Mochikit Drag&Drop Corner Case

I found myself working again on the UI for my startup. As my Javascript library, I use Mochikit. One of the reasons for that is that it’s the Turbogears builtin, and I came to like it. The other is that it’s really easy to create DOM objects with it.

In any case, Mochikit has really easy support for good looking drag&drop. However, as usual, my requirements were strange enough to fall upon the following corner case:
I wanted to add a “tool tip popup” for some text, where I would display pertinent information to said text. To make the tool tip popup thingy work, I used the following css “on mouse over” visibility trick:
.tooltip {
display: none;

.parent_object_class:hover .tooltip {
display: block;

This works beautifully, and with a little bit of positioning, and maybe an event here and there, you can make it appear where you want.

Cue the drag&drop. I wanted to add some drag&drop based slider to that tool tip. Since I wanted to limit the “draggability” of the slider’s selector, I used the snap argument for Mochikit’s Draggable object so that if you move the mouse too far, the dragged selector stays at the limit of a predefined area.
This was all very well, and both of the tricks described worked pretty fine separately, until I tried to put them together.
When dragging and leaving the allowed area for the drag, because of the snap argument, the dragged object stays back, and mouse is no longer over a child element of the original tooltip and tooltipped text. This means that the css trick no longer applies, and the tooltip loses visibility. This would have been fine if the drag ended there. However, the drag was not ended, and at each move of the mouse, the coordinates would grow more. Since I use the drag coordinates to compute the result of the drag, I got some pretty strange results.

To work around this behavior, I used Draggable’s starteffect and endeffect optional arguments to make sure the tooltip remained visible, thus avoiding this issue.

Still, there were many other issues with all this drag&drop going around, and I decided to go for a simpler design, and not put in more time on this.
Issue sealed with a Keep It Simple Stupid.

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