var percentages = offsetToPercentage(g, event.offsetX, event.offsetY);
var xPct = percentages[0];
var yPct = percentages[1];
zoom(g, percentage, xPct, yPct);
var percentages = offsetToPercentage(g, event.offsetX, event.offsetY);
var xPct = percentages[0];
var yPct = percentages[1];
zoom(g, percentage, xPct, yPct);