Desynchronisation between the mouse and the plot when scrolling

When we calculate the plot position, we use the cursor position on the whole page and not on the client!

We should use "ev.clientY"

Like that :

//these are some utility functions
getMousePosition(ev) {
var rect = this.svgEl.getBoundingClientRect();
if (ev.clientX && ev.clientY) return { x: ev.clientX - rect.left, y: ev.clientY - rect.top };
if (ev.targetTouches.length) return { x: ev.targetTouches[0].clientX - rect.left, y: ev.targetTouches[0].clientY - rect.top };
return { x: 0, y: 0 }; //oops?
}