W3C home > Mailing lists > Public > www-style@w3.org > November 2001

Re: Opacity 0-1: Bad Idea?

From: Chris Lilley <chris@w3.org>
Date: Mon, 12 Nov 2001 11:16:16 +0100
Message-ID: <3BEFA170.CEB6D5E4@w3.org>
To: lordpixel@mac.com
CC: www-style <www-style@w3.org>

Andy wrote:
> Chris Lilley wrote:
> >
> > Andy wrote:
> > >
> > > No one says "that pane of glass in that window is semi-opaque". It would
> > > always be "transparent" (or translucent!). Its just not English!
> >
> > In fact the term opacity has a long usage in the (English language)
> > computer graphics literature at least back to 1963, and probably
> > further.
> Well, yes indeed. Of course its valid English, its just not the way
> anyone would ever actually speak. 

Computer graphics artists are, in fact, people ;-)

> I admit I would make my argument more convincing if I'd have omitted the
> hyperbole implied by saying "Its just not English!". I probably deserved
> to be jumped on for that.

Not jumped on, but it wasn't too convincing.

> > Secondly, the property is already in a W3C Recommendation (SVG 1.0), it
> > is thus final; and being included into CSS3 to allow its use in areas
> > other than purely graphical.
> > http://www.w3.org/TR/SVG/masking.html#OpacityProperty
> OK, I missed the SVG link (as J David Eisenberg pointed out, it makes
> more sense with respect to image formats, where folks do "think
> backwards" due to the way alpha channels are usually defined).

They don't think backwards. They don't think forwards either; they just
use a long-established term of art whichhas now, finally, made it into a
W3C Rec and is being proposed for adoption in a wider (text-based)

> J David also proposes supporting both percentages and units, and both
> opacity and transparency, thus covering both compatibility with SVG and
> the way people think in real life.

No. Sorry, that does not provide 'compatibility' at all. Consider a
multi-namespace XML document where parts are in some namespace that uis
being styled textually using the CSS box model and parts are in the SVG
namespace and being styled as SVG. Consider particularly  the case where
the root of the document A is textual, it has a child tree B in SVG
which in turn has a child tree C which is textual. For example, C is a
callout B is a diagram and A is a manual. Now, if I have an opacity
property (or a transparency property that somehow interacts with it) set
on A and it inherits right down to C - what is the computed value at all

> > Thirdly, there are already a substantial number of implementations of
> > this property, in both renderers and authoring tools.
> -moz-opacity? That's deliberately in a private "namespace" particularly
> so that it will be forwards compatible with CSS3.

No. I was referring to opacity, the W3C Recommendation definition

> I don't doubt there
> are other implementations other than that one, but how many of these
> tools are widely used enough to influence the direction of the spec?

I live in hope that, maybe in five to ten years, some folks might
realise that there is more to life than HTML browsers.....

The implementations of opacity that I am aware of (and there was already
mention of one more in this thread that I was not previously aware of)

Rendering implementations:

- ibm svg viewer
- adobe svg viewer
- csiro svg browser
- jackaroo svg viewer
- ilog jviews component suite
- ionic svg rendering toolkit
- jasc webdraw native svg editor
- batik svg toolkit
- sodipodi svg browser editor
- bitflash svg/wap displayer
- itedo isodraw 5
- corel draw 10 editor
- adobe illustrator 10 editor
- x-smiles multi-namespace XML browser
- csiro pocket pc svg viewer
- kdd labs jaMaPs service
- amaya multi-namespace XML browser/editor
- real one multi-namespace XML player
- mozilla svg project (svg branch)
- oratrix multi-namespace authoring tool

Non-rendering implementations:
- mayura draw svg export
- beez animation tooklkit
- sketch
- CadStd Pro
- GraPL
- oak draw
- sphynx open editor
- ims web engine
- celinea cr2v
- sun slidemaker toolkit
- DBx Geomantics SVG mapmaker
- kvec
- software mechanics SVGmaker
- fdsSVG
- elansoft agileblox
- ibm cgm to svg transcoder
- roit SVG.pm
- savage software dataslinger

The majority of these are svg-only, but some are also allowing opacity
to be used in non-svg contexts in the same tree, now that its definition
is nailed down and that it is merely a case of including it or not in
CSS3 for non-graphical uses.

Received on Monday, 12 November 2001 05:16:16 UTC

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