Ben Ben - 8 months ago 42
jQuery Question

Javascript drag/drop - Illustrator style 'smart guides'

I'm looking for a way to implement Adobe Illustrator style 'smart guides' when dragging/dropping in Javascript. I'm currently using jQuery UI's


containment: 'parent',
snap: '.other-objects',
snapTolerance: 5

This does 90% of what I want - I can drag
around within it's parent, and it will snap it's edges to
when it gets close enough.

What I want, however, is for a line of some kind (or a guide of some kind) to appear, if it's in line with the edge of another object, so I can snap stuff in a row without them being directly next to each other.

Does anybody know if this is possible, or how I'd go about doing it?


I started messing around with a jsFiddle. It's not perfect, but it should get you started.

The bulk of the logic is within jQuery UI's drag event handler:

function (event, ui) {

        // You'll want to debounce this function so that it doesn't run every mouse move (e.g. see Ben Alman's site @
        var debounceTime = 200; // milliseconds
        setTimeout(function () {

            // Loop through all 'other-object's and see if we're lined up
            $(".other-object").each(function (idx, other) {
                var $other = $(other);

                // Determine whether we're "close enough" to display the line
                var padding = 1;
                var closeToLeft = Math.abs($other.offset().left - ui.offset.left) < padding;
                var closeToTop = Math.abs($other.offset().top - < padding;
                // You can add closeToRight/closeToBottom, but you may need to do some calculation, e.g. right = left + width

                // If we're close, display a line, otherwise remove that same line
                // TODO: Find a better way of tagging which 'other-object' this line belongs to, using IDs or something more stable than the index of the jQuery each() function!
                var id = 'leftOther' + idx;
                if (closeToLeft) {
                    console.debug(idx, 'left');
                    $('.parent').not(':has(#' + id + ')').append('<div id="' + id + '" class="line vertical" style="left: ' + $other.offset().left + 'px;"/>');
                } else {
                    $('#' + id).remove();

                id = 'topOther' + idx;
                if (closeToTop) {
                    console.debug(idx, 'top');
                    $('.parent').not(':has(#' + id + ')').append('<div id="topOther' + idx + '" class="line horizontal" style="top: ' + $other.offset().top + 'px;"/>');
                } else {
                    $('#' + id).remove();
            }); // End of 'other-object' loop

        }, debounceTime); // End of setTimeout
    } // End of drag function

If I have some time later I'll come back and give it some more thought, but figured you'd appreciate a semi-answer so start you off for now =)