feat(chord): new chord series

[Ovilia]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Fixed issues

Details

The following are some highlights of the Chord implemented by this Pull Request.

Edges With Gradient

Other values include 'target' (using target color as edge color) and 'source' (using source color as edge color).

focus.emphasis Behaves Similar To Sankey

This is effect of focus: 'adjacency', which I use as the default value since it looks well and the interaction is more intuitive. Other values include 'none'and'self'`.

minAngle and padAngle

The current implementation of minAngle and padAngle have bugs with Pie Series (#20603) and Sunburst (#20602), so I re-implemented the logic in Chord Series. The bugs can be fixed with Pie and Sunburst in the future with the similar implementation of Chord.

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

ZRender Changes

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

Related test cases or examples to use the new APIs

N.A.

Others

Merging options

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

Other information

[echarts-bot]

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[github-actions]

The changes brought by this PR can be previewed at: https://echarts.apache.org/examples/editor?version=PR-20522@87599b5

[echarts-bot]

Document changes are required in this PR. Please also make a PR to apache/echarts-doc for document changes and update the issue id in the PR description. When the doc PR is merged, the maintainers will remove the PR: awaiting doc label.

[pissang]

It looks beautiful.

Curious about the decision that padAngle will be set to 0 when padAngle * nodeCount >= PI * 2 instead of decreasing the padAngle until it fits.

[Ovilia]

@pissang Thanks for the review!

Curious about the decision that padAngle will be set to 0 when padAngle * nodeCount >= PI * 2 instead of decreasing the padAngle until it fits.

How do you define until it fits? For example, if padAngle is 60 degrees and nodeCount is 10, do you mean padAngle should be 360 / 10 = 36 degree? If so, then all space is used for padAngle and shows no sector at all, which I don't think should be intuitive.

[pissang]

I'm thinking of constraints similar to the rules in flexbox, but I'm not sure yet what exactly those rules would be.

The main issue is that the overflow transition should be smooth, not just snap back to zero. That way, users won’t feel that jarring jump when crossing the threshold. As for what you mentioned about showing no sector at all — I assume that currently, at the exact threshold point(padAngle * nodeCount == PI * 2), it is also fully hidden?

[Ovilia]

@pissang I agree about using transition should be great if appliable.

Currently, at the exact threshold point(padAngle * nodeCount == PI * 2), padAngle would be 0 and sectors will have angles linear mapping to their values.

[echarts-bot]

Congratulations! Your PR has been merged. Thanks for your contribution! 👍