activate tooltips on hover anywhere on the map

[titaniumbones]

c3.js and its fork billboard.js have tooltips that activate no matter where you hover on the map. They do this, I believe, by calculating x-distance from the mouse to the relevant points.

I would love to be able to do something similar in chartist. Since this plugin uses the mouseover event, this may be somewhat difficult to achieve without a substantial rewrite, but I would be grateful for your opinion.

This would also help to address https://github.com/tmmdata/chartist-plugin-tooltip/issues/157, insofar as both feature requests try to address a usability problem in which it's difficult to maintain mouse focus on the tiny elements that cause hte tooltip to appear.

[lukbukkit]

That's sounds like a good idea, but unfortunately I currently don't have the time to implement this feature like this. If you've got some time, a pull request is welcome, otherwise I'll try to work on this during my christmas holidays.