% Clear the workspace and the screen sca; close all; clear; % Here we call some default settings for setting up Psychtoolbox PsychDefaultSetup(2); % Seed the random number generator. Here we use the an older way to be % compatible with older systems. rng('shuffle') % Get the screen numbers. This gives us a number for each of the screens % attached to our computer. For help see: Screen Screens? screens = Screen('Screens'); % Draw we select the maximum of these numbers. So in a situation where we % have two screens attached to our monitor we will draw to the external % screen. When only one screen is attached to the monitor we will draw to % this. For help see: help max screenNumber = max(screens); % Define black and white (white will be 1 and black 0). % For help see: help WhiteIndex and help BlackIndex white = WhiteIndex(screenNumber); black = BlackIndex(screenNumber); % Open an on screen window and color it black % For help see: Screen OpenWindow? [window, windowRect] = PsychImaging('OpenWindow', screenNumber, black); % Get the size of the on screen window in pixels % For help see: Screen WindowSize? [screenXpixels, screenYpixels] = Screen('WindowSize', window); % Get the centre coordinate of the window in pixels % For help see: help RectCenter [xCenter, yCenter] = RectCenter(windowRect); % Enable alpha blending for anti-aliasing % For help see: Screen BlendFunction? % Also see: Chapter 6 of the OpenGL programming guide Screen('BlendFunction', window, GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); % Use the meshgrid command to create our base dot coordinates. This will % simply be a grid of equally spaced coordinates in the X and Y dimensions, % centered on 0,0 % For help see: help meshgrid dim = 10; [x, y] = meshgrid(-dim:1:dim, -dim:1:dim); % Here we scale the grid so that it is in pixel coordinates. We just scale % it by the screen size so that it will fit. This is simply a % multiplication. Notive the "." before the multiplicaiton sign. This % allows us to multiply each number in the matrix by the scaling value. pixelScale = screenYpixels / (dim * 2 + 2); x = x .* pixelScale; y = y .* pixelScale; % Calculate the number of dots % For help see: help numel numDots = numel(x); % Make the matrix of positions for the dots. This need to be a two row % vector. The top row will be the X coordinate of the dot and the bottom % row the Y coordinate of the dot. Each column represents a single dot. For % help see: help reshape dotPositionMatrix = [reshape(x, 1, numDots); reshape(y, 1, numDots)]; % We can define a center for the dot coordinates to be relaitive to. Here % we set the centre to be the centre of the screen dotCenter = [xCenter yCenter]; % Set the color of our dot to be random i.e. a random number between 0 and % 1 dotColors = rand(3, numDots) .* white; % Set the size of the dots randomly between 10 and 30 pixels dotSizes = rand(1, numDots) .* 20 + 10; % Draw all of our dots to the screen in a single line of code % For help see: Screen DrawDots Screen('DrawDots', window, dotPositionMatrix,... dotSizes, dotColors, dotCenter, 2); % Flip to the screen. This command basically draws all of our previous % commands onto the screen. See later demos in the animation section on more % timing details. And how to demos in this section on how to draw multiple % rects at once. % For help see: Screen Flip? Screen('Flip', window); % Now we have drawn to the screen we wait for a keyboard button press (any % key) to terminate the demo. For help see: help KbStrokeWait KbStrokeWait; % Clear the screen. "sca" is short hand for "Screen CloseAll". This clears % all features related to PTB. Note: we leave the variables in the % workspace so you can have a look at them if you want. % For help see: help sca sca;