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Re: [CSS4 color][CSS4 transition] color pre-multiplied vs non pre-multiplied was (Re: [CSSWG] Minutes TPAC Tue 2012-10-30 AM I: Abstract Directions, Transforms, Transitions)

From: Alan Gresley <alan@css-class.com>
Date: Tue, 05 Feb 2013 15:29:16 +1100
Message-ID: <51108A9C.9000503@css-class.com>
To: Rik Cabanier <cabanier@gmail.com>
CC: Brad Kemper <brad.kemper@gmail.com>, Simon Fraser <smfr@me.com>, fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>
On 5/02/2013 3:08 PM, Rik Cabanier wrote:

> No, it's different (see attached)
> In order to emulate the bottom gradient, you need to create an extra color
> stop under the hood.

Thank you (I did correct myself). This is what I said well over a year 
ago (July 2011 to be precised). At the time, an implementer said that I 
was wrong about the creation of an extra color stop [1]. I was only 
wrong with rgba(255,0,0,0) 50% and rgba(0,0,255,0) 50%. I quote the 
response below.

It would be good to have a open discussion about this. I have 
demonstrated many gradient effects that can only been done in non 
pre-multiplied colorspace.

On Fri, Jul 29, 2011 at 5:39 AM, Alan Gresley <alan@css-class.com> wrote:
 > The way Opera interpolates this gradient,
 >   linear-gradient(red, transparent, blue)
 > suggest that internally, a double color stop (as shown below) is 
 >   rgba(255,0,0,0) 50%, rgba(0,0,255,0) 50%
 > So in affect, the keyword 'transparent' is already behaving as a switch.

No.  Internally, the colors are interpolated in premultiplied space.
There is no switch or duplication of color-stops.

1. http://lists.w3.org/Archives/Public/www-style/2011Jul/0532.html

Alan Gresley
Received on Tuesday, 5 February 2013 04:29:45 UTC

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