Add an event to the droppable system.

I needed to implement a somewhat complex intersection logic. The drop zone elements were hidden until active (display:none), only one could be active at a time, etc. etc.

Rather than trying to accommodate a bunch of odd droppable situations like mine, what if an event were added during the intersect function. That way intersection logic could be applied by the user for unusual circumstances.

Something like this:

// Get the drop position.
var pos = { l : droppable.offset.left, r : l + droppable.item.proportions.width, 
            t : droppable.offset.top,  b : t + droppable.item.proportions.height };

// If a custom onposition function is defined, fire it.  If that function returns false, we will not activate this droppable.
if ($.isFunction(droppable.item.options.onposition) &&
    droppable.item.options.onposition.call(this,draggable,droppable,pos) == false)
{
    return false;
}

// Assign the droppable position.
var l = pos.l, r = pos.r, t = pos.t, b = pos.b;

The event is "onposition". If nothing were defined in the options, the calculations would go ahead as usual. If the onposition event were defined, the users's code could modify the droppable top/right/bottom/left as appropriate.

Optionally, if that event returned "false", this means that the drop zone cannot be activated even if it would otherwise intersect. I used this to only allow one active drop zone at a time, even if the draggable intersected two drop zones simultaneously.

What do you think?

JK