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Re: Proposal: Nesting SVG Graphics Elements

From: Jeremie Patonnier <jeremie.patonnier@gmail.com>
Date: Mon, 3 Dec 2012 12:12:35 +0100
Message-ID: <CAEi838m-JLC0+bM6GTf8osBSt8cDbc5aG=wgq-kSjXKTbBy_XA@mail.gmail.com>
To: Doug Schepers <schepers@w3.org>
Cc: SVG public list <www-svg@w3.org>

I just come to add my author's 2ct to the discussion. Note that I just
express a very personal opinion here and I do not pretend to speak to
anybody else.

2012/11/29 Doug Schepers <schepers@w3.org>

> Hi, SVG WG-
> I have a proposal that may make SVG2 easier to understand and use for
> people already familiar with the HTML+CSS world.

> The basic idea is to allow rendering elements to also serve as container
> elements, with child rendering elements also rendered. (This is currently
> not very clearly specified in SVG1.1.)
> Currently, to associate 2 rendering elements, you have to use a group,
> like this:
>   <g id="g1">
>     <rect id="r1" x="5" y="10" width="70" height="40" fill="yellow"
> stroke="red" />
>     <text id="t1" x="15" y="35" font-size="12" fill="crimson">Some
> label</text>
>   </g>

> This can be problematic for positioning the elements relative to one
> other, and to moving the whole unit (yes, you can use a transform, but for
> drag-n-drop, you have to know what to grab and drag).

Yes, I think this is the main issue with SVG, elements are all positioned
relatively to the same point of origine. I egree this is something a bit
disruptive for people that come from the HTML+CSS world (where everything
is relative), but frankly, it doesn't require hours of work to understand
the basics.

> We could allow authors to do this by simply nesting the text element,
> which would render on top of the rect (using the same Painter's Model), and
> could be positioned relative to the new established coordinate space of the
> parent shape:
>   <rect id="r2" x="5" y="10" width="70" height="40" fill="yellow"
> stroke="red">
>     <text id="t2" x="50%" y="50%" font-size="12" fill="crimson">Some
> label</text>
>   </rect>

Hug! I'm not sure it's that simple because it leads to hundreds of
questions that were pointless before that. One of the biggest is related to
the inheritance of CSS properties. For example, in your code sample, does
the text inherit the stroke property from the rect? All of this is not
define and it's a huge work to check all of this for, IMO a very small

I agree with Tab that having to set a translation to a <g> element in order
to reposition a whole group sucks and is far from obvious.

But if the true issue is to have a way to position element in a relative
maner, I suggest another solution:

<g dx="10" dy="10">
  <rect x="10" y="10" width="50" height="50">

The dx and dy attribute on the g element could be use to shift the point of
origine used to position its children. So in the previous example, the
<rect> element is position at the coordinate 20,20 (dx+x , dy+y)

This allow to build some interested shift in nested elements

<g dx="10" dy="10">
  <g dx="5" dy="-5">
    <rect x="10" y="10" width="50" height="50">

Now, the <rect> element is at the coordinate 25,15

And it should be possible to even redefine a coordinate system related to
the root coordinate system with the x and y attribute applied on the <g>

<g dx="10" dy="10">
  <g dx="5" dy="-5">
    <g x="0" y="0">
      <rect x="10" y="10" width="50" height="50">

With x and y we offer authors a convenient way to reset the coordinate
system even if they have build an insane tree of <g> elements (end they
will). With that last example, the <rect> element is back a the coordinate

I really think that will make things a lot easier for people coming from
the HTML+CSS world: They have nothing to worry about the few thing they
already know about SVG and CSS, but they can build things in ways that make
position relative one against another.

This alternative proposal does not really change SVG as it is and offer a
nice short cut for user who wish to perform SVG hand editing.

Web : http://jeremie.patonnier.net
Twitter : @JeremiePat <http://twitter.com/JeremiePat>
Received on Monday, 3 December 2012 11:13:24 UTC

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