psychtoolbox-3-common 3.0.9+svn2579.dfsg1-1 / usr / share / psychtoolbox-3 / PsychDemos / GratingDemo.m

function GratingDemo
% GratingDemo
%
% Displays a stationary grating.  See also DriftDemo, DriftDemo2, DriftDemo3 and DriftWaitDemo.

% ---------- Program History ----------

% 07/01/1999 dgp Added arbitrary orientation.
% 12/10/2001 awi Added font conditional.
% 02/21/2002 dgp Mentioned DriftDemo.
% 04/03/2002 awi Merged OS9 and Win versions, which had fallen out of sync. 
% 04/13/2002 dgp Used Arial, eliminating need for conditional.
% 07/15/2003 dgp Added comments explaining f and lambda.
% 08/16/2006 rhh Added user-friendly parameters, such as tiltInDegrees,
%                pixelsPerPeriod, periodsCoveredByOneStandardDeviation and widthOfGrid.
% 08/18/2006 rhh Expanded comments and created comment sections.
% 10/04/2006 dhb Minimize warnings.
% 10/11/2006 dhb Use maximum available screen.
% 10/14/2006 dhb Save and restore altered prefs, more extensive comments for them
% 07/12/2006 prf Changed method of rotating the grating

% ---------- Parameter Setup ----------
% Initializes the program's parameters.

% Prevents MATLAB from reprinting the source code when the program runs.
echo off

% *** To rotate the grating, set tiltInDegrees to a new value.
tiltInDegrees = 7; % The tilt of the grating in degrees.
tiltInRadians = tiltInDegrees * pi / 180; % The tilt of the grating in radians.

% *** To lengthen the period of the grating, increase pixelsPerPeriod.
pixelsPerPeriod = 33; % How many pixels will each period/cycle occupy?
spatialFrequency = 1 / pixelsPerPeriod; % How many periods/cycles are there in a pixel?
radiansPerPixel = spatialFrequency * (2 * pi); % = (periods per pixel) * (2 pi radians per period)

% *** To enlarge the gaussian mask, increase periodsCoveredByOneStandardDeviation.
% The parameter "periodsCoveredByOneStandardDeviation" is approximately
% equal to
% the number of periods/cycles covered by one standard deviation of the radius of
% the gaussian mask.
periodsCoveredByOneStandardDeviation = 1.5;
% The parameter "gaussianSpaceConstant" is approximately equal to the
% number of pixels covered by one standard deviation of the radius of
% the gaussian mask.
gaussianSpaceConstant = periodsCoveredByOneStandardDeviation  * pixelsPerPeriod;

% *** If the grating is clipped on the sides, increase widthOfGrid.
widthOfGrid = 400;
halfWidthOfGrid = widthOfGrid / 2;
widthArray = (-halfWidthOfGrid) : halfWidthOfGrid;  % widthArray is used in creating the meshgrid.


% For an explanation of the try-catch block, see the section "Error Handling"
% at the end of this document.
try
    
	% ---------- Window Setup ----------
	% Opens a window.

	% Screen is able to do a lot of configuration and performance checks on
	% open, and will print out a fair amount of detailed information when
	% it does.  These commands supress that checking behavior and just let
    % the demo go straight into action.  See ScreenTest for an example of
    % how to do detailed checking.
	oldVisualDebugLevel = Screen('Preference', 'VisualDebugLevel', 3);
    oldSupressAllWarnings = Screen('Preference', 'SuppressAllWarnings', 1);
	
    % Find out how many screens and use largest screen number.
    whichScreen = max(Screen('Screens'));
    
	% Hides the mouse cursor
	HideCursor;
	
	% Opens a graphics window on the main monitor (screen 0).  If you have
	% multiple monitors connected to your computer, then you can specify
	% a different monitor by supplying a different number in the second
	% argument to OpenWindow, e.g. Screen('OpenWindow', 2).
	window = Screen('OpenWindow', whichScreen);

	  
	% ---------- Color Setup ----------
	% Gets color values.

	% Retrieves color codes for black and white and gray.
	black = BlackIndex(window);  % Retrieves the CLUT color code for black.
	white = WhiteIndex(window);  % Retrieves the CLUT color code for white.
	gray = (black + white) / 2;  % Computes the CLUT color code for gray.
	if round(gray)==white
		gray=black;
    end
	 
	% Taking the absolute value of the difference between white and gray will
	% help keep the grating consistent regardless of whether the CLUT color
	% code for white is less or greater than the CLUT color code for black.
	absoluteDifferenceBetweenWhiteAndGray = abs(white - gray);


	% ---------- Image Setup ----------
	% Stores the image in a two dimensional matrix.

