RE: SVG 1.1 Spec Rec - 7.6 The Transform Attribute

Patrick,
Transformations can get confusing if you attempt to explain them in 
simplistic term. Regarding your question, the SVG 1.1 specification is 
fairly clear about this in 
http://www.w3.org/TR/SVG11/coords.html#TransformAttribute. It says:

    <rect x="10" y="10" width="20" height="20" transform="scale(2)"/>

is equivalent to:

    <g transform="scale(2)">
      <rect x="10" y="10" width="20" height="20"/>
    </g>

and then that:

   <g transform="translate(-10,-20) scale(2) rotate(45) translate(5,10)">
     <!-- graphics elements go here -->
   </g>

is equivalent to:

   <g transform="translate(-10,-20)">
     <g transform="scale(2)">
       <g transform="rotate(45)">
         <g transform="translate(5,10)">
           <!-- graphics elements go here -->
         </g>
       </g>
     </g>
   </g>

Therefore, your example:
><rect width="30" height="30" fill="orange" transform="translate(200,0) 
>rotate(45)"/>

is equivalent to:

   <g transform="translate(200,0)">
      <g transform="rotate(45)">
         <rect width="30" height="30" fill="orange"/>
      </g>
   </g>

Jon Ferraiolo
Adobe Systems, Inc.
SVG 1.0 Editor

At 04:49 AM 12/23/2004, pegan@gresham-forms.co.uk wrote:

>Hi Chris,
>Thanks for the link.
>I have convinced myself that transforms are applied in the 'provided 
>order' (left to right?). I have also just convinced myself that Batik and 
>ASV6 are applying transforms left to right (also in the provided order ?).
>
>In the case of say :-
>
><?xml version="1.0" encoding="UTF-8"?>
><svg width="100%" height="100%" 
>xmlns="<http://www.w3.org/2000/svg>http://www.w3.org/2000/svg">
>     <rect width="30" height="30" fill="orange" 
> transform="translate(200,0) rotate(45)"/>
></svg>
>
>The translate is performed first (origin moves to 200,0) then the rotation 
>of the rectangle at the new origin, thus order is left to right according 
>to the spec and processed by Batik and ASV as per spec.
>
>In the graphics primer you say 'the transform which is applied first 
>appears closest to the vector'. Is the transform that is closest to the 
>vector(s) the first (ie. leftmost) or the last (ie.rightmost) in the 
>transform list ? At the moment I just don't get the right to left bit.
>
>Kind Regards,
>Patrick
>
>
>-----Original Message-----
>From: Chris Lilley [<mailto:chris@w3.org>mailto:chris@w3.org]
>Sent: 23 December 2004 10:43
>To: pegan@gresham-forms.co.uk
>Cc: www-svg@w3.org
>Subject: Re: SVG 1.1 Spec Rec - 7.6 The Transform Attribute
>
>
>On Thursday, December 16, 2004, 6:16:48 PM, pegan wrote:
>
>pgfcu> Hi SVG  WG,
>pgfcu>
>pgfcu> According to 1.1  spec :-
>pgfcu> "The value of the transform attribute is a
>pgfcu> <transform-list>,  which is defined as a list of transform
>pgfcu> definitions, which are applied in the  order provided".
>pgfcu>
>pgfcu> The transform definitions seem to be applied in the
>pgfcu> reverse order to the provided order (ie. right to left) in ASV6
>pgfcu> and Batik.
>
>Yes, they are. To understand why that is correct, you need to look into
>matrix math a little, in particular to understand the terms premultiply
>and postmultiply. I suggest having a look at a computer graphics primer
>on geometry, (just the first chapter), which I wrote a while ago:
>
><http://www.ii.uib.no/undervisning/kurs/v01/i291/i291/geom_sn.pdf>http://www.ii.uib.no/undervisning/kurs/v01/i291/i291/geom_sn.pdf 
>
>
>--
>  Chris Lilley                    <mailto:chris@w3.org>mailto:chris@w3.org
>  Chair, W3C SVG Working Group
>  Member, W3C Technical Architecture Group
>
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