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Re: Question for CSS 2 developers! - azimuth property

From: Chris Lilley <chris@w3.org>
Date: Thu, 20 Jul 2000 02:48:37 +0200
Message-ID: <39764C65.46954605@w3.org>
To: Bruno <bruno@teraram.com>
CC: www-style@w3.org


Bruno wrote:
> 
> Hello
> 
> I have little question for someone who is responsible for 'azimuth'
> property. I was reading it, and I just could not find explanation what does
> 'behind' mean.

Its a modifier keyword rather than a keyword that is used by itself, and it
means the exact opposite of 'in front', which is the default meaningwhen
'behind' is not specified. More precisely, it is a modifier which produces
a reflection on the 90-270 degree axis. So for example

azimuth: center-right

means 20 degrees, where zero degrees is straight ahead (the way your nose
points) and 90 degrees is the way your right ear points. But

azimuth: center-right behind

means 160 degrees. Its just as far to the right as center-right is, but its
behind you.

> So if someone can explain it to me I would appreciate it.

I hope that helped. I notice that two CSS books that explain this use a
diagram, which would have helped (the books are in French and in Japanese
respectively, which may be relevant because presumably the english-language
keywords were less suggestive of meaning, requiring more explanation). Now
if I could have sent the explanation as a diagram in SVG it would have been
a lot easier ;-)

Oh one more thing, notice the conformance requirement that if an
implementation is unable to produce sounds behind the listener it can
produce them by converting places in the rearwards hemisphere to the
corresponding positions in the forwards hemisphere. For azimuths given as
degrees, there is a formula:

if 90deg < x <= 180deg then x := 180deg - x 
if 180deg < x <= 270deg then x := 540deg - x 

For azimuths given using keywords, you can convert to numbers and apply the
formula. Or you can just drop the 'behind' modifier, which gives the same
result. 


> P.S. for CSS developers - is there any reward for something like this :-)

Fame, if you produce the first fully-conforming implementation - and
adulation, if its open-source as well  ;-)

--
Chris
Received on Wednesday, 19 July 2000 20:48:43 GMT

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