fix(stacked): Fix stacked area chart drawing on zero value

[seekskyworld]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

This PR fixes a bug where stacked area charts with stackStrategy: 'samesign' incorrectly draw an area for data points with a value of 0 by strictly excluding 0 from the stacking logic.

Fixed issues

• Fixes [Bug] Stacked Area Chart draw the area even though the value is 0. #21467

Details

Before: What was the problem?

When stackStrategy is set to 'samesign', the previous implementation treated 0 as a positive value (using a >= 0 check). This caused zero-value points to be stacked on top of the previous series instead of being treated independently. As a result, the chart would render a visual area for the zero value, which is incorrect behavior for a stacked area chart.

After: How does it behave after the fixing?

The stacking logic in src/processor/dataStack.ts has been updated to strictly check for positive (> 0) or negative (< 0) values when using samesign. Zero values are no longer considered part of the stack group. This ensures that no area is drawn for 0 values, providing the correct visual representation.

Validation:

• A new unit test has been added to test/ut/spec/processor/dataStack.test.ts to verify that 0 values result in NaN for stackedOverDimension.
• A manual test case test/issue-21467.html has been added for visual verification.

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

[echarts-bot]

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