Allow user to draw a line using mouse

How can I get a user to draw a line using their mouse in an App Designer app using R2019a?

Edit: If App Designer does not support it, will GUIDE?

Thanks in advance.

[Ajay Kumar]

Do you mean line on the axes in uifigure?

[John D]

Yes

Answer 1

[Adam Danz]

If you have the image processing toolbox, use drawline(). Something will have to trigger the function such as a button press or context menu selection. The example below responds to a button press which will then allow the user to click-and-drag a single line on an existing UIAxes.

 function ButtonPushed(app, event)
 hold(app.UIAxes, 'on') 
 drawline(app.UIAxes)
 %        ^^^^^^^^^^  your ui axis handle
 end

[John D]

Thanks for the reply.

However, I get the following error:

Error using images.roi.internal.ROI/parseInputs

ROI parent must be a valid Axes object.

Error in images.roi.Line

Error in drawline (line 158)

h = images.roi.Line(varargin{:});

[Adam Danz]

What handle are you providing to drawline()? As the error indicates, it must be a handles to an axis or UIAxis. What version of matlab are you using?

[John D]

I'm using version 2019a

[Adam Danz]

The first question was more important.

[John D]

The handle I am providing is "app.UIAxes" which is the name of an axes control in my app.

I have tried this in MATLAB online and it seems to work, but offline, this error appears.

[Adam Danz]

Maybe it's a version issue. I have r2019a available and can test this in a couple of hours and get back to you.

[John D]

Thanks

[Adam Danz]

John, I confirmed that drawline() was not supported for UIAxes in r2019a. It is supported in r2019b. Unfortunately imline() also isn't supported for uiaxes in r2019a (it uses a context menu which doesn't fly with UIAxes).

Option 1 is to use a newer release of Matlab (lots of changes were made to App Designer between 2019a and 2019b so you'd have multiple benefits.

Option 2 is to try to come up with an alternative solution. Could you describe what the purpose of the line will be? Should it always be horizontal or vertical?

[John D]

Unfortunately, I'm limited to use R2019a.

However, I would like the user to click and drag on the axis to draw a line in a similar way. This would be a straight line drawn in any direction.

Could you suggest a workaround?

Thanks so far for your help.

[Adam Danz]

Hi John, I just toyed around with it for a while. Interactivity with UIAxes in r2019a is really limited. In fact, UIAxes don't even support for callback functions in r2019a. When I tried to add a ButtonDownFcn, an error indicated a lack of support.

Much (if not all) of these features are supported in r2019b. There's probably a creative, albeit messy, solution out there but I've ran out of time for the day.

As a comparison, check out the list of interaction and callback methods available for UIAxes in r2019b

https://www.mathworks.com/help/matlab/ref/matlab.ui.control.uiaxes-properties.html#mw_f31653a9-2154-4067-b9c1-71901b9b7606

vs r2019a

https://www.mathworks.com/help/releases/R2019a/matlab/ref/matlab.ui.control.uiaxes-properties.html

[John D]

Ok, thanks for your help.

Would this functionality be available in GUIDE, out of interest?

[Adam Danz]

I'm not sure which function you're asking about. drawline() should work on regular axes used by guide GUIs.

[John D]

I was asking would the user be able to draw a line with their mouse on an axes in GUIDE, but I've tested it with the same code and it doesn't seem to do anything.

Thank you for your help!

[Image Analyst]

I think drawline() SHOULD work. If it doesn't do anything when the user clicks and drags out a line, then post your code.

And you might want to unaccept the answer until it's solved because many people won't even open your question if they see you've accepted an answer already.

[John D]

I have tried it again in a new app, and have now got it to work in GUIDE.

function pushbutton1_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
drawline(handles.axes1);

[Adam Danz]

Ok, good! If you start using a more recent release you could implement it in app designer, too (r2019b or later).