[PD-dev] call for discussion: native video for Pd

[Mathieu Bouchard]

On Sat, 27 May 2006, Miller Puckette wrote:

> I used to think the same thing, that floating-point computation would
> never be feasible on video... but Mathieu has demonstrated that, if you
> schedule the computations carefully, you can do blindingly fast video
> crunching in floating-point.

I don't know where I demonstrated that, cause I never implemented SSE1
support in GridFlow, and I don't know what else would qualify as
"blindingly". Even though GridFlow supports float images since jan.2003, I
didn't use the feature until this year, when I started making video FFTW.
If you want an example of something blindingly fast, look at FFTW (which
uses both SSE1 and great algorithms).

The gap between the speed of floating-point and integer computations has 
been shrinking over the years, but in the last 10 years it has also 
expanded and shrunk back and re-expanded and... it's difficult to know 
where things are heading. I'm sticking with integers as much as I can, 
with small integers whenever it's worth it, and with floats when I have no 
other option (e.g. FFTW).

> much more storage space, so you end up using a lot of memory bandwidth
> (a read or write to external memory costs the same as tens or hundreds
> of CPU cycles these days).

It's difficult to really measure it, because when such a read happens, a
whole chunk is read at once, some of which can be useful later on, if the
cache keeps it long enough, etc. And then, there are often a dozen
instructions running at once in various stages of completion, each taking
a dozen ticks, all documented as single-tick instructions because
engineers figure a dozen divided by a dozen is one. Analysis of
computation time really can't be done the same as it was being done in
1990.

> But anyway, I'll probably make it conditionally compilable in other
> formats so we can just benchmark it and find out for sure.

Yes, I approve that.

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| Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju
| Freelance Digital Arts Engineer, Montréal QC Canada