This pull request is in the type of:
- bug fixing
- new feature
- others
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
- This PR depends on ZRender changes (ecomfe/zrender#xxx).
N.A.
- Please squash the commits into a single one when merging.