) - (zIndexByNode.get(b) ?? 0)
   )
 
   for (const node of graph._nodes) {