jaz303/tipsy — pull request #142 by ENOTTY (2013-03-04 02:16:55+00:00)
Title: Set offset value dynamically by function call.

I needed this to position the tooltip based on some svg rectangles with different sizes, similar to how the title can be set dynamically.

In this example, I initially bound some data to some svg rects.

```javascript
$('rect.salary').tipsy({
gravity: 'se',
offset: function() {
var d = this.__data__;
var o = y(d.y0)-y(d.y1);
return -o/2;
},
title: function() {
var d = this.__data__;
return d.y1 - d.y0;
}
});
```