Re: Newbie QC/CI questions - Image delays/Non-GPU code

Core image kernels can't carry any state from one invocation to the next. They can't even test the result of other computations in the same iteration, since the order and the concurrency are not guaranteed by the GPU. To keep data persistent, you have to buffer it, which in Quartz Composer means an Accumulator. I have a couple of examples on my old site (http://www.samkass.com/blog/), such as "ghost" that might help. (I haven't updated anything on my site in a year and a half, so hopefully the compositions still run.)

On Feb 9, 2007, at 5:09 AM, Oliver Donald wrote:

Hi list,

I’ve only been playing with QC and CI for a week or so but as someone who enjoyed hacking up demos back in the Amiga days I’m having great fun! But I’ve got a couple questions that I couldn’t find clear answers to in any of the documentation.

First off, if I have an effect that requires some information to be persistant during a single frame, what is the best way to do this in a CIKernel image unit? I am trying to write a box-blur implementation that scans horizontally and vertically, adding pixels on the right/top and subtracting them from the left/bottom, but I’m not sure how to keep a running total going. How should I do this? Also, is it possible to keep data persistent across frames? I imagine the Accumulator could help but that isn’t very elegant, I’d rather do it in the code.

Secondly, I already asked this but got no answer, if I have a CIKernel image unit that writes values below zero and above 1.0, will these values be preserved or clipped? Will clipping only occur when the image is rendered or will it happen before then?

Thanks,
Oli

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References:
	>Newbie QC/CI questions - Image delays/Non-GPU code (From: "Oliver Donald" <email@hidden>)