HermannGrid

% Clear the workspace and the screen
sca;
close all;
clear;

% Here we call some default settings for setting up Psychtoolbox
PsychDefaultSetup(2);

% Get the screen numbers
screens = Screen('Screens');

% Draw to the external screen if avaliable
screenNumber = max(screens);

% Define black and white
white = WhiteIndex(screenNumber);
black = BlackIndex(screenNumber);

% Open an on screen window
[window, windowRect] = PsychImaging('OpenWindow', screenNumber, white);

% Get the size of the on screen window
[screenXpixels, screenYpixels] = Screen('WindowSize', window);

% Query the frame duration
ifi = Screen('GetFlipInterval', window);

% Set up alpha-blending for smooth (anti-aliased) lines
Screen('BlendFunction', window, 'GL_SRC_ALPHA', 'GL_ONE_MINUS_SRC_ALPHA');

% Get the centre coordinate of the window
[xCenter, yCenter] = RectCenter(windowRect);

% Pixel size of the squares and gaps for our Hermann grid
gridSqSize = 100;
gapSize = 20;
stepSize = gridSqSize + gapSize;

% How many can we fit on the screen. Rough hacky code to make sure the
% sqaures do not go off of the screen.
numLines = floor(screenYpixels / stepSize) - 2;
if rem(numLines, 2) ~= 0
    numLines = numLines + 1;
end
halfNumLines = numLines / 2;

% Screen positions for the centre of all of our sqaures
[xpos, ypos] = meshgrid(-halfNumLines:halfNumLines, -halfNumLines:halfNumLines);
xpos = xpos .* stepSize + xCenter;
ypos = ypos .* stepSize + yCenter;

% Dimensions and count
[s1, s2] = size(ypos);
numSquares = numel(ypos);

% Rectangle positions where our squares will go
allRects = nan(numSquares, 4);
ticker = 0;
for i = 1:s1
    for ii = 1:s2
        ticker = ticker + 1;
        allRects(ticker, :) = CenterRectOnPointd([0 0 gridSqSize gridSqSize],...
            xpos(i, ii), ypos(i, ii));
    end
end

% Draw all of the squares
Screen('FillRect', window, black, allRects');

% Flip to the screen
Screen('Flip', window);

% Wait for a key press
KbStrokeWait;

% Clear the screen
sca;