W3C home > Mailing lists > Public > www-style@w3.org > March 2009

Re: [css3-transitions]

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Mon, 30 Mar 2009 16:39:03 +0100
To: www-style@w3.org
Message-Id: <200903301739.03997.Dr.O.Hoffmann@gmx.de>
Giovanni Campagna:
> 2009/3/29 Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>:
> > Hello,
> >
> > these comments are related to
> > http://www.w3.org/TR/2009/WD-css3-transitions-20090320/
> >
> >
> >
> > 1. It is not obvious to me how to specify the values, the
> > transition appears between - ok, the initial value seems
> > to be what is called in SMIL/SVG animations the
> > underlying value, how is the 'to-value' specified?
> > Is it possible to specify a transition from a 'to-value' to
> > the underlying value too?
> > Is it required to use the animation module or another
> > language (like scripting) to specify all this?
> > If another language or scripting is required, this would be
> > disappointing and discouraging for many authors relying on
> > declarative notations for styling and layout and simplicity.
> > Other authors would be forced to create constructions
> > not accessible anymore either without activated scripting or
> > CSS, what would be bad/poor styling.
>
> It seems to me that you missed the meaning of transition: 

I did not find or understand this within the draft/specification,
maybe more complete samples can be useful to improve 
better understanding. Yesterday and today I found some
WebKit samples somewhere around, but this draft should
be understandable on its own.

> a transition 
> happens when the Specified Value of a property that is defined to be
> transitioned is changed. The from value is the previous value of the
> property, the to value is the new value.
> Transitions don't require animations, SMIL or scripting. Just a
> property value changing.
> If you want the opposite transition (from "to" to "from"), just go
> back to the previous value.

About the found samples - this was always CSS for
(X)HTML, roughly about 50% use :hover to change 
something, the other 50% use scripting (therefore 
those 50% did not work at all with
my preferences for unkown pages ;o)
I did not found an example using :focus or :active
of maybe a SMIL/SVG set of a CSS property - does
this cause a transition too or is the effect overwritten
by the higher priority of SMIL/SVG CSS-property
animations?
SVG+CSS samples I created today did not work at
all in the WebKit I have installed (528.16, Safari 4 beta),
neither with :hover nor with setting a property. 

Already this indicates, that it can be very useful, to explain
it better and to provide more examples for better 
understanding for CSS in (X)HTML and SVG.

>
> > 2. It is not obvious to me, how the native CSS works to begin
> > the transition or is this always triggered from outside of CSS
> > or with the onload event of the CSS file?
> > I think, it would be essential especially for authors, who want
> > to use these module to style (X)HTML or XML, to have a
> > native CSS method to start the transition. This is less important
> > for SVG authors, because SVG has already its own more
> > advanced animation methods covering this problem in a
> > convenient way.
> > This SVG/SMIL solution could be a guide, what is required
> > to start transitions.
> > Especially the events activate, beginEvent, endEvent,
> > repeatEvent could already cover a lot of use cases.
> > Device dependent events like click, mousedown, mouseup,
> > mouseout, mouseover, mousemove could be useful too,
> > however they have of course the problem, that they are
> > not accessible, if the user has no pointing device.
> > Another essential feature is the possibility to combine
> > the event with an identifier.
>
> Transitions don't depend on events, they depend on property Specified
> Value changes. This is caused by changing the set of selectors
> matching an element (ie adding a class, a pseudo-class or moving an
> element).
>

Then it could be shown with samples, how values can be changed 
natively within CSS.

For example:

First CSS-file:
div {
transition-property: opacity;
transition-duration: 20s;
opacity:0.5
}
  
Second CSS-file:
div#something {
opacity: 0.9
}

Does it cause a transition 'onload' of the second CSS-file,
especially visible, if the 'onload' of the second CSS-file is
retarded for some reasons by the server for 5s?


