Psychtoolbox DrawText causes so many missed flips (Matlab)

Question

I am having timing issues with my experiment, I am trying to implement an SSVEP speller with flashing boxes. At each frame I implement the following code that creates the rectangle with the specified color and I use to "DrawText" to indicate the text of letters. However, when I do so, the number of missed flips is very high (above 90%), when I removed all text drawing the performance is normal and very good (around 1%).

I am using window 7 64 bits, with Matlab 2017b, Psychtoolbox-3, I have installed Gstreamer.

My question is how can I correctly display text without performance issues? I tried both DrawText and DrawFormattedText but there is no change. I tried to save the letters into a texture and load the texture but I am not sure how to display the text and draw boxes on top of it with both of them appearing.

Thanks a lot.

function all_rects = create_rects(char_struct,window,drawing_colors,drawing_color_index,black,cue,text_texture)
penWidthPixels = 2;

Screen('TextFont', window, 'Courier New');
Screen('TextSize', window, 15);


num_targets = length(char_struct);
all_rects = nan(4,num_targets);
for i=1:num_targets
    baseRect = [0 0 char_struct(i).size(1) char_struct(i).size(2)];
    all_rects(:,i) = CenterRectOnPointd(baseRect, char_struct(i).x_location, char_struct(i).y_location);      
    Screen('FillRect',window,reshape(drawing_colors(drawing_color_index(i)+1,:),[1,3]),all_rects(:,i));
    if length(char_struct(i).text) > 1 && ~strcmp(char_struct(i).text,'SPACE')
         Screen('DrawText',window, char_struct(i).text,char_struct(i).x_location-15, char_struct(i).y_location+3,0, 100)
    elseif strcmp(char_struct(i).text,'SPACE')
         Screen('DrawText',window,char_struct(i).text,char_struct(i).x_location-40,char_struct(i).y_location+3,0,100);
    else
        Screen('DrawText',window, char_struct(i).text,char_struct(i).x_location-5, char_struct(i).y_location+3,0, 100);
    end
end

Screen('FrameRect', window, black, all_rects,penWidthPixels);
if cue ~=0
    Screen('FrameRect', window, [255 0 0], all_rects(:,cue),penWidthPixels);
end

Screen('DrawingFinished', window);

The flipping is implemented in the main loop with:

vbl = Screen('Flip', window,vbl + 0.5 * ifi);

score 0 · Answer 1 · answered May 22 '18 at 15:28

As you noted, pre-computing the text (either the text itself, or the entire window) as a texture will save resources during your presentation loop. You can draw boxes on top of the texture in the same manner as other Psychtoolbox drawing functions, simply overlay the two prior to flipping the screen:

Screen('DrawTexture', window, text_texture);
Screen('FrameRect', window, black, all_rects, penWidthPixels);
Screen('Flip', window);

Psychtoolbox DrawText causes so many missed flips (Matlab)

1 Answers1