determining the result of a CAAnimation instance for time 't'

  • Hello all,

    Another Core Anim question.

    I'd like to be able to determine the result of any CAAnimation
    instance, given time 't', assuming that 't' is some time between the
    animation.beginTime and (animation.beginTime + animation.duration).
    The idea being, that I want to apply whatever modifications that an
    animation represents to my layer - then draw/render a single frame.  I
    do not want the animations to 'run' like normal.

    Here's the 'use case' for this:
    An arbitrarily complex layer containing animations is being drawn into
    a view.  A slider is being used to scrub backward and forward in time,
    and the view draws one single frame based on the time represented by
    the slider.  Any CALayer animations included in the layer tree must
    therefore also be taken into account and applied to the layer before
    the frame is rendered.

    Here's the problem as I see it:
    Core animation layers simply 'run' when they are added into the layer
    tree, applying modifications to the presentation layer in the
    background.  There isn't a way to control their time as such.  Sure,
    one can define their beginTime and duration, but controlling exactly
    *when* they fire/apply their effect is another matter.

    I have made a spike solution already that controls the
    "transform.scale" property of a CALayer over time.  It works well,
    however:

    During the rendering of each frame, I disable animation on the layer,
    spin through all the CABasicAnimation instances, and then use a
    *private* method on CAMediaTimingFunction to solve for an input time
    (between 0 and 1).  This provides me a %age complete value (of the
    timing function that is), which is then used to determine 'how far
    along' the animation we are.  Then I create a CABasicAnimation,
    compute its values, and apply that single animation [of a keypath] to
    the layer tree.

    It works well - my issues with this method are:

    1) first and foremost, I'm using a private method - which I don't want
    to do in production code (many other discussion exist about this - I
    don't really want to duplicate them here)

    2) it feels inefficient, because I am having to recompute the results
    of CAAnimation instances for each frame, and I'm concerned as to how
    this will scale.  Then again, I've got no hard data/performance stats
    to support my thoughts in this arena.

    So my question is; does anyone have an idea of how I could do this
    *without* using a private method?

    The method in question is:
    // used SymbolExplorer to get this...
    @interface CAMediaTimingFunction (CAMediaTimingFunction_PrivateMethods)
    - (float) _solveForInput:(float)pcnt;
    @end

    Thanks in advance,

    -
    john clayton
    http://www.coderage-software.com/
  • Hi John,

    I am already using CARenderer to render a layer into a CAOpenGLLayer
    (because I want to composite my results further), the problem comes
    when I want to render at any arbitrary time point, either in the
    future or in the past - in conjunction with animation.

    Animations in a layer begin running, effect the presentation layer
    over time, and then 'expire' on their own (optionally removing
    themselves from the animation tree).

    The example you provided (which is great by the way!  thanks!)
    achieves exactly the effect I am looking for, with one catch.  I don't
    have the luxury of setting the repeatCount of the animation to a
    really huge number.  In my use case, that'd basically make all
    animations stretch on for eternity, and overlap each other.

    If I set the repeatCount to 1 (or delete that line entirely), then the
    example animates correctly, once, in the forward direction.  This is
    correct of course.  The animation as it stands removes itself from the
    hierarchy and when I drag the slider backwards nothing (of course)
    happens.  It does not matter if I tell the animation not to remove
    itself either, because it won't 'restart' itself ever again - because
    CACurrentMediaTime() marches forward, never backwards.  (does that
    make sense what I just wrote there btw?).

    This is the problem I'm trying to crack :-)

    Also: I agree re: private methods - its a no no.

    I was wondering if I could hold copies of animations, and insert those
    into the layer tree with appropriate negative timeOffset values,
    perform a render then remove the animations.  That'd mean I get the
    full benefit of the CA library interpolation routines... I'll
    experiment with that idea and write a reply to this message with the
    results.

    -
    john

    On 28/11/2007, at 6:39 PM, John Harper wrote:

    > Hi,
    >
    > have you looked at the CARenderer class, it was added to support the
    > kind of thing you're trying to do – drive the renderer timing by
    > hand, and should be much faster.
    >
    > Here's a simple project that does that:
    >
    > <RendererSample.zip>
    >
    >
    > As for evaluating timing functions, you shouldn't use undocumented
    > functions. In this case there's no need to, you can fetch the
    > control points from the function and use a numerical root-finding
    > method to solve the function for a given input or output time, e.g.: http://en.wikipedia.org/wiki/Newton%27s_method
    >
    > John
    >
    >
    > On Nov 27, 2007, at 9:50 PM, John Clayton wrote:
    >
    >> Hello all,
    >>
    >> Another Core Anim question.
    >>
    >> I'd like to be able to determine the result of any CAAnimation
    >> instance, given time 't', assuming that 't' is some time between
    >> the animation.beginTime and (animation.beginTime +
    >> animation.duration).  The idea being, that I want to apply whatever
    >> modifications that an animation represents to my layer - then draw/
    >> render a single frame.  I do not want the animations to 'run' like
    >> normal.
    >>
    >> Here's the 'use case' for this:
    >> An arbitrarily complex layer containing animations is being drawn
    >> into a view.  A slider is being used to scrub backward and forward
    >> in time, and the view draws one single frame based on the time
    >> represented by the slider.  Any CALayer animations included in the
    >> layer tree must therefore also be taken into account and applied to
    >> the layer before the frame is rendered.
    >>
    >> Here's the problem as I see it:
    >> Core animation layers simply 'run' when they are added into the
    >> layer tree, applying modifications to the presentation layer in the
    >> background.  There isn't a way to control their time as such.
    >> Sure, one can define their beginTime and duration, but controlling
    >> exactly *when* they fire/apply their effect is another matter.
    >>
    >> I have made a spike solution already that controls the
    >> "transform.scale" property of a CALayer over time.  It works well,
    >> however:
    >>
    >> During the rendering of each frame, I disable animation on the
    >> layer, spin through all the CABasicAnimation instances, and then
    >> use a *private* method on CAMediaTimingFunction to solve for an
    >> input time (between 0 and 1).  This provides me a %age complete
    >> value (of the timing function that is), which is then used to
    >> determine 'how far along' the animation we are.  Then I create a
    >> CABasicAnimation, compute its values, and apply that single
    >> animation [of a keypath] to the layer tree.
    >>
    >> It works well - my issues with this method are:
    >>
    >> 1) first and foremost, I'm using a private method - which I don't
    >> want to do in production code (many other discussion exist about
    >> this - I don't really want to duplicate them here)
    >>
    >> 2) it feels inefficient, because I am having to recompute the
    >> results of CAAnimation instances for each frame, and I'm concerned
    >> as to how this will scale.  Then again, I've got no hard data/
    >> performance stats to support my thoughts in this arena.
    >>
    >> So my question is; does anyone have an idea of how I could do this
    >> *without* using a private method?
    >>
    >> The method in question is:
    >> // used SymbolExplorer to get this...
    >> @interface CAMediaTimingFunction
    >> (CAMediaTimingFunction_PrivateMethods)
    >> - (float) _solveForInput:(float)pcnt;
    >> @end
    >>
    >>
    >> Thanks in advance,
    >>
    >> -
    >> john clayton
    >> http://www.coderage-software.com/
    >
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