Or this:
input#something {
transition-property: transform;
transition-duration: 9s;
transform: rotate(180deg)
 }

input#something:focus
{
transform: scale(-1.2,1.2)
}




Or this one:
a#something {
transition-property: color;
transition-duration: 5s;
color: blue
}

a#something:active
{
color: red
}


Or this one:
div#something {
transition-property: left;
transition-duration: 17s;
position: absolute;
left: 1em;
top: 1em;
}

div#something:hover {
left: 200em;
}

There is no precise definition of :hover concerning
timing of those transitions in the selector section/module.
When does it exactly start, when does it stop?
Trying similar things with WebKit today, this viewer
starts something, when the pointing device
above #something is changed.
However, if only #something is moved away from
the pointing device, this does not mean for WebKit,
that :hover is not applicable anymore. But much
later, when the pointing device is moved again, but
far away from #something, :hover becomes not
applicable anymore and the transitions starts again.
I think, this is not the only possible interpretation
of :hover according how this is specified in CSS.


> > Currently CSS mainly seems to have :hover and :focus
> > to begin or to change something. If we have for example
> > the :hover, is the transition stopped, if :hover does not
> > apply anymore? This could be avoided of course with
> > something like ID.activate or ID.click as begin.
>
> If :hover doesn't apply anymore, and :hover changed a property (and
> started a transition), then the new Specified Value is the one the
> property add before hovering. The property is so transition between
> the current Computed Value (in the middle of transition) and the
> Computed Value found for the new (ie the old) Specified Value.
>

Following discussions between many authors and looking on their
'desires' in the last 10 years, I think, events like ID.activate or ID.click
would be in general useful to be able to change a value - with or without 
a transition and natively in CSS without using another language
like SMIL or a scripting language.



....
>
> > 5. in section 4. it is not noted, how to animate
> > between keywords (they are mentioned
> > in 5. too). This will be the same as for
> > 'visibility'? Or are the keywords always
> > converted into numbers for the current
> > animatable properties (seems to apply
> > only to vertical-align).
>
> Not all properties are animatable (see section 2). I expect that a
> specific section for vertical-align will be included if we want to
> support it (or vertical-align will be modified to find a Computed
> Value being always <length> or <percentage>)

It is noted to be animatable/transitionable already in 5. as
I noted above, including 'keywords' ...

>
> > About paint-server - how to interpolate
> > between a radial and linear gradient?
> > Is the direction vector for linear gradients
> > interpolated too if different? Respectively
> > the cx, cy, fx, fy, r for a radial gradient?
> > What about gradientUnits, gradientTransform,
> > spreadMethod, xlink:href? Or is the interpolation
> > done for each pixel of the output separately?
> > I think, it needs some more explanations
> > how this should work.
>
> Probably only gradients of the same types can be interpolated. 

Maybe, doing it pixel for pixel would be an interesting effect too ;o)

> This is 
> similar with happens with width (you cannot transition from a length
> to a percentage)

Why not? The percentage can be computed at any time to a 
measurable length, if it represents a fraction of a length.
You cannot have a transition between seconds and millimeter
maybe, because both are units for different entities in physics.

>
> > 6. in section 5. Animatable properties
> > the transform property seems to miss,
> > but in 4. it is noted, that this is animatable too.
>
> Again, editiorial
>
> > Why not animation for 'display'? This is already
> > now quite popular to be changed with :hover,
> > I think more than for example 'visibility'
>
> What is the meaning of display in the middle of a transition, eg.
> between block and inline? Inline-block? :D
> Or you want to transition the reflowing caused by display change?

The same applies for visibility, what is indicated to be 
animatable/transitionable ...

....
>
> Next time you start a thread remember to post to "public-fx@w3.org",
> that is the best place for visual effects in CSS / SVG.
>

It is noted in the draft:
"The (archived) public mailing list www-style@w3.org (see instructions) is 
preferred for discussion of this specification."

Should be changed then to the new list as soon as applicable ...


Olaf
Received on Monday, 30 March 2009 15:58:15 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 17:20:17 GMT