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% FlipTest
%
% FlipTest times and plots the intervals between flips of the front and
% back display buffers in a tight loop. Flips should occur at the video
% frame period. Result of lipTest are a test of Priority's ability to
% gurantee time to MATLAB for real-time displays.
%
% On OS X, the Screen subfunction 'Flip' replaces 'WaitBlanking' as a means
% of sycnrhonizing updates of video memory with the vertical retrace of your
% monitor. This prevents vertical shearing of displays.
%
% Onscreen windows in OS X are double buffered, having two surfaces:
% front and back. The front surface is memory from which video DACs read
% and is displayed on your montitor. The back surface is video memory to
% which rendering commands draw.
%
% A call to Screen 'Flip' delays until the next vertical retrace, then
% instantaneously interchanges front and back video surfaces, and then
% returns.
% HISTORY
%
% mm/dd/yy
%
% 6/28/04 awi Wrote it.
% 1/11/05 awi Merged in bug fixes given by David Jones.
% Expanded description.
% Give feedback to user in command window.
% Add try ...
try
screenNumber=max(Screen('Screens'));
numFlips = 100;
fprintf('Raising priority for test...\n');
Priority(1);
fprintf('Priority raised.\n')
fprintf('Opening window and flipping frames. This should take about ');
fprintf('%d seconds...\n', ceil(1/Screen('FrameRate',screenNumber) * numFlips));
w=Screen('OpenWindow', screenNumber, [], [], [], 2);
t=[1:numFlips];
GetSecs;
Screen('Flip',w);
for i=1:numFlips
Screen('Flip',w);
t(i)=GetSecs;
end
Priority(0);
fprintf('Priority restored.\n');
fprintf('Test Results:.\n');
Screen('CloseAll');
td=diff(t);
plot(td);
fprintf(' Median frame period: %f seconds\n', median(td));
fprintf(' Max frame period: %f seconds\n', max(td));
fprintf(' Min frame period: %f seconds\n', min(td));
fprintf(' Median frame frequency: %f seconds\n', 1/median(td));
plot(td);
catch
Priority(0);
Screen('CloseAll');
lasterr
end
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