[PD] Timing and PD....

B. Bogart ben at ekran.org
Wed Oct 29 20:56:32 CET 2008

Hey all,

I'm having more and more problems with sync in PD. By sync I mean that
parts of my patches have processing delays that mess up timing. In
general I've been using buffers and delays to keep things working.

This approach is not very scalable.

I find myself using the "timer" object all the time to see if there is a
processing delay I have to worry about. That is in cases where there is
a bang saying an operation is done.

Two examples I'm working on now (in Gem):

First there is a delay between sending a message and the pix_buffer to
store, and then again for pix_buffer_read to read the pixels. The delay
is long enough that trigger does not work, there needs to be a delay to
make sure the image in the buffer is the right one. (sometimes as much
as 200ms)

A second example is that I'm using pix_share and and second PD instance
to offload some CPU usage. Making sure the image sent to that PD
instance and the image received later in the chain is difficult.

I'm not writing for specific advice, hence the generalities, but wanted
to start a discussion on the issue.

What is the long-term solution for PD to solve these issues? Should all
objects that introduce a delay send a bang when they are complete? (for
example pix_buffer? Of course an additional delay occurs when when the
pix_buffer is written to memory and when it gets to the gfx card for

I'm banging my head over these issues a lot lately and wonder if there
is a better approach.

Back to attempting kludging a solution.

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