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RE: Spec anomaly - opacity

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Tue, 9 Dec 2008 10:41:35 +0000
To: "Glenn A. Adams" <gadams@xfsi.com>, Public TTWG List <public-tt@w3.org>
Message-ID: <90EEC9D914694641A8358AA190DACB3D2FCEA61B90@EA-EXMSG-C334.europe.corp.microsoft.com>

Right. But we refer to [XML Schema Part 2]  3.2.4.1 for the syntactic space of opacity, which is the problem. We should refer to <alphavalue> in CSS3 Values and Units for the syntax of this value like CSS 3 Color does.

Incidentally CSS3 Color latest http://www.w3.org/TR/css3-color/#numerical now uses <alphavalue> in the rgba() expression too; so we need to track that.

"... can either be an <integer>, or it can be zero or more digits followed by a dot (.) followed by one or more digits. Both integers and real numbers may be preceded by a "-" or "+" to indicate the sign, and the sign character is considered part of the <number> value"

Sean Hayes
Media Accessibility Strategist
Accessibility Business Unit
Microsoft

Office:  +44 118 909 5867,
Mobile: +44 7875 091385


-----Original Message-----
From: Glenn A. Adams [mailto:gadams@xfsi.com]
Sent: 09 December 2008 04:04
To: Sean Hayes; Public TTWG List
Subject: Re: Spec anomaly - opacity


We simply refer to the CSS3 Color Module for the value space of opacity and
its semantics. I think we do not want to vary from this, particularly since
other specs, such as SVG, also use these values. DFXP also supports
specifying alpha in RGBA tuples, in which case the value range of [0-255]
applies. There is a straightforward transformation between alpha (A) and
opacity (O) that is easily testable, i.e.,

A = FLOOR ( O * 255 )

and

O = FLOAT ( A ) / 255.0

Glenn

On 12/9/08 7:05 AM, "Sean Hayes" <Sean.Hayes@microsoft.com> wrote:

>
> I notice that opacity is specified as a float value, implying an inordinate
> (and completely untestable) set of gradations of alpha; while colour alpha is
> specified as only 255 steps. This seems completely skewed to me.
>
> I would recommend that we align opacity and colour alpha by specifying <alpha>
> expressions as component-value.
>
> Whether we wish also to anticipate 16bit colour is a separate question we
> probably ought to look at.
>
> Sean Hayes
> Media Accessibility Strategist
> Accessibility Business Unit
> Microsoft
>
> Office:  +44 118 909 5867,
> Mobile: +44 7875 091385
>
Received on Tuesday, 9 December 2008 10:43:37 GMT

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