Re: determining the result of a CAAnimation instance for time 't'
Re: determining the result of a CAAnimation instance for time 't'
- Subject: Re: determining the result of a CAAnimation instance for time 't'
- From: John Clayton <email@hidden>
- Date: Wed, 28 Nov 2007 22:42:48 +0100
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's_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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