understanding rects/coordinates in psychtoolbox

Hello,

I am trying to write a program that seperates my screen into four quadrants. A circle will randomly appear at the center of each quadrant and the participant must press the spacebar once it appears.

However, I am unsure how to create four rects that are centered at each quadrant. Could anyone provide some knowledge on how I could calculate coordinates/rects. Thank you so much. Much appreciated.

Answer 1

[Abhinav Aravindan]

Hi Jaymie,

To create a program where circles randomly appear in each quadrant and move to a different quadrant when the "Spacebar" is pressed, you can utilize Figure Callbacks in MATLAB. Below is a sample program to help you get started:

function continuous_random_quadrant_circle_on_space() 
figWidth = 800;  
figHeight = 600; 

% Calculate centers of each quadrant within the fixed size 
centers = [ 
    figWidth/4, figHeight/4;        % Quadrant 1 
    3*figWidth/4, figHeight/4;      % Quadrant 2 
    figWidth/4, 3*figHeight/4;      % Quadrant 3 
    3*figWidth/4, 3*figHeight/4     % Quadrant 4 
    ]; 
radius = 50; % Adjust as needed 

% Create a figure window 
fig = figure('Position', [100, 100, figWidth, figHeight]); % Set figure size 
set(fig, 'Color', [1 1 1]); % Set background color to white 
axis equal; 
axis([0 figWidth 0 figHeight]); 
set(gca, 'YDir', 'reverse'); % Reverse y-axis to match screen coordinates 
set(gca, 'XTick', [], 'YTick', []); % Remove axis ticks 

% Set the callback 
set(fig, 'WindowKeyPressFcn', @keyPressCallback); 
disp('Press the spacebar to move the circle. Press "E" to exit.'); 

% Initial display 
updateCircle(); 

% Function to update circle position 
    function updateCircle() 
        if ishandle(fig) 
            % Randomly select one of the quadrant centers 
            idx = randi(4); 
            centerX = centers(idx, 1); 
            centerY = centers(idx, 2); 
            
            clf; 
            hold on; 
            axis equal; 
            axis([0 figWidth 0 figHeight]); 
            set(gca, 'YDir', 'reverse'); 
            set(gca, 'XTick', [], 'YTick', []); 
            set(fig, 'Color', [1 1 1]); 
            
            % Display the circle at the randomly selected quadrant center 
            rectangle('Position', [centerX-radius, centerY-radius, 2*radius, 2*radius], ... 
                'Curvature', [1, 1], 'FaceColor', 'r'); 
            disp(['Circle moved to Quadrant ', num2str(idx)]); 
        end 
    end 

% Callback function to handle key presses 
    function keyPressCallback(~, event) 
        if strcmp(event.Key, 'space') 
            updateCircle();  
        elseif strcmp(event.Key, 'e') 
            disp('Exiting program...'); 
            if ishandle(fig) 
                close(fig);  
            end 
        end 
    end 
end 

Output:

Please find the related documentation below for more detail:

https://www.mathworks.com/help/matlab/creating_plots/create-callbacks-for-graphics-objects.html

https://www.mathworks.com/help/matlab/ref/matlab.ui.figure-properties.html