Re: [css3-2d-transforms] Unit for e and f in matrix(a,b,c,d,e,f)

This has been raised a number of times:
<https://www.w3.org/Bugs/Public/show_bug.cgi?id=15628>
<http://lists.w3.org/Archives/Public/www-style/2009Oct/0360.html>

and is on the F2F agenda for today.

Simon

On Feb 8, 2012, at 11:39 AM, Simon Sapin wrote:

> Hi,
> 
> The syntax for a matrix transformation in the current ED is:
> 
>    matrix(<number>, <number>, <number>, <number>, <number>, <number>)
> 
> The meaning is defined in the SVG spec:
> http://www.w3.org/TR/SVG/images/coords/MatrixMultiply.png
> 
> From this definition, it is apparent that a, b, c and d in matrix(a,b,c,d,e,f) are multiplied by a length and give a new length, so they are unit-less numbers. However, e and f are multiplied by a unit-less one and give a length, so they are lengths too.
> 
> What is the unit for e and f? I can’t find this defined in the spec. SVG gets away with it since unit-less numbers are valid lengths there, but this is not the case in CSS.
> 
> 
> Quick test: (prefix as appropriate and change the 5em value)
> 
> data:text/html,<div%20style="transform:matrix(1,0,0,1,0,5em)">Hello
> 
> Chromium 16 only accepts <number> and reads it as 'px'. Firefox 10 accepts both <number> (as px) and <translation-value>.
> 
> 
> I think one of these should be done:
> 
> 1. Keep e and f as unit-less numbers in the syntax, but specify that they are interpreted as length in some specific unit. Choosing the 'px' unit would be most consistent with SVG.
> 
> 2. The syntax for matrix() is changed to take explicit units:
> 
>    matrix(<number>, <number>, <number>, <number>,
>           <translation-value>, <translation-value>)
> 
> 3. Both: make the syntax something like <number> | <translation-value> for e and f, and specify the unit for <number>.
> 
> 
> Regards,
> -- 
> Simon Sapin
>

Received on Wednesday, 8 February 2012 11:06:17 UTC