Function getNaturalDragY

src/components/legend/draw.js:391–394

(scrollBoxY0, eventY0, eventY1)

                };

                var getNaturalDragY = function(scrollBoxY0, eventY0, eventY1) {
                    var y = ((eventY0 - eventY1) / scrollRatio) + scrollBoxY0;
                    return Lib.constrain(y, 0, scrollBoxYMax);
                };

                // scroll legend by dragging scrollBAR
                var scrollBarDrag = d3.behavior.drag()