fix(line): respect disabled emphasis in hover. close #21634

[rahul37wallst-sudo]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Respect disabled emphasis for line-series tooltip hover symbols.

Fixed issues

• [Bug] ECharts 6.1.0 canvas dirty-rect repaint corrupts dense line series on tooltip axis-pointer hover #21634: Fix dirty-rect repaint corruption for dense canvas line series with tooltip axis-pointer hover.

Details

Before: What was the problem?

For dense canvas line series with showSymbol: false, useDirtyRect: true,
tooltip axis-pointer hover, and emphasis: { disabled: true },
LineView.highlight() could still create a temporary hover symbol.

That temporary symbol was later removed during downplay. The add/remove
lifecycle could leave stale or corrupted line pixels when dirty-rect repainting
was enabled.

This reproduced with the issue's ECharts 6.1.0 canvas scenario:

• dense line series
• showSymbol: false
• progressive
• piecewise visualMap
• tooltip trigger: 'axis'
• tooltip axis pointer
• useDirtyRect: true
• emphasis: { disabled: true }

After: How does it behave after the fixing?

When line-series emphasis is disabled, LineView.highlight() no longer creates
or highlights a temporary hover symbol, and downplay() avoids symbol/whole
series downplay work for disabled emphasis.

The existing polyline state transition is kept so dirty-rect invalidation still
clears tooltip axis-pointer updates correctly.

Verified with a pixel-diff harness comparing a dirty-rect chart against a
full-repaint control:

• native mouse hover: 0 mismatches
• showTip action: 0 mismatches
• settled after hideTip: 0 mismatches

Also passed:

npm run lint
npm run checktype

Document Info

One of the following should be checked.

• 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

N.A.

Merging options

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

Other information

This fix was investigated together with ecomfe/zrender#1159. The ZRender
dirty-rect changes improved related behavior but did not fully resolve this
ECharts-side temp-symbol path. The final fix here is independent of ZRender
changes.

[echarts-bot]

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