perf(glass): complete phase three optimization (#580)

src/utils/scrollTarget.ts

@@ -0,0 +1,46 @@
+export type ScrollTarget = Window | HTMLElement
+
+let targetCache = new WeakMap<HTMLElement, ScrollTarget>()
+
+/**
+ * 清除祖先滚动容器缓存。响应式布局或 overlay 状态改变后必须重新解析。
+ */
+export function invalidateScrollTargetCache() {
+  targetCache = new WeakMap<HTMLElement, ScrollTarget>()
+}
+
+function isScrollableOverflow(overflowY: string) {
+  return overflowY === 'auto' || overflowY === 'scroll' || overflowY === 'overlay'
+}
+
+/**
+ * 解析元素最近的纵向滚动容器，并让同一祖先链上的网格复用样式查询结果。
+ */
+export function findNearestScrollTarget(element: HTMLElement | null): ScrollTarget {
+  if (!element) return window
+
+  let parent = element.parentElement
+  const visited: HTMLElement[] = []
+  let target: ScrollTarget = window
+
+  while (parent && parent !== document.body && parent !== document.documentElement) {
+    const cachedTarget = targetCache.get(parent)
+    if (cachedTarget) {
+      target = cachedTarget
+      break
+    }
+
+    visited.push(parent)
+
+    if (isScrollableOverflow(window.getComputedStyle(parent).overflowY)) {
+      target = parent
+      break
+    }
+
+    parent = parent.parentElement
+  }
+
+  visited.forEach(ancestor => targetCache.set(ancestor, target))
+
+  return target
+}