Mac Forum / Programming / CodeWarrior / May 2005

You can call it but just don't do it > 60 times per second.  You can
update existing code very easily by adding a lastTimeFlushed variable
to your render loop and then replace:

QDFlushPortBuffer

with:

if(curTime - lastTimeFlushed > 1/60th second) {

  QDFlushPortBuffer;
  lastTimeFlushed = curTime;
}

This isn't the first time the low-level graphics behavior has changed
on the
same hardware after a software update.  But there is some good news.
I'm interested in getting back basic OS 7-9  functionality such as the
ability
to sync to the screen refresh.  The best (only) source of information
on this
topic that I know is the "psychtoolbox" effort.  After a lot of work
they've
had success.

As you've noted CopyBits() and QDFlushPortBuffer() sort of work,
sometimes,
depending, with the latter call blocking until the screen refresh.
Here's what
Allen Ingling of the psychtoolbox group had to say:

"By the way, we tried the carbon copybits calls on OS X for the HIPS
viewer.
Useless on OS X.  Slow transfer rates and unreliably and unverifiable
video synching."

So what they do is set up a high-priority "time contraint" thread and
add
other tricks like killing  the "update" process.  They write to the
back buffer
and there is an openGL call which will will block until the buffers are
flipped.
They report getting reliable syncing to the monitor with jitter in the
100 microsecond range.  It's not solid real-time as you can get under
classic,
but pretty good.

That group has performed a real public service, there's a lot of good
example
code.  They run under matlab, but there is c code which shows how to do
the
basic stuff.

Rob Shaw