fix(dataZoom): keep boundary neighbors for line series so partial segments and null gaps survive

[JamesGoslings]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

When dataZoom filters a line series with the default filterMode: 'filter', keep one neighboring data row on each side of the in-window range so partial line segments at the boundary can still be drawn and null gap markers outside the window still interrupt the line.

Fixed issues

• close [Bug] Line chart drops partially visible lines entirely #21564
• close [Bug] Interrupted lines can draw ghost lines #21565

Details

Before: What was the problem?

Both bugs share one root cause. AxisProxy.filterData() calls seriesData.selectRange(), which physically drops every row whose value falls outside the data zoom window. For line / area series this corrupts the rendering in two ways:

#21564 — partial line segments vanish at the boundary.
When a segment connects an in-window point with an out-of-window point, the out-of-window endpoint is removed and the line view loses the entire segment instead of clipping it. The result is that any line crossing the visible edge disappears completely.

#21565 — null gap markers stop interrupting the line.
When a null row's value sits outside the window, the row is dropped from the filtered store and the line view never sees the gap marker. With non-monotonic data, the line view then connects two rows that should remain interrupted, drawing a "ghost line".

After: How does it behave after the fixing?

For line / area series only (subType === 'line') and only when filterMode === 'filter', swap selectRange() for a boundary-aware filter:

Keep row i if row i, row i-1 or row i+1 is in the window.

A single Uint8Array pre-scan computes inWindow status; filterSelf then applies the keep predicate in one pass. Other series types (bar, scatter, ...) and other filter modes (none, empty, weakFilter) are completely untouched, so the fast selectRange path remains the default for everything that does not need this.

With the fix:

• The boundary points just outside the window are retained, so segments crossing the edge still draw their visible portion (clip path takes care of the cropping).
• A null row whose raw-order neighbor is in the window is retained, so it still breaks the line and prevents ghost connections.

The visible-y extent on auto-fit Y axes may extend slightly to include the boundary points' Y values; this is necessary because the partial segment's clipping line can reach those Y values, and without the wider extent the segment would be clipped along the Y dimension as well.

Tests

test/ut/spec/component/dataZoom/lineBoundary.test.ts adds five unit tests covering:

• #21564: window [3, 13] against [(0,5), (2,6), (8,5), (12,5), (16,6)] → kept raw indices [1, 2, 3, 4] (the two boundary neighbors are now retained).
• #21565: window [3, 10] against [(4,5), (7,5), (11,5), (11,null), (6,6), (9,6)] → all six rows retained, so the null still breaks the line.
• bar series: behavior unchanged (no boundary keeping).
• filterMode: 'none': behavior unchanged.
• All-in-window: short-circuited, no extra work.

test/line-dataZoom-boundary.html is a visual reproducer for both issues so reviewers can pan the chart and verify the rendering directly.

Full unit suite: 26 suites, 197 tests, all green.

Document Info

• This PR doesn't relate to document changes
• The document should be updated later
• The document changes have been made in apache/echarts-doc#xxx

Misc

Security Checking

• This PR uses security-sensitive Web APIs.

ZRender Changes

• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Related test cases or examples to use the new APIs

• test/ut/spec/component/dataZoom/lineBoundary.test.ts — unit tests
• test/line-dataZoom-boundary.html — visual reproducer

Merging options

• Please squash the commits into a single one when merging.

Other information

A few related rendering features were not exhaustively visually verified and are worth a reviewer's eye:

• endLabel on a line series with dataZoom: with the fix, the last filtered row may be a boundary point sitting just outside the window. The label would either be clipped or rendered just past the chart edge depending on how endLabel is positioned. If this turns out to need adjusting, it can be a follow-up.
• markPoint with type: 'max' / 'min': same caveat — these may now match a boundary point.

For the bugs as reported, both reproductions render correctly with the fix applied.

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