raphaeljs: drag and apply transformation to Paper.set() - raphael

Question

I started to play a little bit with raphaeljs, however I'm having a small problem when dragging and applying a transformation to a Paper.set()
Here is my example: http://jsfiddle.net/PQZmp/2/
1) Why is the drag event added only to the marker and not the slider?
2) The transformation is supposed to be relative(i.e. translate by and not translate to), however if I drag the marker twice, the second dragging starts from the beginning and not from the end of the first.
EDIT:
After the response of Zero, I created a new JSFiddle example: http://jsfiddle.net/9b9W3/1/
1) It would be cool if this referenced the set instead of the first element of the set. Can't this be done with dragger.apply(slider)? I tried it, but only works on the first execution of the method (perhaps inside Raphael it is already being done but to the first element inside the set instead of the set)
2) According to Raphael docs the transformation should be relative to the object position (i.e. translate by and not translate to). But it is not what is happening according to the jsfiddle above (check both markers drag events).
3) So 2) above creates a third question. If a transform("t30,0") is a translation by 30px horizontally, how is the origin calculated? Based on attr("x") or getBBox().x?

Answer 1

The drag event is actually being added to both the marker and the slider -- but your slider has a stroke-width of 1 and no fill, so unless you catch the exact border, the click "falls through" to the canvas.
Behind that is another issue: the drag is being applied to both elements, but this in your drag handler references a specific element, not the set -- so both elements will drag independently from each other.
Lastly: the reason that each drag is starting from the initial position is because the dx, dy parameters in dragger are relative to the coordinates of the initial drag event, and your transform does not take previous transforms into account. Consider an alternative like this:
var r = new Raphael(0, 0, 400, 200);
var marker = r.path("M10,0L10,100").attr({"stroke-width": 5});
var button = r.rect(0, 0, 20, 20, 1).attr( { 'stroke-width': 2, fill: 'white' } );
var slider = r.set( marker, button );
var startx, starty;
var startDrag = function(){
var bbox = slider.getBBox();
startx = bbox.x;
starty = bbox.y;
console.log(this);
}, dragger = function(dx, dy){
slider.transform("t" + ( startx + dx ) + "," + starty );
}, endDrag = function(){
};
slider.drag(dragger, startDrag, endDrag);
To address your updates:
I believe you can specify the context in which the drag function will be executed as optional fourth, fifth, and six parameters to element.drag. I haven't tried this myself, but it looks like this should work great:
slider.drag( dragger, startDrag, endDrag, slider, slider, slider );
The transformation is relative to the object position. This works great for the first slider because its starting position is 0, but not so great for the second slider because...
...the transformation for min/max sliders should actually be relative to the scale, not the individual markers. Thus you will notice that your max slider (the red one) returns to its initial position just as you drag the mouse cursor back over the zero position. Make sense?

Answer 2

var position;
var rect = paper.rect(20, 20, 40, 40).attr({
cursor: "move",
fill: "#f00",
stroke: "#000"
});
t = paper.text(70,70, 'test').attr({
"font-size":16,
"font-family":
"Arial, Helvetica, sans-serif"
});
var st = paper.set();
st.push(rect, t);
rect.mySet = st;
rect.drag(onMove, onStart, onEnd);
onStart = function () {
positions = new Array();
this.mySet.forEach(function(e) {
var ox = e.attr("x");
var oy = e.attr("y");
positions.push([e, ox, oy]);
});
}
onMove = function (dx, dy) {
for (var i = 0; i < positions.length; i++) {//you can use foreach but I want to
// show that is a simple array
positions[i][0].attr({x: positions[i][1] + dx, y: positions[i][2] + dy});
}
}
onEnd = function() {}