Get element -moz-transform:rotate value in jQuery

Question

I have CSS style for a layer:

.element {
    -webkit-transform: rotate(7.5deg);    
     -moz-transform: rotate(7.5deg);    
      -ms-transform: rotate(7.5deg);    
       -o-transform: rotate(7.5deg);   
          transform: rotate(7.5deg);
}

Is there a way to get curent rotation value through jQuery?

I tried this

$('.element').css("-moz-transform")

The result is matrix(0.991445, 0.130526, -0.130526, 0.991445, 0px, 0px) which doesn't tell me a lot. What I'm looking to get is 7.5.

Solution 1

Here's my solution using jQuery.

This returns a numerical value corresponding to the rotation applied to any HTML element.

function getRotationDegrees(obj) {
    var matrix = obj.css("-webkit-transform") ||
    obj.css("-moz-transform")    ||
    obj.css("-ms-transform")     ||
    obj.css("-o-transform")      ||
    obj.css("transform");
    if(matrix !== 'none') {
        var values = matrix.split('(')[1].split(')')[0].split(',');
        var a = values[0];
        var b = values[1];
        var angle = Math.round(Math.atan2(b, a) * (180/Math.PI));
    } else { var angle = 0; }
    return (angle < 0) ? angle + 360 : angle;
}

angle1 = getRotationDegrees($('#myDiv'));
angle2 = getRotationDegrees($('.mySpan a:last-child'));

etc...

Solution 2

I've found a bug/features in the Twist's code: the function return negative angles.

So I've add a simple line of code before returning the angle:

if(angle < 0) angle +=360;

Than the results will be:

function getRotationDegrees(obj) {
    var matrix = obj.css("-webkit-transform") ||
    obj.css("-moz-transform")    ||
    obj.css("-ms-transform")     ||
    obj.css("-o-transform")      ||
    obj.css("transform");
    if(matrix !== 'none') {
        var values = matrix.split('(')[1].split(')')[0].split(',');
        var a = values[0];
        var b = values[1];
        var angle = Math.round(Math.atan2(b, a) * (180/Math.PI));
    } else { var angle = 0; }

    if(angle < 0) angle +=360;
    return angle;
}

Solution 3

My Solution (using jQuery):

$.fn.rotationInfo = function() {
    var el = $(this),
        tr = el.css("-webkit-transform") || el.css("-moz-transform") || el.css("-ms-transform") || el.css("-o-transform") || '',
        info = {rad: 0, deg: 0};
    if (tr = tr.match('matrix\\((.*)\\)')) {
        tr = tr[1].split(',');
        if(typeof tr[0] != 'undefined' && typeof tr[1] != 'undefined') {
            info.rad = Math.atan2(tr[1], tr[0]);
            info.deg = parseFloat((info.rad * 180 / Math.PI).toFixed(1));
        }
    }
    return info;
};

Usage:

$(element).rotationInfo(); // {deg: 7.5, rad: 0.13089969389957515}
$(element).rotationInfo().deg; // 7.5

Solution 4

Here is a plug-in version of Twist's function. Also, the conditional if(matrix !== 'none') did not work for me. So I have added type-checking:

(function ($) {
    $.fn.rotationDegrees = function () {
         var matrix = this.css("-webkit-transform") ||
    this.css("-moz-transform")    ||
    this.css("-ms-transform")     ||
    this.css("-o-transform")      ||
    this.css("transform");
    if(typeof matrix === 'string' && matrix !== 'none') {
        var values = matrix.split('(')[1].split(')')[0].split(',');
        var a = values[0];
        var b = values[1];
        var angle = Math.round(Math.atan2(b, a) * (180/Math.PI));
    } else { var angle = 0; }
    return angle;
   };
}(jQuery));

Use as follows:

var rotation = $('img').rotationDegrees();

Solution 5

The CSS tranform property will always return a matrix value, as rotate, skew, scale etc. is just shorthand for doing things easier, and not having to calculate the matrix value everytime, however the matrix is calculated by the browser and applied as a matrix, and when that is done it can no longer return the rotated degree by angle without recalculating the matrix back again.

To make such calcualtions easier there is a javascript library called Sylvester that was created for the purpose of easy matrix calculation, try looking at that to get the rotation degree from the matrix value.

Also, if you where to write a rotate function in javascript to translate rotational degrees to a matrix, it would probably look something like this (this uses sylvester for the last calculation) :

var Transform = {
    rotate: function(deg) {
        var rad = parseFloat(deg) * (Math.PI/180),
            cos_theta = Math.cos(rad),
            sin_theta = Math.sin(rad);

        var a = cos_theta,
            b = sin_theta,
            c = -sin_theta,
            d = cos_theta;

        return $M([
          [a, c, 0],
          [b, d, 0],
          [0, 0, 1]
        ]);
    }
};

Now all you really have to do is reverse enginer that function and you're golden :-)

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