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List:       kde-panel-devel
Subject:    Random ideas about grouping js animations
From:       Adenilson Cavalcanti <savagobr () yahoo ! com>
Date:       2010-06-22 2:29:51
Message-ID: 64922.10051.qm () web53804 ! mail ! re2 ! yahoo ! com
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Dear Friends

The purpose of this message is to discuss some ideas and ask for input of plasma \
developers concerning how to group javascript animations (jsanims).

IIRC, last month a new factory of animations landed in trunk: Plasma::Animation \
Animator::create(const QString &animationName, QObject *parent = 0);

What it does is quite nifty: it allows to specify an animation type by name and let \
the theme to load an external js code that defines it. The motivation for this plus \
some benchmarks can be found in my blog (but in short we can have themable animations \
plus write new animations in javascript without noticeable execution speed changes).

But an important feature is missing: allow a js animation to define itself as group \
of other animations (being C++ or js).

Today is possible to create (n*jsanim) objects and group them in a QAnimationGroup \
(being linear or parallel). I tested this in C++, but I assume that the bindings for \
animation groups in js should work as well. 

What is missing is to add that bindings in the QScriptEngine singleton used by \
JavascriptAnimation class. So, grouping should be easily achievable (... famous last \
words...) in js client side.

Last week I was thinking about how to solve the remaining part of the puzzle (i.e. \
allow an jsanim to define itself by grouping other animation objects) and came with \
the following self excluding approaches:

a) jsanim 'class' access the 'updateCurrentTime' function of other objects while \
running the animation loop. So looking at an jsanim example:

function ZoomAnimation(target, duration) {
    this.target = target;
    this.duration = duration;

    this.updateCurrentTime = function(currentTime) {

	var delta = currentTime/this.duration;
	this.target.scale = delta;

    }
}


The composed new jsanim 'class' would require to access the plasma animation factory \
and set as an attribute of itself 'n' instances of other animations. Then in the \
'updateCurrentTime', it would explicitly call each animation instance \
'updateCurrentTime' method. E.g

function AppearAnimation(target, duration) {
    this.target = target;
    this.duration = duration;
    //We need to have the factory exported to the QScriptEngine!
    this.zoom = new ZoomAnimation(target)
    this.pulse = new PulseAnimation(target)
}


The advantage here is that we have fine control over the execution of the composed \
animation, but having linear X parallel behavior would require some extra logic \
(mostly check for the elapsed time and decide to call or not the 'updateCurrentTime' \
of the internal animations). To make this clearer, here it goes some pseudocode (I \
hope that indentation will not break when I click 'send' the message...)

//Linear
    this.updateCurrentTime = function(currentTime) {

	var delta = currentTime/this.duration;
        //First execute zoom
	if (currentTime < 100)
              this.zoom.updateCurrentTime(delta)
        else //Later the pulse for the remaining time
              this.pulse.updateCurrentTime(delta)

    }

//Parallel
    this.updateCurrentTime = function(currentTime) {

	var delta = currentTime/this.duration;
        //Execute both at 'same' time
        this.zoom.updateCurrentTime(delta)
        this.pulse.updateCurrentTime(delta)

    }

Of course, guaranteeing that rewinding the animation will result into something that \
actually makes sense might require some extra logic for some animations (as we have \
in some of the C++ ones).

Ok, so let's move on to the next alternative


b) jsanim is just an animation group: and in its creation, it sets as a self \
attribute an animation group instance with the other objects that it wants to use. I \
can see that this might work, but honestly, I'm not very attracted to this approach \
and will not detail how it could be implemented...


So, what you guys think about this subject? Please feel free to send another \
proposals for addressing the issue (more alternatives are always good).


Best regards


Adenilson Cavalcanti
a.k.a. Savago


      
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