I am currently building a widget that will allow users to design a layout for an application-specific task. And I would like to provide a powerpoint/keynote-esque interface (a la 280slides) for the users. However, I would also like to provide "snap guides" (sorry, I do not have any better words to describe them) which are basically guides taht help users align multiple elements on the page.
An example of this can be seen in the Flash IDE where, upon dragging the IDE automatically calculates the dimension and position of peripheral objects and attempts to align them. The mockingbird application (https://gomockingbird.com/mockingbird/) achieves something similar. (Hint: try dragging some objects and see how there are guides which attempt to align the object in their bounding boxes).
I believe a similar effect could be achived by caching an array of elements on the viewport and calculating the position and dimension of each element to find the best-fit snap. However, how do I calculate the most-probable position of the element being dragged? Are there any alternative solutions?
With someone with better knowledge, please enlighten me! :)
I suggest using a library that has already been written to accomplish this. For example, jQuery UI's Draggable does exactly this and is very customizable.