Jquery draggable with zoom problem

Question

I am working on a page in witch all its contents are scaled by using zoom. The problem is that when I drag something in the page the dragging item gets a bad position that seems relative to the zoom amount.

To solve this I tried to do some math on the position of the draggable component, but seems that even tho visually its corrected, the "true" position its not recalculated.

here is some code to explain better:

var zoom = Math.round((parseFloat($("body").css("zoom")) / 100)*10)/10;

var x = $(this).data('draggable').position;
$(this).data('draggable').position.left = Math.round(x.left/zoom);
$(this).data('draggable').position.top = Math.round(x.top/zoom);

Any help would be greatly appreciated

Answer 1

Took a lot of time and effort to fix this, but finally, I have a solution that works.

This solution works for both Firefox and IE. #canvas is the div that contains the draggable. Note that we have to make sure the elements stays inside the canvas manually.

This also works if if canvas has a different zoom level than the rest of the page.

var pointerX;
var pointerY;
$(c).draggable({
  start : function(evt, ui) {
    pointerY = (evt.pageY - $('#canvas').offset().top) / zoom - parseInt($(evt.target).css('top'));
    pointerX = (evt.pageX - $('#canvas').offset().left) / zoom - parseInt($(evt.target).css('left'));
  },
  drag : function(evt, ui) {
    var canvasTop = $('#canvas').offset().top;
    var canvasLeft = $('#canvas').offset().left;
    var canvasHeight = $('#canvas').height();
    var canvasWidth = $('#canvas').width();

    // Fix for zoom
    ui.position.top = Math.round((evt.pageY - canvasTop) / zoom - pointerY); 
    ui.position.left = Math.round((evt.pageX - canvasLeft) / zoom - pointerX); 

    // Check if element is outside canvas
    if (ui.position.left < 0) ui.position.left = 0;
    if (ui.position.left + $(this).width() > canvasWidth) ui.position.left = canvasWidth - $(this).width();  
    if (ui.position.top < 0) ui.position.top = 0;
    if (ui.position.top + $(this).height() > canvasHeight) ui.position.top = canvasHeight - $(this).height();  

    // Finally, make sure offset aligns with position
    ui.offset.top = Math.round(ui.position.top + canvasTop);
    ui.offset.left = Math.round(ui.position.left + canvasLeft);
  }
});

Answer 2

var zoom = $('#canvas').css('zoom');    
$('#dragme').draggable({
        drag: function(evt,ui)
        {
             var factor = (1 / zoom) -1);

             ui.position.top += Math.round((ui.position.top - ui.originalPosition.top) * factor);
             ui.position.left += Math.round((ui.position.left- ui.originalPosition.left) * factor);    
        }                 
    });