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John
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How to implement a 'speed limit' for GUI button press?

Asked by John
on 19 Apr 2011
Hi, I have a GUI built to flip through slices of large 3D image matrices and adjust visualization parameters. When changing slices with a slider, if the slider is clicked too fast in succession the GUI lags a lot because it is trying to render each intermediate image. I want to add a button press 'speed limit' such that: if slider clicks > 1 && time < threshold, skip displaying the intermediate images and just generate display for the final slider setting, else, refresh the image for each slider click, end
I don't know what functions I could use to implement that, as it's not really a timeout. Schemes I can think of using tic, toc or uiwait would require a second click which may not be coming. Any ideas would be appreciated! Thanks!

  1 Comment

Thanks to all for the suggestions. While Matt's answer works, it forces the user to wait between clicks whereas Paulo's answer allows the user to click at will and provides them with a smoother experience regardless. Also, I found that adding 'drawnow' at the end of the image generation code made that function a lot more responsive, which alone fixed the problem for small to moderately sized data sets.

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3 Answers

Answer by Paulo Silva
on 19 Apr 2011
 Accepted Answer

Use a timer (execution mode 'singleShot') in the slider callback:
  1. Check if the timer is running, if not start it and run the slider code
  2. If the timer is already running ignore all the rest of the slider code

  1 Comment

Good answer.
You could also have the timer disable the slider until it's done.

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Answer by Loginatorist on 19 Apr 2011

Just set the 'enable' property to 'inactive' as the first command of the callback, then as the last command, set the 'enable' property to 'on'.

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Answer by Malcolm Lidierth on 19 Apr 2011

Change the callback mode to to 'cancel' instead of 'queue'. Alternatively, test for multiple calls in the callback using isMultipleCall from the FEX. if isMultipleCall();return;end http://www.mathworks.com/matlabcentral/fileexchange/26027

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Here is an example of how this does not work in 2007b.
uicontrol('style','slider',...
'callback','disp(''1''),sort(rand(1,5e6));disp(''2'')',...
'interrupt','off',...
'busyaction','cancel');
Clicking 3 times fast on the right arrow, we should only see one set of numbers, because the busyaction is set to cancel and the interruptable property is set to off. I see three sets of numbers....
Another reason to use isMultipleCall?
Matt - if you add even a short pause(0.1) in your callback string then the busyaction=cancel does indeed run only once, not 3 times. My hunch is that what happens under the hood is that the callback is actually delegated to a separate thread (maybe EDT delegating to the MT?). This delegation happens so quickly that if you double-click the separate clicks do not in fact overlap, and both callbacks will then get executed one after another. However, when you add a pause, it forces the interpreter to use the original thread (instead of delegating), and in this case the clicks *do* overlap and so the second click is discarded.

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