Re: [linux-audio-dev] LADSPA and run_adding()

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Subject: Re: [linux-audio-dev] LADSPA and run_adding()
From: Paul Sladen (paul_AT_sladen.org)
Date: Tue Nov 21 2000 - 01:31:29 EET


On Mon, 20 Nov 2000, Roger Larsson wrote:

> On Sunday 19 November 2000 12:49, David Olofson wrote:
> > On Sat, 18 Nov 2000, Kai Vehmanen wrote:
> > > On Fri, 17 Nov 2000, Paul Barton-Davis wrote:
> > > > I have to laugh - here's the exact opposite point of view from
> > > > vst-plugins today, about processReplacing, which is the equivalent of
> > >
> > > [...]
> > >
> > > > Can both points of view be right ?
> > > >
> > > :) Yup, been following the same vst-plugins thread. But seriously,
> > >
> > > this guy is just comparing run_adding() and run_replacing() using one
> > > use case.
> >
> > Yep. And we actually have three situations to take into consideration
> > here;
> >
> > 1) plugin taking data from one buffer, mixing into another
> >
> > 2) plugin taking data from one buffer, overwriting another
> >
> > 3) plugin taking data from a buffer, while overwriting it
> >
> >
> > The third case is what breaks some of the reasoning behind switching
> > to run_adding() as the default. run_adding() requires extra buffer +
> > zero operation in chains (3), whereas run() requires extra buffer +
> > add in mixers (1). run_adding() also requires an extra zero operation
> > to overwrite a buffer (2).
> >
>
> With run_replacing you may do 3) in chains with only one buffer !
> If the engine that allocs buffers know that a plugin is never looking
> back - impossible with run_adding !!!
>

The difference is, that the audio-server/host can *patch up* for the
plugin only suppling run_adding()... not so, when you only provide the
facility to overwrite the current buffer. The server knows that all it
has to do is to add a call to "zero" before execution the plug.

Paul

--
e: paul_AT_sladen.org   t: 0115 922 7162


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