[PD] how to iterate over left and right channel separately in one Pd class?

[katja]

Hi Miller,

Thanks for the solution. The routines are in place so copying the
right channel input to output should do it. Is there any reason to
prefer copy_perform() over memcpy()? I'm trying to make the most
efficient reverb for RPi & Co.

Katja



On Fri, Jan 11, 2013 at 7:57 PM, Miller Puckette <msp at ucsd.edu> wrote:
> Hi Katja -
>
> There's one example of this in sigfft_dspx() - a complex FFT that 'natively'
> works on 2 signals in-place but has to deal with various cases in which
> buffers get re-used.  It's ugly but the basic idea is first to get the
> inputs copied to the outputs (unless they're already there in the correct
> order in which case nothing needs to be done) and then run the in-place
> algorithm.
>
> If the algo only works out-of-place (i.e. you need 4 distinct buffers, 2
> in and 2 out) the only way out is (at least conditionally) allocate temporary
> copies of the inputs before writing to any outputs.
>
> I may be able to add an optional way tilde objects can request that output
> buffers be distinct from input ones sometime in the future - but this is a
> couple of steps away for me right now :)
>
> M
>
> On Fri, Jan 11, 2013 at 03:32:09PM +0100, katja wrote:
>> Hello,
>>
>> I'm working on a Pd class with stereo channels (reverb), and the
>> routine happens to be most efficient when iterating over the samples
>> per channel, instead of left and right together in the perform loop.
>> However, when doing two while loops in one object, one for left and
>> one for right, the right channel samples get overwritten because of
>> sample-wise in-place computation. Is this an inescapable truth? I
>> mean, I could write a left channel class and a right channel class
>> (actually did that to verify that it works), but it's inconvenient to
>> use. What could be an efficient way to get them in one object?
>>
>> Thanks,
>> Katja
>>
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