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/**
* Drag.js: drag absolutely positioned HTML elements.
*
* This module defines a single drag( ) function that is designed to be called
* from an onmousedown event handler. Subsequent mousemove events will
* move the specified element. A mouseup event will terminate the drag.
* If the element is dragged off the screen, the window does not scroll.
* This implementation works with both the DOM Level 2 event model and the
* IE event model.
*
* Arguments:
*
* elementToDrag: the element that received the mousedown event or
* some containing element. It must be absolutely positioned. Its
* style.left and style.top values will be changed based on the user's
* drag.
*
* event: the Event object for the mousedown event.
**/
function drag(elementToDrag, event) {
// The mouse position (in window coordinates)
// at which the drag begins
var startX = event.clientX, startY = event.clientY;
// The original position (in document coordinates) of the
// element that is going to be dragged. Since elementToDrag is
// absolutely positioned, we assume that its offsetParent is the
// document body.
var origX = elementToDrag.offsetLeft, origY = elementToDrag.offsetTop;
// Even though the coordinates are computed in different
// coordinate systems, we can still compute the difference between them
// and use it in the moveHandler( ) function. This works because
// the scrollbar position never changes during the drag.
var deltaX = startX - origX, deltaY = startY - origY;
// Register the event handlers that will respond to the mousemove events
// and the mouseup event that follow this mousedown event.
if (document.addEventListener) { // DOM Level 2 event model
// Register capturing event handlers
document.addEventListener("mousemove", moveHandler, true);
document.addEventListener("mouseup", upHandler, true);
}
else if (document.attachEvent) { // IE 5+ Event Model
// In the IE event model, we capture events by calling
// setCapture( ) on the element to capture them.
elementToDrag.setCapture( );
elementToDrag.attachEvent("onmousemove", moveHandler);
elementToDrag.attachEvent("onmouseup", upHandler);
// Treat loss of mouse capture as a mouseup event.
elementToDrag.attachEvent("onlosecapture", upHandler);
}
else { // IE 4 Event Model
// In IE 4 we can't use attachEvent( ) or setCapture( ), so we set
// event handlers directly on the document object and hope that the
// mouse events we need will bubble up.
var oldmovehandler = document.onmousemove; // used by upHandler( )
var olduphandler = document.onmouseup;
document.onmousemove = moveHandler;
document.onmouseup = upHandler;
}
// We've handled this event. Don't let anybody else see it.
if (event.stopPropagation) event.stopPropagation( ); // DOM Level 2
else event.cancelBubble = true; // IE
// Now prevent any default action.
if (event.preventDefault) event.preventDefault( ); // DOM Level 2
else event.returnValue = false; // IE
/**
* This is the handler that captures mousemove events when an element
* is being dragged. It is responsible for moving the element.
**/
function moveHandler(e) {
if (!e) e = window.event; // IE Event Model
// Move the element to the current mouse position, adjusted as
// necessary by the offset of the initial mouse-click.
elementToDrag.style.left = (e.clientX - deltaX) + "px";
elementToDrag.style.top = (e.clientY - deltaY) + "px";
// And don't let anyone else see this event.
if (e.stopPropagation) e.stopPropagation( ); // DOM Level 2
else e.cancelBubble = true; // IE
}
/**
* This is the handler that captures the final mouseup event that
* occurs at the end of a drag.
**/
function upHandler(e) {
if (!e) e = window.event; // IE Event Model
// Unregister the capturing event handlers.
if (document.removeEventListener) { // DOM event model
document.removeEventListener("mouseup", upHandler, true);
document.removeEventListener("mousemove", moveHandler, true);
}
else if (document.detachEvent) { // IE 5+ Event Model
elementToDrag.detachEvent("onlosecapture", upHandler);
elementToDrag.detachEvent("onmouseup", upHandler);
elementToDrag.detachEvent("onmousemove", moveHandler);
elementToDrag.releaseCapture( );
}
else { // IE 4 Event Model
// Restore the original handlers, if any
document.onmouseup = olduphandler;
document.onmousemove = oldmovehandler;
}
// And don't let the event propagate any further.
if (e.stopPropagation) e.stopPropagation( ); // DOM Level 2
else e.cancelBubble = true; // IE
}
}