How to set the Origin (drag.origin) for drag behavior in d3 JavaScript library

Question

I am trying to implement drag behavior for group consisting from HTML-text and background-rectangle using the d3 framework. I was able to get it working, although when not setting the drag.origin I can see noticeable jump due to the mouse-position/element-coordinates offset. Exactly how described on the d3 wiki-page Although the page described how to set the Origin for dragging, I do not properly understand how ti implement it in my example. I tried two different approaches : using the element for grouping the elements together and defining new element holding tose. In the first case I have to use the translate-function and I do not even know how to get the coordinates of the group.

var svg = d3.select("body").append("svg")
  .attr("width", 960)
  .attr("height", 500);

var group = svg.append("svg:g")
  .attr("transform", "translate(10, 10)")
  .attr("id", "group");

var rect1 = group.append("svg:rect")
  .attr("rx", 6)
  .attr("ry", 6)
  .attr("x", 5/2)
  .attr("y", 5/2)
  .attr("id", "rect")
  .attr("width", 250)
  .attr("height", 125)
  .style("fill", 'white')
  .style("stroke", d3.scale.category20c())
  .style('stroke-width', 5);


var html1 = group.append("foreignObject")
  .attr("x", 50)
  .attr("y", 25)
  .attr("width", 200)
  .attr("height", 100)
  .attr("id", "fobject")
  .style("border-color", d3.scale.category20c())
  .append("xhtml:div")
  .style("font", "14px 'Helvetica Neue'")
  .html("Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec eu enim quam.");

var innerSvg = svg.append("svg")
  .attr("x", 500)
  .attr("y", 10)
  .attr("id", "innerSvg");

var rect2 = innerSvg.append("svg:rect")
  .attr("rx", 6)
  .attr("ry", 6)
  .attr("x", 5/2)
  .attr("y", 5/2)
  .attr("id", "rect")
  .attr("width", 250)
  .attr("height", 125)
  .style("fill", 'white')
  .style("stroke", d3.scale.category20c())
  .style('stroke-width', 5);

var html2 = innerSvg.append("foreignObject")
  .attr("x", 50)
  .attr("y", 25)
  .attr("width", 200)
  .attr("height", 100)
  .attr("id", "fobject")
  .style("border-color", d3.scale.category20c())
  .append("xhtml:div")
  .style("font", "14px 'Helvetica Neue'")
  .html("Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec eu enim quam.");

var drag1 = d3.behavior.drag()
    .on("drag", function(d,i) {
        d3.select(this).attr("transform", function(d,i){
            return "translate(" + [ d3.event.x,d3.event.y ] + ")"
        })
    });

var drag2 = d3.behavior.drag()
    .on("drag", function(d,i) {
        d3.select(this)
        .attr("x", d3.event.x)
        .attr("y", d3.event.y);
    });

group.call(drag1);
innerSvg.call(drag2);

I would very appreciate any explanation, naturally I prepared a working example here : http://jsfiddle.net/Y8y7V/

Answer 1

You simply need to set the origin() function accordingly. In the second case this is straightforward, in the first case somewhat more difficult because you are using coordinates as well as a transform. The basic pattern (for the second case) looks like this:

 .origin(function() { 
        var t = d3.select(this);
        return {x: t.attr("x"), y: t.attr("y")};
    })

Updated jsfiddle here.

Answer 2

group element has no x/y attributes - no problem! create ones:

var node = svg.append("g")
            .attr('x',x_1)
            .attr('y',y_1)
            .attr("class","node")
            .attr("name","Node_A")
            .attr("transform","translate(" + x_1 + ", " + y_1 +")")
            .call(drag);

when, the .origin function from Lars will work

and dont forget to update x,y attributes, while dragging:

function dragged() {

    d3.select(this).attr("transform","translate(" + d3.event.x + ", " + d3.event.y +")");
    d3.select(this).attr("x",d3.event.x);
    d3.select(this).attr("y",d3.event.y);
}