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Re: transform properties

From: Chris Lilley <chris@w3.org>
Date: Mon, 7 Feb 2011 18:06:21 +0100
Message-ID: <534274879.20110207180621@w3.org>
To: Simon Fraser <smfr@me.com>
CC: Vynce Montgomery <vynce.montgomery@gmail.com>, www-style@w3.org
On Monday, February 7, 2011, 5:54:30 PM, Simon wrote:

SF> On Jan 18, 2011, at 6:51 pm, Vynce Montgomery wrote:

>> I dunno what you guys are doing with transform
>>  (a) please make rotate() positive for counter-clockwise, as it is in
>> mathematics.  This is the opposite of what the (not yet standardized)
>> prototypes in webkit, mozilla, and opera do, but it's still correct.

SF> The clockwise direction was chosen to match SVG:
SF> <http://www.w3.org/TR/SVG/coords.html#RotationDefined>

SF> In addition, on a web page the coordinate system is top-down, so
SF> a clockwise direction is arguably more sensible.

In fact that was why SVG chose a Y-down coordinate system in the first place, because Web pages have a Y-down, top-right-origin coordinate system.

Having chosen that, the direction of rotation (always from positive x axis = 0 degrees to positive y axis = 90 degrees, in mathematics)follows naturally.

 Chris Lilley   Technical Director, Interaction Domain                 
 W3C Graphics Activity Lead, Fonts Activity Lead
 Co-Chair, W3C Hypertext CG
 Member, CSS, WebFonts, SVG Working Groups
Received on Monday, 7 February 2011 17:06:24 UTC

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