pause vs drawnow in app designer

Hi folks,

in my current function I used drawnow to update a figure in a while loop. But drawnow seems to slow down the programm (there are lots of topics on this). I know about the drawnow limitrate, but this command doesn't work with Matlab Compiler (figure begins to blink when compiled).

So today i tried to use the pause command instead of drawnow. This seems to speedup the code and the redrawing of the figure but all the interactivity of callbacks get's lost (needs lots of time!!!).

Is there anything else I could try to increase the performance of my code?

[Ameer Hamza]

What about using pause() every n-th (say, n=5) iteration.

Answer 1

[Mario Malic]

I use drawnow in combination with the pause of 0.1s. I did not experiment with the values of pause.

while
    %code
    drawnow
    pause (0.1)
end

They don't get lost, it's just that they get queued because program waits as it has been told.

[Dominik Müller]

The combination of both commands doesn't seem to increase the performance. I already tried this combination. I also tried:

pause(0.005);
drawnow;
pause(0.005);

Or pause first and drawnow second. Didn't make any changes. The only thing increasing performance is pause(0.005) without drawnow but the problem is as in the description above.

[Mario Malic]

No need for the second pause, try increasing it to 0.01, as 0.005 is super low.

[Dominik Müller]

I found out if I plot on UIAxes instead of a seperate figure drawnow limitrate works fine. No blinking of the figure after Compiler. So limitrate is an option which improves the performance. pause() even if it's 10ms isn't changing performance in combination with drawnow.

[Mario Malic]

Figure blinking might be the issue with the focus or when you use uigetfile/uigetfolder etc.

Due to the fact that you had two figures, drawnow might focus one and then the other causing the blink. I am not familiar with the details what that function actually does.

[Mario Malic]

Dominik's comment:

no I only had one figure all the time. But if I plot on a seperate figure instead of an UIAxes the figure blinks if I use drawnow limitrate.

Now I get to another point: Is it possible that drawing on an UIAxes is less efficient than drawing on a common figure?

Updating figure in while loop might be heavy on the resources, can you show example of code you're using within while loop. This might be also useful for your plots refreshdata.

[Dominik Müller]

            h = animatedline(app.UIAxes);
            axis(app.UIAxes,[0,4*pi,-1,1])

            x = linspace(0,4*pi,1000);
            y = sin(x);
            nToc = 0;
            toc_calc = 0;
            for k = 1:length(x)
                tic
                addpoints(h,x(k),y(k));
                drawnow 
                nToc = nToc + 1;
                toc_calc = toc_calc + toc;
            end
            avgTime = toc_calc/nToc;
            app.averagetimeLabel.Text = 'average time: ' + string(avgTime)+ 's';
            

this is a simple example based on the help page for animatedline. If you want to see the difference between them remove 'app.UIAxes' in line 1 and line 2. the for loop is basecally replacing the while loop.

Edit: without app.UIAxes (plotting on common figure) the code runs about 4 times faster than drawing on UIAxes

Edit2: I found the following link which could be interesting:

https://itectec.com/matlab/matlab-matlab-app-designer-drawnow-is-extremely-slow/

Appdesigner (or specifically UIFigure) employs a HTML/Javascript layer which is less efficient than the standard matlab figure.

[Dominik Müller]

I checked the CPU usage of both code versions. The one drawing on UIAxes increases the CPU usage about 20-40% compared to the one drawing on the common figure.

[Bruno Luong]

Instructive. Comparison like this comforts me that I should stay on GUI rather than switch to app Designer

[Mario Malic]

What is purpose of addpoints? The way it is written is similar to plot function which will have same or maybe better performance. drawnow refreshes all figures, even having one is an issue if you would like to have it refreshed dozens of times.

for k = 1:length(x)
    tic
    addpoints(h,x(k),y(k));
    drawnow 
    nToc = nToc + 1;
    toc_calc = toc_calc + toc;
end

There are some examples on animatedline documentation to speed up animation, by adding more than one point at a time and so on.

You can also try by setting the XData and YData properties of UIAxes (not sure if this is possible with animatedline) within the loop by adding the elements together, that way you avoid the plot function, and only use drawnow to refresh data.

Profiler is a neat way to test performance of what you have written, check it here.

[Bruno Luong]

Under the hood of animatedline is perhaps set x, y data with better handling of FIFO graphical data points.

I try to replace with SET, it does not get any visible faster update, and the conclusion is the same, updatinf plot (happens with drawnow is 3-4 time slower on UIAxes than regular axes.

Regardless the conclusion of the test here is that drawing on uiaxes has poor performance. There is nothing end user can do about it.

[Mario Malic]

Actually it's not the uiaxes, it's the issue with uifigure. What exactly with it, I wouldn't know.

fig = figure; % 0.124s
ax = axes(fig);

fig = figure; % 0.152s
ax = uiaxes(fig);

[Bruno Luong]

Confirmed, I cross check,

matlab.graphics.axis.Axes in UIfigure (app designer): slow 0.0303

ax = axes(figure): fast 0.0071

ax = uiaxes(figure): fast 0.0079

Answer 2

[Dominik Müller]

no I only had one figure all the time. But if I plot on a seperate figure instead of an UIAxes the figure blinks if I use drawnow limitrate.

Now I get to another point: Is it possible that drawing on an UIAxes is less efficient than drawing on a common figure?