Fix(legend.scroll): scroll animation start position was incorrect

[susiwen8]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Fix legend scroll animation always start at first element, even the page number wasn't 1.
The problem was that legend content group always reset position to first element before animation.

Fixed issues

Details

Before: What was the problem?

After: How is it fixed in this PR?

Usage

Are there any API changes?

• The API has been changed.

Related test cases or examples to use the new APIs

NA.

Others

Merging options

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

Other information

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[susiwen8]

Clearly contentPos has some reason to be there, I look into it.

[pissang]

@100pah Can you explain the purpose of contentPos. Obviously, the current animation is not correct.

[100pah]

@pissang @susiwen8
This animation is correct in 4.9.
But there is a mistake when refactor it from position to xy in 5.0.

The reason of contentPos:
in case that the elements inside contentGroup are layout not based on [0, 0]. (for example, the left-top displayable part is at [-0.5, -0.5])
In most cases that will not happen.

[echarts-bot]

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