'"drawnow" function makes working slow.

I'm using timer in app designer.

Between timer operation, I'm using drawnow for instant plotting.

Up to 2020b version, it has been working fine.

But, in 2021a, I have the issue of hagning or very slow update issue.

When I remove the drawnow, it looks working fine.

Is there any better method without revmoving "drawnow"?

Also, can you explain why it is only happened in 2021a?

I already tried "drawnow limitrate". But, it is same.

% timer 
app.updateTimer=timer('BusyMode', 'drop', 'ExecutionMode','fixedSpacing','Period', 0.01,'TimerFcn',@(~,~)app.updateTimerISR);

% it is called during timer
function plot_refresh(app)
g=app.graph_main;
cla(g);
switch app.disp
    case 1
        switch app.x_axis_unit
            case 1
                plot(g,app.data.x_bin,app.data.y);
            case 2
                plot(g,app.data.x_cf,app.data.y);
        end
    case 0
        switch app.x_axis_unit
            case 1
                x=app.data.x_bin;
            case 2
                x=app.data.x_cf;
        end
        y=((-app.es_wbch_hw.num_cap+1):0)';
        s=pcolor(g,x,y,app.data.y_cap);
        s.EdgeColor='none';
end
drawnow();
end

[KSSV]

You try with set command.

[Suk Bum Lee]

How can I use 'set' command in above codes?

Could you elaborate in detail?

Answer 1

[Vinayak]

Hi Suk,

I understand you were facing performance issues with “drawnow”. If you are still facing similar issues in latest MATLAB releases, you might want to consider updating the data of your plot rather than redrawing them entirely. This can be done by using the “set” command (as suggested by KSSV) to modify the properties of your existing plot objects. Here's how you can optimize your “plot_refresh” function:

First, when you create your initial plot, store a handle to it:

app.plotHandle = plot(g, app.data.x_bin, app.data.y); 

Then, during your timer callback, you can update the plot data using the stored handle:

set(app.plotHandle, 'XData', app.data.x_bin, 'YData', app.data.y); 

This approach updates the plot without the overhead of redrawing everything, which should improve the responsiveness of your application. Remember to use “drawnow” or “drawnow limitrate” as needed after updating the plot to ensure the display is refreshed.

I hope this helps.