组件内部 zIndex 抬升子树排序键，根级浮层（scrim/下拉菜单）失去命中与绘制优先级
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Assessment
- Difficulty
- 2/5
- Estimated time
- Under an hour
- Newbie friendliness
- 78/100
- Issue type
- Bug
- Clarity
- Clearly specified
- Activity status
- Active
- Tech stack
- cpp
- Domain
- desktop-dev
Research direction
Start in components/slider.h, where the .hit rect is built with a hard-coded zIndex, and check how rebuildOrderedElements in core/dsl.h sorts children by subtreeMaxZIndex. The regression test is tests/unit/slider_subtree_z_order.cpp; build and run it first to see the failing assertion. Done when page->subtreeMaxZIndex is 0 and the overlay sorts after the page, so the test passes without changing other slider behavior.
Written by the indexing model from the issue text.
Description
现象
宿主应用（节点编辑器画布）中，页面内容包含滑条组件后，合成在其后的根级浮层——全窗口 scrim 与下拉菜单面板——完全失去命中优先级：点击 scrim/菜单项时，事件落到页面底层的输入区（画布 mouseArea），浮层被意外收起、菜单项永远无法选中。绘制序同样被压到页面之下。
宿主真机 A/B 实证（同一画布、同一浮层代码，唯一变量是页面内是否存在滑条参数节点）：
- 页面含滑条节点 → 点击浮层菜单项的坐标，事件穿透到画布输入区；
- 页面不含滑条节点（无参数的节点）→ 同一坐标由 scrim 正确拦截并收起浮层。
根因
命中测试与绘制的遍历顺序按 orderedChildren / orderedRoots 排序，排序键是 subtreeMaxZIndex（core/dsl.h 的 rebuildOrderedElements，升序排序、命中逆序遍历）。
而 components/slider.h 的内部热区自带硬编码 zIndex：
ui_.rect(id_ + ".hit")
.size(width_, height_)
.states(...)
.zIndex(10) // ← 抬升整个滑条子树的排序键
.interactive()
.sliderInputFrom(id_)
.build();
滑条栈内 .hit 的输入优先级本就由合成序保证（栈内最后一个子元素，逆序命中时最先被测试），这个 zIndex(10) 没有栈内收益，却把页面子树的 max z 抬到 10——所有默认 z=0 的根级浮层在根级兄弟排序中被排到页面之后（命中先测试页面、绘制后画页面），浮层即失效。
两个连带推论：
- 由于排序只看 z 不看合成序，浮层即便晚于页面合成也无法挽回；
- 同理，滑条所在子树还会压过其后合成的兄弟子树中 z=0 的交互元素（如后画到滑条上方的卡片控件），不只是根级浮层场景。
最小复现（单元级）
root stack → page stack（内含一个 components::slider）→ overlay rect（onClick，z 默认 0，后合成）。
ui.layout(...) 后：page->subtreeMaxZIndex == 10，且 root 的 orderedChildren 中 overlay 被排到 page 之前——逆序命中遍历先测 page。修复后两者均为 0、稳定序保持合成序（overlay 在后，逆序命中先达）。
（已随修复提交回归测试 tests/unit/slider_subtree_z_order.cpp：修复前该测试在第一条断言失败——slider inflates page subtreeMaxZIndex to 10。）
影响
凡页面内容包含滑条，宿主的模态浮层（下拉、右键菜单、scrim）、以及页面上后合成的 z=0 交互控件，命中与绘制都被滑条子树压过。组件库若未来有更多组件内部使用 zIndex，同类风险会扩大。
建议修复
移除 slider.h .hit 的 .zIndex(10)（其栈内优先级由合成序保证，行为不变）。随后提 PR，附上述回归测试。
- Dominant language
- C++
- Stars
- 2k
- Forks
- 177
- Avg merge
- 19h 58m
- Merged PRs (30d)
- 9
Getting set up
This project ships no dev container, Dockerfile or contributing guide, so setting up is up to you: start from its README, and see our first-contribution guide for the general steps.
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
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