/usr/share/psychtoolbox-3/PsychTests/DatapixxGPUDitherpatternTest.m is in psychtoolbox-3-common 3.0.12.20160126.dfsg1-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 | function DatapixxGPUDitherpatternTest(fullscreen)
% DatapixxGPUDitherpatternTest([fullscreen=1])
%
% Low level diagnostic for GPU dithering via Datapixx.
%
% Steps through all 256 grayscale levels and uses
% Datapixx et al. scanline readback to check what
% the GPU actually outputs. Plots it and prints
% the first 10 pixels of the topmost output scanline.
%
% This is meant to facilitate low-level diagnosis
% of GPU dithering bugs if our regular test script
% BitsPlusIdentityClutTest.m reports dithering trouble
% and can't fix the problem automatically.
%
% 'fullscreen' Defaults to 1 for fullscreen windows.
% 0 = Use a windowed window at top of screen for
% display to also diagnose possible compositor
% interference.
%
% History:
% 13-Aug-2015 mk Wrote it.
PsychDefaultSetup(0);
Datapixx('Open');
if nargin < 1 || isempty(fullscreen)
fullscreen = 1;
end
screenid = max(Screen('Screens'));
if fullscreen
rect = [];
else
rect = [0, 0, Screen('WindowSize', screenid), 90];
end
w = Screen('Openwindow', screenid, 0, rect);
LoadIdentityClut(w);
even = zeros(1,256);
odd = even;
for i = 0:255
Screen('FillRect', w, i);
Screen('Flip', w);
Datapixx('RegWrRdVideoSync');
Datapixx('RegWrRdVideoSync');
Datapixx('RegWrRdVideoSync');
pixels = Datapixx('GetVideoLine');
pixels = pixels(1,1:10);
fprintf('Ref %i: ', i);
fprintf('%i ', pixels);
fprintf('\n');
even(i+1) = pixels(1,1);
odd(i+1) = pixels(1, 2);
end
Datapixx('Close');
sca;
close all;
plot(0:255, even, 'r', 0:255, odd, 'g');
return;
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