Methods overwrite current transformation

[sergi]

Let's say I have the following code:

var el = draw.group();
el.attr('transform', 'matrix(1,0,0,-1,0,0)');

The node of this object has now the attribute transform="matrix(1,0,0,-1,0,0)".
If I now try move the element:

el.move(100, 0);

It resets all previous transformations, and its node transform attribute looks like transform="translate(0,100)".

Is that expected? Right now the only way to wor around this behavior is doing something like this:

  el.scale(1, -1);
  var t = el.transform();
  t.x = t.x + 100;
  el.transform(t);

[wout]

Yes this is expected. You should use the transfrom() method instead:

el.transform('matrix', '1,0,0,-1,0,0')

Transform values are numerically stored in order to be able to animate them. Or rather, not having to parse them over and over again. That is why all transformation should be applied through the transform() method.

The example above can also be achieved like this:

el.transform({ d: -1 })

As in matrix(a,b,c,d,e,f).

[sergi]

Right. So if I want to apply a scaleY of -1 and then later move the element 100px to the right I should to something like:

el.transform({ d: -1 });
//Other stuff happens, time passes
el.transform({ e: el.transform().x + 100 });

(e meaning the x component of the matrix, I assume that it could also be x instead of e). Please correct me if I'm wrong.

[wout]

Well, not exactly. Translations and matrices are applied separately. In other words, transformations are not combined into a matrix. If you move an element with:

rect.transform({ x: 100, y: 50 })

The value of the transform attribute will be translate(100,50).

If you add a matrix transformation afterwards, let's say:

rect.transform({ d: -1 })

The value of the transform attribute will be translate(100,50) matrix(1,0,0,-1,0,0).

Transformations are combined in svg. Recalculating transformations into a singular matrix would remove that.

To be honest, I have been thinking about going that way (one matrix to rule them all). But I decided to stay as close as possible to SVG's native behaviour.

[wout]

Are you with me on this?

[sergi]

Yeah. Perhaps adding extra utility methods that translate, scale, etc.
using matrix transformations is not a bad idea though (I am doing all with
matrix operations now). You could prefix them and keep the svg-standard
methods for users that prefer 1:1 mapping with the generated svg .

On the other hand, I would always expect that svg.js takes the most
performing path, regardless of the methods I use. For example, if I do
obj.x = 10 I would expect that a matrix transformation is applied behind
the scenes, if that's more performing.

On Friday, May 24, 2013, Wout Fierens wrote:

Are you with me on this?

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/38#issuecomment-18420057
.