Re: Host callback
Re: Host callback
- Subject: Re: Host callback
- From: Howard Moon <email@hidden>
- Date: Thu, 3 Mar 2005 07:10:19 -0800
Hi all,
I thought I'd better chime in here about the specific example given
below:
On Mar 2, 2005, at 3:37 PM, Pavol Markovic wrote:
Hi Ralph,
here's example. The only relevant place/frequency to call callback
functions is in render/process thread, max once per render call (you
don't have to call it for every single frame, because the number of
frames to render are passed as parameter into render method/function)
... somewhere in render/process call stack...
bool haveSamplePos = false;
Float64 outCurrentSampleInTimeLine;
if ( IsTransportStateProcSafe() &&
mHostCallbackInfo.transportStateProc )
{
OSStatus result =
mHostCallbackInfo.transportStateProc(mHostCallbackInfo.hostUserData,
NULL, NULL, &outCurrentSampleInTimeLine, NULL, NULL, NULL);
Unfortunately, neither Logic nor Digital Performer currently give valid
information for the outCurrentSampleInTimeLine parameter. You'll just
get the value 0 for that. Other information should be valid, but the
time in samples may not be, depending on the host. This has been a
major headache for our software. It's strange that the callback was
implemented, but the proper setting of one of the parameters left out.
For hosts that give us 0 in that parameter, we're relying on the
(potentially much less reliable) time information in the Render call.
if ( result == noErr )
{
haveSamplePos = true;
}
}
Please note, that currently very few hosts provide this info and older
versions of GarageBand and Logic may crash when tryin' to call this.
Find e-mail thread "TransportState Logic/GarageBand workaround" in
archives (8/18/2004).
Quite so. But you'd think that once a host (esp. one that Apple owns!)
added the callback support, they'd add *all* the information it
purports to support. (The only AU host I have that supports the time
info is Metro. At least *someone* got it right! :-))
-Howard
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