How to display multiple rect frames simultaneously

Programming Help
1

I am using Psychtoolbox R2020a on MacOS and am using this for loop to display 3 rect frames around my stimuli. However, I cannot get them to display.

% Make a base Rect of 200 by 200 pixels
baseRect = [0 0 300 75];

% Pen width for the frames
penWidthPixels = 6;

% Screen X positions of our three rectangles
squareXpos = [leftX rightX upX];
squareYpos = [leftY rightY upY];
numSquares = 3;

% Make our rectangle coordinates
allRects = nan(4, 3);
for i = 1:numSquares
    allRects(:, i) = CenterRectOnPointd(baseRect, squareXpos(i), screenYpos(i));
end

% Display rects to screen
Screen('FrameRect', window, white, allRects, penWidthPixels);
2

Looks ok, do you Screen(‘Flip’) after drawing?

3

I didn’t add it before, but even when I do add it, it does not work. It seems to work if the y-co-ordinate is fixed, such as ‘ycenter’, but not when I change it to squareYpos(i). Will using the index twice affect the for loop?