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Re: transitions vs. animations

From: Chris Marrin <cmarrin@apple.com>
Date: Mon, 05 Apr 2010 10:07:15 -0700
Message-id: <F6A58BB1-1CF5-498A-AC82-2A21D654C0B4@apple.com>
To: "www-style@w3.org list" <www-style@w3.org>

On Apr 4, 2010, at 4:37 PM, Perry Smith wrote:

> On Apr 4, 2010, at 3:12 PM, Tab Atkins Jr. wrote:
>> On Sun, Apr 4, 2010 at 11:23 AM, Perry Smith <pedzsan@gmail.com> wrote:
>>> Perhaps instead of calling them 'states' or 'state changes', call them
>>> 'events'.  I'm new to this list so I don't understand Håkon's statement,
>>> "We'd like to do this without adding an event model to CSS."  It may be that
>>> my way of thinking opens a can of worms that has already been discussed.
>>> First, it solves Simon's concerns because the event would not happen when a
>>> class is added or removed.
>> It doesn't solve the concerns so much as eliminate them, because it
>> makes transitions much weaker.  A lot of transition usage will be
>> based on :hover, :focus, etc., but a lot of it *won't* be.  There are
>> tons of places in code that I've written where I'd like to animate
>> some property change triggered by me swapping classes.
>> Simon points out, correctly, that trying to hack an event model that
>> responds to arbitrary selector matching changes would turn super-crazy
>> very quickly.  Both in terms of simple mechanics, and in terms of what
>> authors have to keep track of (the 'combinatorial explosion' he
>> mentions).
> I clearly don't understand the objective.
> If the user already is using javascript to change classes, then he can define the animations like script.aculo.us and others do.
> I thought the desire was to have something so, lets call them "graphic artists", can use without knowing or mucking with JS.  Someone used the term "declarative".  I took that to mean something I can declare in CSS alone.

There is much more than just the convenience of a declarative form here. One of the biggest motivators for Transitions and Animations was to create a system that could perform animations in hardware. On embedded platforms, running Javascript timers and rerendering the entire page for each step quickly becomes expensive enough that framerates become unacceptably slow. 

Received on Monday, 5 April 2010 17:07:48 UTC

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