% Clear the workspace
clear;
sca;

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

% Set numbers generated to be random
rng('shuffle');


%--------------------------------------------------------------------------
%                       Screen initialisation
%--------------------------------------------------------------------------

% Find the screen to use for displaying the stimuli. By using "max" this
% will display on an external monitor if one is connected.
screenid = max(Screen('Screens'));

% Determine the values of black and white
black = BlackIndex(screenid);
white = WhiteIndex(screenid);

% Set up our screen
[window, windowRect] = PsychImaging('OpenWindow', screenid, black, [], 32, 2);

% Get the vertical refresh rate of the monitor
ifi = Screen('GetFlipInterval', window);

% Get the width and height of the window in pixels
[screenXpix, screenYpix] = Screen('WindowSize', window);

% Determine the center of the screen. We will need this later when we draw
% our dots.
[center(1), center(2)] = RectCenter(windowRect);

% Queries the display size in mm as reported by the operating system. Note
% that there are some complexities here. See Screen DisplaySize? for
% information. So always measure your screen size directly. We just use the
% reported value for the purposes of this demo.
[widthMM, heightMM] = Screen('DisplaySize', screenid);

% We assume that the reported screen dimensions are correct and use these
% to size our stimulus.
screenYcm = heightMM / 10;
screenXcm = widthMM / 10;
pixPerCm = mean([screenXpix / screenXcm screenYpix/ screenYcm]);

% Set the blend function so that we get nice antialised edges to the dots
% defining our cyliner
Screen('BlendFunction', window, GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

% Set drawing to maximum priority level
topPriorityLevel = MaxPriority(window);
Priority(topPriorityLevel);


%--------------------------------------------------------------------------
%                   Stimulus information
%--------------------------------------------------------------------------

% Radius of the sphere in cm
sphereRadius = 7;

% Maximum depth in pixels
maxDepthPix = sphereRadius * pixPerCm;

% Surface area of the sphere
sphereSurfArea = 4 * pi * sphereRadius^2;

% Specify the number of dots we want on the sphere
dotDensity = 6;
numDots = round(dotDensity * sphereSurfArea);

% Uniformly distribute the points in spherical space
th = 2 .* pi * rand(1, numDots);
ph = asin(-1 + 2 .* rand(1, numDots));

% Convert the point coordinates into cartesian space: we define things in
% 3D and then just use the X and Y coordinates as we are doing an
% Orthographic projection
[sphereCoordsX, sphereCoordsY, sphereCoordsZ] = sph2cart(th, ph, sphereRadius);

% Finally convert to pixels
sphereCoordsX = sphereCoordsX .* pixPerCm;
sphereCoordsY = sphereCoordsY .* pixPerCm;
sphereCoordsZ = sphereCoordsZ .* pixPerCm;

% Maximum and minimum depth possible: we will use this to scale the size of
% the dots
minMaxDepth = [0 1] * sphereRadius * pixPerCm;

% The dot coordinates: these coordinates are 3D
dotCoordsAll = [sphereCoordsX; sphereCoordsY; sphereCoordsZ];

% Set the dot size in pixels
dotMinSizePixels = 4;
dotMaxSizePixels = 8;

% We will randomly color the dots
dotColors = rand(3, numDots) .* white;

% We will update the stimulus on each frame
waitframes = 1;


%--------------------------------------------------------------------------
%                           Drawing Loop
%--------------------------------------------------------------------------

% Start angle and the angle in degrees that we will rotate per frame
angle = 0;
degPerFrame = 0.3;
rotYmat = roty(degPerFrame);

% Get a flip to sync our timing
vbl = Screen(window, 'Flip');

% Do the rendering
while ~KbCheck

    % This is orthographic projection, so we get only the dots which are in
    % front of the plane of the screen
    behindCue = dotCoordsAll(3, :) >= 0;
    dotCoords = dotCoordsAll(1:2, behindCue == 1);

    % Dot sizes for this frame, we add the min and max size for the
    % rescaling operation and then drop them for rendering
    dotDepths = [dotCoordsAll(3, behindCue == 1) minMaxDepth];
    dotsSizes = rescale(dotDepths, dotMinSizePixels, dotMaxSizePixels);
    dotsSizes = dotsSizes(1:end-2);

    % Colors of the dots that we will display
    theDotColors = dotColors(:, behindCue == 1);

    % Draw the dots
    Screen('DrawDots', window, dotCoords, dotsSizes,...
        theDotColors, [screenXpix / 2 screenYpix / 2], 2);

    % Flip to the screen
    vbl = Screen('Flip', window, vbl + (waitframes - 0.5) * ifi);

    % Increment the angle and rotate the 3D coordinates: there are much
    % more efficient ways in which to do this which are shown in subsequent
    % demos. Here we just do a simple loop so that you can get the
    % numerical values on each frame.
    dotCoordsAll = doRotation(dotCoordsAll, rotYmat, numDots);

end

% Wait for a button press to exit the demo
sca;

% Function to rotate the dots
function dotCoordsAll = doRotation(dotCoordsAll, rotYmat, numDots)

for i = 1:numDots
    dotCoordsAll(:, i) = dotCoordsAll(:, i)' * rotYmat;
end

end

Published with MATLAB® R2022b