How to set transform origin in SVG

Question

I need to resize and rotate certain elements in SVG document using javascript. The problem is, by default, it always applies the transform around the origin at (0, 0) – top left.

How can I re-define this transform anchor point?

I tried using the transform-origin attribute, but it does not affect anything.

This is how I did it:

svg.getDocumentById('someId').setAttribute('transform-origin', '75 240');

It does not seem to set the pivotal point to the point I specified although I can see in Firefox that the attribute is correctly set. I tried things like center bottom and 50% 100% with and without parenthesis. Nothing worked so far.

Can anyone help?

Answer 1

If you can use a fixed value (not "center" or "50%"), you can use CSS instead:

-moz-transform-origin: 25px 25px;
-ms-transform-origin:  25px 25px;
-o-transform-origin: 25px 25px;
-webkit-transform-origin:  25px 25px;
transform-origin: 25px 25px;

Some browsers (like Firefox) won't handle relative values correctly.

Answer 2

To rotate use transform="rotate(deg, cx, cy)", where deg is the degree you want to rotate and (cx, cy) define the centre of rotation.

For scaling/resizing, you have to translate by (-cx, -cy), then scale and then translate back to (cx, cy). You can do this with a matrix transform:

transform="matrix(sx, 0, 0, sy, cx-sx*cx, cy-sy*cy)"

Where sx is the scaling factor in the x-axis, sy in the y-axis.

Answer 3

For scaling without having to use the matrix transformation:

transform="translate(cx, cy) scale(sx sy) translate(-cx, -cy)"

And here it is in CSS:

transform: translate(cxpx, cypx) scale(sx, sy) translate(-cxpx, -cypx)

Answer 4

I had a similar issue. But I was using D3 to position my elements, and wanted the transform and transition to be handled by CSS. This was my original code, which I got working in Chrome 65:

//...
this.layerGroups.selectAll('.dot')
  .data(data)
  .enter()
  .append('circle')
  .attr('transform-origin', (d,i)=> `${valueScale(d.value) * Math.sin( sliceSize * i)} 
                                     ${valueScale(d.value) * Math.cos( sliceSize * i + Math.PI)}`)
//... etc (set the cx, cy and r below) ...

This allowed me to set the cx,cy, and transform-origin values in javascript using the same data.

BUT this didn't work in Firefox! What I had to do was wrap the circle in the g tag and translate it using the same positioning formula from above. I then appended the circle in the g tag, and set its cx and cy values to 0. From there, transform: scale(2) would scale from the center as expected. The final code looked like this.

this.layerGroups.selectAll('.dot')
  .data(data)
  .enter()
  .append('g')
  .attrs({
    class: d => `dot ${d.metric}`,
    transform: (d,i) => `translate(${valueScale(d.value) * Math.sin( sliceSize * i)} ${valueScale(d.value) * Math.cos( sliceSize * i + Math.PI)})`
  })
  .append('circle')
  .attrs({
    r: this.opts.dotRadius,
    cx: 0,
    cy: 0,
  })

After making this change, I changed my CSS to target the circle instead of the .dot, to add the transform: scale(2). I didn't even need use transform-origin.

NOTES:

1. I am using d3-selection-multi in the second example. This allows me to pass an object to .attrs instead of repeating .attr for every attribute.

2. When using a string template literal, be aware of line-breaks as illustrated in the first example. This will include a newline in the output and may break your code.

Answer 5

If you're like me and want to pan and then zoom with transform-origin, you'll need a little more.

// <g id="view"></g>
var view = document.getElementById("view");

var state = {
  x: 0,
  y: 0,
  scale: 1
};

// Origin of transform, set to mouse position or pinch center
var oX = window.innerWidth/2;
var oY = window.innerHeight/2;

var changeScale = function (scale) {
  // Limit the scale here if you want
  // Zoom and pan transform-origin equivalent
  var scaleD = scale / state.scale;
  var currentX = state.x;
  var currentY = state.y;
  // The magic
  var x = scaleD * (currentX - oX) + oX;
  var y = scaleD * (currentY - oY) + oY;

  state.scale = scale;
  state.x = x;
  state.y = y;

  var transform = "matrix("+scale+",0,0,"+scale+","+x+","+y+")";
  //var transform = "translate("+x+","+y+") scale("+scale+")"; //same
  view.setAttributeNS(null, "transform", transform);
};

Here it is working: http://forresto.github.io/dataflow-prototyping/react/