jQuery Drag/Resize with CSS Transform Scale

Question

I am applying a CSS transform (and the browser specific -webkit, -o etc):

transform: matrix(0.5 , 0 , 0, 0.5, 0 , 0);

to a div then using jQuery\'s draggable

Answer 1

Another approach would be to add a plugin that compensate for the transformation ( remember to add "transform : true" to the plugin initialization.

The ui.draggable need to be passed via a inverse matrix of the transformation in order to position the element in the un-transformed space which the browser later transform on display.

For "draggable" the following worked for me ( jqueryui 1.10 ) ( the matrix calculation I have taken from jquery.panzoom):

var Matrix = function(a, b, c, d, e, f, g, h, i) {
    if ($.type(a) === 'array') {
        this.elements = [
            +a[0], +a[2], +a[4],
            +a[1], +a[3], +a[5],
                0,     0,     1
        ];
    } else {
        this.elements = [
            a, b, c,
            d, e, f,
            g || 0, h || 0, i || 1
        ];
    }
};

Matrix.prototype = {
    /**
     * Multiply a 3x3 matrix by a similar matrix or a vector
     * @param {Matrix|Vector} matrix
     * @return {Matrix|Vector} Returns a vector if multiplying by a vector
     */
    x: function(matrix) {
        var isVector = matrix instanceof Vector;

        var a = this.elements,
            b = matrix.elements;

        if (isVector && b.length === 3) {
            // b is actually a vector
            return new Vector(
                a[0] * b[0] + a[1] * b[1] + a[2] * b[2],
                a[3] * b[0] + a[4] * b[1] + a[5] * b[2],
                a[6] * b[0] + a[7] * b[1] + a[8] * b[2]
            );
        } else if (b.length === a.length) {
            // b is a 3x3 matrix
            return new Matrix(
                a[0] * b[0] + a[1] * b[3] + a[2] * b[6],
                a[0] * b[1] + a[1] * b[4] + a[2] * b[7],
                a[0] * b[2] + a[1] * b[5] + a[2] * b[8],

                a[3] * b[0] + a[4] * b[3] + a[5] * b[6],
                a[3] * b[1] + a[4] * b[4] + a[5] * b[7],
                a[3] * b[2] + a[4] * b[5] + a[5] * b[8],

                a[6] * b[0] + a[7] * b[3] + a[8] * b[6],
                a[6] * b[1] + a[7] * b[4] + a[8] * b[7],
                a[6] * b[2] + a[7] * b[5] + a[8] * b[8]
            );
        }
        return false; // fail
    },
    /**
     * Generates an inverse of the current matrix
     * @returns {Matrix}
     */
    inverse: function() {
        var d = 1 / this.determinant(),
            a = this.elements;
        return new Matrix(
            d * ( a[8] * a[4] - a[7] * a[5]),
            d * (-(a[8] * a[1] - a[7] * a[2])),
            d * ( a[5] * a[1] - a[4] * a[2]),

            d * (-(a[8] * a[3] - a[6] * a[5])),
            d * ( a[8] * a[0] - a[6] * a[2]),
            d * (-(a[5] * a[0] - a[3] * a[2])),

            d * ( a[7] * a[3] - a[6] * a[4]),
            d * (-(a[7] * a[0] - a[6] * a[1])),
            d * ( a[4] * a[0] - a[3] * a[1])
        );
    },
    /**
     * Calculates the determinant of the current matrix
     * @returns {Number}
     */
    determinant: function() {
        var a = this.elements;
        return a[0] * (a[8] * a[4] - a[7] * a[5]) - a[3] * (a[8] * a[1] - a[7] * a[2]) + a[6] * (a[5] * a[1] - a[4] * a[2]);
    }
};

var Vector = function (x, y, z) {
    this.elements = [ x, y, z ];
};

/**
 * Get the element at zero-indexed index i
 * @param {Number} i
 */
Vector.prototype.e = Matrix.prototype.e = function(i) {

    if( this.elements[ i ] != undefined ){
        return this.elements[ i ];    
    }

    return this.elements;
};    

$.ui.plugin.add("draggable", "transform", {

    start: function( event, ui ) {

        if(!$(this).data('ui-draggable')){
            return false;
        }            

        var inst = $(this).data("ui-draggable");

        inst.matrix = new Matrix(function(matrix){

            var rmatrix = new RegExp(
                    '^matrix\\(' +
                    '(\\-?[\\d\\.e]+)' + '\\,?\\s*' +
                    '(\\-?[\\d\\.e]+)' + '\\,?\\s*' +
                    '(\\-?[\\d\\.e]+)' + '\\,?\\s*' +
                    '(\\-?[\\d\\.e]+)' + '\\,?\\s*' +
                    '(\\-?[\\d\\.e]+)' + '\\,?\\s*' +
                    '(\\-?[\\d\\.e]+)' + '\\)$'
            );                

            var matrix = rmatrix.exec( matrix );
            if (matrix) {
                matrix.shift();
            }
            return matrix || [ 1, 0, 0, 1, 0, 0 ];

        }([$(this).parents('[style*="transform"]').css('transform')]));            
    },
    drag: function( event, ui ) {

        if(!$(this).data('ui-draggable')){
            return false;
        }            

        var inst = $(this).data("ui-draggable");

        var t_pos = inst.matrix.inverse().x(new Vector(ui.position.left, ui.position.top, 0));

        ui.position.left = t_pos.e(0);
        ui.position.top = t_pos.e(1);                   

        if(inst.options.grid) {
            ui.position.left = ui.position.left - ui.position.left % inst.options.grid[0];
            ui.position.top  = ui.position.top - ui.position.top % inst.options.grid[1];                
        }

        if( inst.containment ){

            if( ui.position.left < inst.containment[0] ){
                ui.position.left = inst.containment[0];
            }

            if( ui.position.left > inst.containment[2] ){
                ui.position.left = inst.containment[2];
            }                

            if( ui.position.top < inst.containment[1] ){
                ui.position.top = inst.containment[1];
            }  

            if( ui.position.top > inst.containment[3] ){
                ui.position.top = inst.containment[3];
            }
        }
    },     
});