.drag { position: relative; }
var _startX = 0; // mouse starting positions
var _startY = 0;
var _offsetX = 0; // current element offset
var _offsetY = 0;
var _dragElement; // needs to be passed from OnMouseDown to OnMouseMove
var _oldZIndex = 0; // we temporarily increase the z-index during drag
var _debug = $('debug'); // makes life easier
InitDragDrop();
function InitDragDrop()
{
document.onmousedown = OnMouseDown;
document.onmouseup = OnMouseUp;
}
function OnMouseDown(e)
{
// IE is retarded and doesn't pass the event object
if (e == null)
e = window.event;
// IE uses srcElement, others use target
var target = e.target != null ? e.target : e.srcElement;
_debug.innerHTML = target.className == 'drag'
? 'draggable element clicked'
: 'NON-draggable element clicked';
// for IE, left click == 1
// for Firefox, left click == 0
if ((e.button == 1 && window.event != null ||
e.button == 0) &&
target.className == 'drag')
{
// grab the mouse position
_startX = e.clientX;
_startY = e.clientY;
// grab the clicked element's position
_offsetX = ExtractNumber(target.style.left);
_offsetY = ExtractNumber(target.style.top);
// bring the clicked element to the front while it is being dragged
_oldZIndex = target.style.zIndex;
target.style.zIndex = 10000;
// we need to access the element in OnMouseMove
_dragElement = target;
// tell our code to start moving the element with the mouse
document.onmousemove = OnMouseMove;
// cancel out any text selections
document.body.focus();
// prevent text selection in IE
document.onselectstart = function () { return false; };
// prevent IE from trying to drag an image
target.ondragstart = function() { return false; };
// prevent text selection (except IE)
return false;
}
}
function OnMouseMove(e)
{
if (e == null)
var e = window.event;
// this is the actual "drag code"
_dragElement.style.left = (_offsetX + e.clientX - _startX) + 'px';
_dragElement.style.top = (_offsetY + e.clientY - _startY) + 'px';
_debug.innerHTML = '(' + _dragElement.style.left + ', ' +
_dragElement.style.top + ')';
}
function OnMouseUp(e)
{
if (_dragElement != null)
{
_dragElement.style.zIndex = _oldZIndex;
// we're done with these events until the next OnMouseDown
document.onmousemove = null;
document.onselectstart = null;
_dragElement.ondragstart = null;
// this is how we know we're not dragging
_dragElement = null;
_debug.innerHTML = 'mouse up';
}
}
function ExtractNumber(value)
{
var n = parseInt(value);
return n == null || isNaN(n) ? 0 : n;
}
// this is simply a shortcut for the eyes and fingers
function $(id)
{
return document.getElementById(id);
}
