Question

How can I make a palette behaviour (elements being dragged and dropped from a ‘palette’ to a ‘canvas’) in raphaelJS?

Answer 1

You’ll have to add to every palette element this startFunction:

//DragFunctions is the object that has all the 3 d&d methods, clearer in the complete file
paletteStart: function () {
    // keep the relative coords at the start of the drag
    this.ox = 0;
    this.oy = 0;

    // as we are dragging the palette element, we clone it to leave one in his place.
    var newPaletteObj = this.clone();

    //we give the new palette element the behaviour of a palette element
    DragFunctions.addDragAndDropCapabilityToPaletteOption(newPaletteObj);

    //nice animation
    this.animate({
        "opacity": 0.5
    }, 500);
}

Now we need the function while the element is being dragged:

move: function (dx, dy) {
    // calculate translation coords
    var new_x = dx - this.ox;
    var new_y = dy - this.oy;

    // transforming coordinates
    this.transform('...T' + new_x + ',' + new_y);

    // save the new values for future drags
    this.ox = dx;
    this.oy = dy;
}

And finally, the function executed at finish dropping:

paletteUp: function () {
    if (!DragFunctions.isInsideCanvas(this)) {
        this.remove();
        //notify the user as you want!
    } else {
        //Giving the new D&D behaviour
        this.undrag();
        //give the element the new d&d functionality!
        this.animate({
            "opacity": 1
        }, 500);
    }
}

2 things to comment here, when the element is dropped, you will have to remove the palette behaviour and give it another one (a plain d&d functionality), if not, it will continue cloning elements all around.
Here I give you some nice behaviour to give them:

start: function () {
    // keep the relative coords at the start of the drag
    this.ox = 0;
    this.oy = 0;
    // animate attributes to a "being dragged" state
    this.animate({
        "opacity": 0.5
    }, 500);
},
//same move function
up: function () {
    if (!DragFunctions.isInsideCanvas(this)) {
        this.animate({
            transform: '...T' + (-this.ox) + ',' + (-this.oy)
        }, 1000, "bounce");
    }
    this.animate({
        "opacity": 1
    }, 500);
},

//and the method that gives the behaviour
addDragAndDropCapabilityToSet: function (compSet) {
    compSet.drag(this.move, this.start, this.up, compSet, compSet, compSet);
}

And as you may also see, we have a validator that sees if the element is inside the canvas, it is a very useful function, here:

isInsideCanvas: function (obj) {
    var canvasBBox = //get your 'canvas'
    var objectBBox = obj.getBBox();
    var objectPartiallyOutside = !Raphael.isPointInsideBBox(canvasBBox, objectBBox.x, objectBBox.y) || !Raphael.isPointInsideBBox(canvasBBox, objectBBox.x, objectBBox.y2) || !Raphael.isPointInsideBBox(canvasBBox, objectBBox.x2, objectBBox.y) || !Raphael.isPointInsideBBox(canvasBBox, objectBBox.x2, objectBBox.y2);
    return !(objectPartiallyOutside);
} Finally,
the place to call to give the element all this behaviour:

//this works for elements and sets
addDragAndDropCapabilityToPaletteOption: function (compSet) {
    compSet.drag(this.move, this.paletteStart, this.paletteUp, compSet, compSet, compSet);
}

A demo of this is in a website I created to play with raphael, called comoformamos.com
The hole code is in a github gist or hosted on github so if you want to get a little deeper in the code feel free to do it.

Explained more beautifully at this blog entry: devhike, I’m the author.