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Re: opacity, animate and mask

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Fri, 3 Aug 2007 16:39:17 +0200
To: j.chetwynd@btinternet.com, www-svg@w3.org
Message-Id: <200708031639.17312.Dr.O.Hoffmann@gmx.de>

Hello,

from my personal point of view, this is a matter of taste,
if it is not handled as an opaque object, one needs 
another attribute or property to allow authors to
define, at which fraction of opacity the object cannot
receive any events anymore, see for example
the SMIL3 draft:

http://www.w3.org/TR/2007/WD-SMIL3-20070713/smil-extended-media-object.html#smilMediaNS-MediaOpacity

Well, the opaque glass plate methaphor fits to the
current behaviour, the thickness not, thats the
reason, why I choose it ;o)
And to be fussy with the methaphor of thickness -
if there is still an SiO2 around somewhere, if there is
some dust or sand around, the thickness cannot really
assumed to be completely zero ;o)
On the other hand, you will already manage to grab
through it, if it is very thin, a mono-layer of atoms/molecules 
or something, therefore an additional attribute or
property is required for this methaphor to decide,
when you are able to grab through it, as it is specified
in the SMIL 3 draft.


Concerning opacity and animation it would be a little
bit surprising, if an object can receive events for
opacity in the range (0,1] and only for 0 it cannot 
receive any events? Why not to choose:
[0, 0.03141) no events and for [0.03141, 1] events possible?
I think to say it can receive events for any opacity
value simplifies the situation for implementors, they do
not have to look for details or have to imagine sophisticated
methaphors, especially within an animation. And for authors 
it is no problem to add an additional set animation for 
pointer-events or in the case of opacity 0 for display to 
'remove' the object completely. This set animation can be 
timed with the opacity animation too with syncbase values.
Therefore I cannot see that this restricts my
possibilities as authors to realise what I need.
The method as introduced in the SMIL3 draft
is clearly an improvement for authors of SMIL3, but 
not really important for SVG 1.1, because there are
(several) other possibilities to get a similar effect and
to decide which object in a stack will receive an event
at which time...


>
> there are many possible similes but why chose the opacity of a glass
> plate?
> why not it's thickness for instance?
>
> No one has so far contributed a use case, where this behaviour is
> essential or even desirable, whereas the uses of the contrary
> position seem natural, as for instance fading linked images...
>
> regards
>
> Jonathan Chetwynd
>
Received on Friday, 3 August 2007 14:45:13 GMT

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