Hello Chilton
It's not really the interpolator that's causing the CPU usage - it's
the whole composition.
What's happening is that the interpolator is driving the animation, so
while that's working, the CPU has to also calculate the line
positions, handle rendering etc. When you remove the interpolator (or
disconnect it), no animation happens, and QC doesn't do anything at
all (hence CPU usage falls to near zero - it's waiting for something
to do).
The reason why the duration has no effect on CPU time is simple -
you're asking it to interpolate between two values over a certain
duration. It still has to calculate the current position every frame
though, so it's going to use the same CPU time each frame. It makes no
difference if the animation moves slow or fast on screen, the computer
still has to draw a picture 60 times a second to make it look smooth.
To reduce CPU usage, you need to change the frame rate (it's normally
set to 60, but you can change it in the prefs). Less frame rate = less
work to do, but it won't look good in most cases.
Really though, 8.5% CPU usage isn't a lot. You shouldn't worry about
it unless you're writing something where performance is really
critical, or it's hitting 100% and running slowly.
Chris
On 3 Sep 2009, at 01:18, Chilton Webb wrote:
Hi!
Here's the thing--I've noticed that some of the simplest animations
in QC seem to suck up an enormous amount of CPU time, for what
little they appear to do. If this was my own code, I'd know how to
fix it. But with things like the interpolator, I'm not entirely
clear how I should even start to fix things like this. Any
suggestions would be greatly appreciated!
So I did some experimenting. What this video shows are the areas I'm
most concerned with...
http://www.conjurebunny.com/QuartzCompositionCPUUsage.mov
I have a simple composition that draws some lines, and uses a single
interpolator to move the lines around.
At the start, I have 8.5% of my CPU time taken up by the
interpolator. It's set to have a duration of '2'. Which yields a
really, really fast animation.
When I remove the connection to the interpolator, the CPU time drops
to 0.3 % or so. Which is expected. No mysteries there!
Next I wire it back up, and bump the duration to an incredibly high
number. Now I have the same CPU % usage that I had before! That's
the first thing that doesn't make sense. I would have expected it to
at least use less CPU time, as the duration increases.
Does this mean that the QC runs on some internal timer that runs at
a fixed rate? If so, can I alter the speed of the internal timer?
Marching on...
Next I wire up the interpolator to three other sets of lines. The
CPU time jumps up to a much higher number. Remember though, the
interpolator is still set to a really high number.
After this is done, the CPU time sticks around 25%.
And I can kinda understand it up to this point, assuming there's
some internal timer that is used that is independent of everything
else. But...
The last thing I do is set the interpolator back to '2'.
The CPU time drops back down to around 1% faster than it was at the
very beginning (around 8.7 - 9.5 % CPU time), when it only had one
set of lines to draw.
That makes no sense to me. Why would it use MORE CPU time if it's
generating less, and less time when it is generating more?
Any suggestions greatly appreciated!
Thank you!
-Chilton
ConjureBunny.com
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