	% Creates a two-dimensional square grid.  For each element i = i(x0, y0) of
	% the grid, x = x(x0, y0) corresponds to the x-coordinate of element "i"
	% and y = y(x0, y0) corresponds to the y-coordinate of element "i"
	[x y] = meshgrid(widthArray, widthArray);
    
    % Replaced original method of changing the orientation of the grating
    % (gradient = y - tan(tiltInRadians) .* x) with sine and cosine (adapted from DriftDemo). 
    % Use of tangent was breakable because it is undefined for theta near pi/2 and the period
    % of the grating changed with change in theta.  

    a=cos(tiltInRadians)*radiansPerPixel;
	b=sin(tiltInRadians)*radiansPerPixel;
	 
	% Converts meshgrid into a sinusoidal grating, where elements
	% along a line with angle theta have the same value and where the
	% period of the sinusoid is equal to "pixelsPerPeriod" pixels.
	% Note that each entry of gratingMatrix varies between minus one and
	% one; -1 <= gratingMatrix(x0, y0)  <= 1
    gratingMatrix = sin(a*x+b*y);
    
	 
	% Creates a circular Gaussian mask centered at the origin, where the number
	% of pixels covered by one standard deviation of the radius is
	% approximately equal to "gaussianSpaceConstant."
	% For more information on circular and elliptical Gaussian distributions, please see
	% http://mathworld.wolfram.com/GaussianFunction.html
	% Note that since each entry of circularGaussianMaskMatrix is "e"
	% raised to a negative exponent, each entry of
	% circularGaussianMaskMatrix is one over "e" raised to a positive
	% exponent, which is always between zero and one;
	% 0 < circularGaussianMaskMatrix(x0, y0) <= 1
	circularGaussianMaskMatrix = exp(-((x .^ 2) + (y .^ 2)) / (gaussianSpaceConstant ^ 2));
	 
	% Since each entry of gratingMatrix varies between minus one and one and each entry of
	% circularGaussianMaskMatrix vary between zero and one, each entry of
	% imageMatrix varies between minus one and one.
	% -1 <= imageMatrix(x0, y0) <= 1
	imageMatrix = gratingMatrix .* circularGaussianMaskMatrix;
	 
	% Since each entry of imageMatrix is a fraction between minus one and
	% one, multiplying imageMatrix by absoluteDifferenceBetweenWhiteAndGray
	% and adding the gray CLUT color code baseline
	% converts each entry of imageMatrix into a shade of gray:
	% if an entry of "m" is minus one, then the corresponding pixel is black;
	% if an entry of "m" is zero, then the corresponding pixel is gray;
	% if an entry of "m" is one, then the corresponding pixel is white.
	grayscaleImageMatrix = gray + absoluteDifferenceBetweenWhiteAndGray * imageMatrix;
	 

	% ---------- Image Display ---------- 
	% Displays the image in the window.
	 
	% Colors the entire window gray.
	Screen('FillRect', window, gray);

	% Writes the image to the window.
	Screen('PutImage', window, grayscaleImageMatrix);

	% Writes text to the window.
	currentTextRow = 0;
	Screen('DrawText', window, sprintf('black = %d, white = %d', black, white), 0, currentTextRow, black);
	currentTextRow = currentTextRow + 20;
	Screen('DrawText', window, 'Press any key to exit.', 0, currentTextRow, black);

	% Updates the screen to reflect our changes to the window.
	Screen('Flip', window);

	% Waits for the user to press a key.
	KbWait;

	% ---------- Window Cleanup ---------- 

	% Closes all windows.
	Screen('CloseAll');
	 
	% Restores the mouse cursor.
	ShowCursor;

    % Restore preferences
    Screen('Preference', 'VisualDebugLevel', oldVisualDebugLevel);
    Screen('Preference', 'SuppressAllWarnings', oldSupressAllWarnings);
catch
   
	% ---------- Error Handling ---------- 
	% If there is an error in our code, we will end up here.

	% The try-catch block ensures that Screen will restore the display and return us
	% to the MATLAB prompt even if there is an error in our code.  Without this try-catch
	% block, Screen could still have control of the display when MATLAB throws an error, in
	% which case the user will not see the MATLAB prompt.
	Screen('CloseAll');

	% Restores the mouse cursor.
	ShowCursor;
    
    % Restore preferences
    Screen('Preference', 'VisualDebugLevel', oldVisualDebugLevel);
    Screen('Preference', 'SuppressAllWarnings', oldSupressAllWarnings);

	% We throw the error again so the user sees the error description.
	psychrethrow(psychlasterror);
    
end