Parse SVG transform attribute with javascript

Question

Supposing we have an SVG transform string:

transform = "translate(6,5),scale(3,3)";

Is there a slick regex function we could use to parse that into something usable?

Answer 1

Here's a nifty little snippet of code that might get you what you need, it should cover most scenario in case the string you intend to parse has different number of arguments:

function parse (a)
{
    var b={};
    for (var i in a = a.match(/(\w+\((\-?\d+\.?\d*e?\-?\d*,?)+\))+/g))
    {
        var c = a[i].match(/[\w\.\-]+/g);
        b[c.shift()] = c;
    }
    return b;
}

Running this

parse('translate(6,5),scale(3,3.5),a(1,1),b(2,23,-34),c(300)');

Will result in this:

{
    translate: [ '6', '5' ],
    scale: [ '3', '3.5' ],
    a: [ '1', '1' ],
    b: [ '2', '23', '-34' ],
    c: [ '300' ]
}

Answer 2

Assuming you are running in a browser, you could also use the SVG DOM to parse and decode the transform string.

var svgns = "http://www.w3.org/2000/svg";

function getTransformList(transformStr)
{
  // Create a fake <rect> element to set the transform to
  var rect = document.createElementNS(svgns, "rect");
  rect.setAttribute("transform", transformStr);
  // Use the DOM to get the list of decoded transforms
  dumpTransform(rect.transform.baseVal);
}

function dumpTransform(transformList)
{
  for (var i = 0; i < transformList.numberOfItems; i++)
  {
    var transform = transformList.getItem(i);
    var m = transform.matrix;
    switch (transform.type)
    {
      case 2:
        console.log("translate("+m.e+","+m.f+")");
        break;
      case 3:
        console.log("scale("+m.a+","+m.d+")");
        break;
      case 4:
        console.log("rotate("+transform.angle+")");
        // TODO need to also handle rotate(angle, x, y) form
        break;
      case 5:
        // TODO skewX()
        break;
      case 6:
        // TODO skewY(()
        break;
      case 1:
      default:
        console.log("matrix("+m.a+","+m.b+","+m.c+","+m.d+","+m.e+","+m.f+")");
        break;
    }
  }
}

getTransformList("translate(6,5),scale(3,3)");

Answer 3

Adapted from @chernjie's solution:

function parse_transform(a) {
    var b = {};
    for (var i in a = a.match(/(\w+)\(([^,)]+),?([^)]+)?\)/gi)) {
        var c = a[i].match(/[\w\.\-]+/g);
        b[c.shift()] = c;
    }
    return b;
}

Answer 4

var transform = "translate(6,5),scale(3,3)";
var translate  = /translate\(\s*([^\s,)]+)[ ,]([^\s,)]+)/.exec(transform);
var translateX = translate[1]
var translateY = translate[2]
var scale  = /scale\(\s*([^\s,)]+)[ ,]([^\s,)]+)/.exec(transform);
var scaleX = translate[1]
var scaleY = translate[2]

transformValues = {translate:{x:translateX,y:translateY},
scale:{x:scaleX,y:scaleY}}

Pretty gross, but @icedwater was making me do all the work myself so...

Answer 5

I'll take a stab at this and say you want it to be parsed into a JSON object containing each of the properties as an entry in a list. This is the closest I have come so far:

function listIntoJSON(theTransformInQuestion) {

    // let's work with transform = "translate(6,5),scale(3,3)" as specified.
    var result = [];  // empty list to be returned
    var splitList = theTransformInQuestion.split(/\W/);
    // now splitList is ["translate", "6", "5", "", "scale", "3", "3", ""]

    for (var t = 0; t < splitList.length; t += 4) {
        var op  = {};
        op.name = splitList[t];
        op.x    = splitList[t + 1];
        op.y    = splitList[t + 2];
        result.push(op);  // add op to the result list
    }
    return result;
}

which will take

transform = "translate(6,5),scale(3,3)";

and return

[
    {name: "translate", x: "6", y: "5"}, 
    {name: "scale", x: "3", y: "3"}
]

and should work for any number of transforms. Bit of a hack, but it will do for now.

Answer 6

even it's an old question, today I had the same need and ended up with this regex:

const regex = /((\w+)\((,?\s*-?\d*\.?\d+(px|in|px|cm|mm|pt|pc|em|ex|ch|rem|deg|rad|grad|turn)?)+\)\s*)/gi;

Quite long, but it takes into account unit of measure too.

You can test it here: https://regex101.com/r/M8rRjo/1/

Answer 7

It's not regex, but there is a similar question (Replacing d3.transform in D3 v4) with a very nice, comprehensive solution:

function getTransformation(transform) {
  // Create a dummy g for calculation purposes only. This will never
  // be appended to the DOM and will be discarded once this function 
  // returns.
  var g = document.createElementNS("http://www.w3.org/2000/svg", "g");
  
  // Set the transform attribute to the provided string value.
  g.setAttributeNS(null, "transform", transform);
  
  // consolidate the SVGTransformList containing all transformations
  // to a single SVGTransform of type SVG_TRANSFORM_MATRIX and get
  // its SVGMatrix. 
  var matrix = g.transform.baseVal.consolidate().matrix;
  
  // Below calculations are taken and adapted from the private function
  // transform/decompose.js of D3's module d3-interpolate.
  var {a, b, c, d, e, f} = matrix;   // ES6, if this doesn't work, use below assignment
  // var a=matrix.a, b=matrix.b, c=matrix.c, d=matrix.d, e=matrix.e, f=matrix.f; // ES5
  var scaleX, scaleY, skewX;
  if (scaleX = Math.sqrt(a * a + b * b)) a /= scaleX, b /= scaleX;
  if (skewX = a * c + b * d) c -= a * skewX, d -= b * skewX;
  if (scaleY = Math.sqrt(c * c + d * d)) c /= scaleY, d /= scaleY, skewX /= scaleY;
  if (a * d < b * c) a = -a, b = -b, skewX = -skewX, scaleX = -scaleX;
  return {
    translateX: e,
    translateY: f,
    rotate: Math.atan2(b, a) * 180 / Math.PI,
    skewX: Math.atan(skewX) * 180 / Math.PI,
    scaleX: scaleX,
    scaleY: scaleY
  };
}

console.log(getTransformation("translate(20,30)"));  
console.log(getTransformation("rotate(45) skewX(20) translate(20,30) translate(-5,40)"));