How are the curves in the Echarts relationship table made?

I"d like to ask about this picture in the official case of Echarts:

clipboard.png

how the curve between two nodes is made. There should be an "invisible limit point", and it feels that the coordinate of this point should be the angle is the middle value of the angle of the two connected nodes (calculated by inferior arc), but how is the polar coordinate radius of this restriction point determined? Is there any way to calculate? no, no, no. Ask ~

Feb.25,2022

should be Bezier curve, svg, not sure

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