javascript - Isometric object detection

Question

I'm currently using this for collsion detection:

    var overlaps = (function () {
    function getPositions( elem ) {
        var pos, width, height;
        pos = $( elem ).position();
        width = $( elem ).width();
        height = $( elem ).height();
        return [ [ pos.left, pos.left + width ], [ pos.top, pos.top + height ] ];
    }

    function comparePositions( p1, p2 ) {
        var r1, r2;
        r1 = p1[0] < p2[0] ? p1 : p2;
        r2 = p1[0] < p2[0] ? p2 : p1;
        return r1[1] > r2[0] || r1[0] === r2[0];
    }

    return function ( a, b ) {
        var pos1 = getPositions( a ),
            pos2 = getPositions( b );
        return comparePositions( pos1[0], pos2[0] ) && comparePositions( pos1[1], pos2[1] );
    };

})();

But the problem is i work with isometric images for buildings, so there is a large empty area where you cannot place currently. For example:


So i cannot place them more closer to eachother.
How can i fix this,

My Image is loaded like this:

<div id='obj' name="build_6" class="build_88" style='top:584px;left:1094px;'><img src ="img/buildings/6.png" /></div>

Thank you,
Jeffrey

Answer 1

You probably need to use "real" overlap detection - as in, using a bounding box or a bounding circle/ellipsis, instead of comparing the element sizes.

A bounding circle is probably the easiest to implement in terms of algorithm complexity. For example, http://mathworld.wolfram.com/Circle-CircleIntersection.html