Hi,
We are using Psychtoolbox 2.55 on Mac OS 9.2.2
and for some unknown reason, "CopyWindow" is surprisingly slow.
What we are trying to do is pretty basic, so I am hoping
someone with experience with PTB for OS9 can give some suggestions.
I want to display a sequence of gratings on the screen
and I need to load graphics memory with a new grating in just one
frame time.
Here is a method that works running in "Classic" mode.
(1) use SCREEN('PutImage' to copy a sine wave to the top row of
pixels on the screen
this takes about 0.4 msec
(2) use SCREEN('CopyWindow',...,'srcCopyQuickly') to copy this row to
the rest of the screen
replicating the sine wave to make a vertical grating (the src rect
is 1 pixel tall, the dest rect is 768 pixels tall)
this takes about 4.5 msec (less than a video frame time, which is
13.3 msec @ 75 Hz)
Here is the problem:
The exact same code is much slower when I reboot the same machine in
Mac OS 9.2.2
The first step is just as fast.
The second step takes about 39.5 msec ... almost 10 times longer !!
... about 3 video frames to complete the copy
(as a consequence, I see visual "tearing" on the display)
I don't understand why it would be so much slower, since in both
cases it is copying from video memory to video memory.
Does anyone have any suggestions for how to make this work fast in
native OS9?
Do I need updated OS9 video drivers or Quicktime?
...
I can't run my experiment in "Classic" because it does not implement
frame-accurate video synchronization.
Any constructive comments would be appreciated.
-- David Jones
McMaster University
Electrical and Computer Engineering
We are using Psychtoolbox 2.55 on Mac OS 9.2.2
and for some unknown reason, "CopyWindow" is surprisingly slow.
What we are trying to do is pretty basic, so I am hoping
someone with experience with PTB for OS9 can give some suggestions.
I want to display a sequence of gratings on the screen
and I need to load graphics memory with a new grating in just one
frame time.
Here is a method that works running in "Classic" mode.
(1) use SCREEN('PutImage' to copy a sine wave to the top row of
pixels on the screen
this takes about 0.4 msec
(2) use SCREEN('CopyWindow',...,'srcCopyQuickly') to copy this row to
the rest of the screen
replicating the sine wave to make a vertical grating (the src rect
is 1 pixel tall, the dest rect is 768 pixels tall)
this takes about 4.5 msec (less than a video frame time, which is
13.3 msec @ 75 Hz)
Here is the problem:
The exact same code is much slower when I reboot the same machine in
Mac OS 9.2.2
The first step is just as fast.
The second step takes about 39.5 msec ... almost 10 times longer !!
... about 3 video frames to complete the copy
(as a consequence, I see visual "tearing" on the display)
I don't understand why it would be so much slower, since in both
cases it is copying from video memory to video memory.
Does anyone have any suggestions for how to make this work fast in
native OS9?
Do I need updated OS9 video drivers or Quicktime?
...
I can't run my experiment in "Classic" because it does not implement
frame-accurate video synchronization.
Any constructive comments would be appreciated.
-- David Jones
McMaster University
Electrical and Computer Engineering