Advanced MATLAB: Capture mouse movement

May 27th, 2008

By Doug Hull

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16 Responses to “Advanced MATLAB: Capture mouse movement”

vincent replied on May 31st, 2008 at 21:13 UTC :

hee Doug,

this is a really nice feature… I want to use it for my GUI as well, but if I apply it on real data (obtained from a racecar) then Matlab gives the following error:

Warning: line XData length (2) and YData length (500) must be equal.

and all I did with your m-file was replacing the definition of h into:

h=plot(data(1:500,1),data(1:500,4),’ButtonDownFcn’, @startDragFcn)

and the plot disappears from the figure.
how can I apply this feature to a dataplot?

cheers Vincent

Doug replied on June 2nd, 2008 at 07:41 UTC :

Vincent,

Assign these variables as a trouble shooting step:

x = data(1:500,1)
y = data(1:500,4)

Check to see if these are the same size.

Then try:

plot(x,y) %skip button down for now

Test that

Finally go to this command

plot(x,y,’ButtonDownFcn’, @startDragFcn)

If you take these systematic steps, I think you will find the problem.

Doug

vincent replied on June 4th, 2008 at 18:45 UTC :

yeah I solved that problem, the length of x was not correct. I have it working on my own data, very cool. now i want to put it in my gui, but matlab gave me the following error;

??? Input argument “handles” is undefined.

Error in ==> Data_Postprocessor_v7>startDragFcn at 658
Data=getappdata(handles.figure1,’mydata’)

??? Error while evaluating line ButtonDownFcn

I use the above code at the start in every callback function of the gui to get the data. so it works in all the callback functions but when I put it in the ButtonDown function Matlab produces the above error. is it maybe because a callback function is not the same as the ButtonDown function?

thanks Doug

Vincent

Doug replied on June 5th, 2008 at 08:45 UTC :

Vincent,

I would need to see the code to figure this out. Send it to support and we can figure it out.

www.mathworks.com/support

Jan Lauber replied on June 9th, 2008 at 08:43 UTC :

Very cool. Works great as an intereactive thresholding

Tahim replied on July 1st, 2008 at 16:44 UTC :

I have a similar problem as Vincent. I tried to use these functions inside my GUI, although I think these created functions can’t see the handles of the GUI.
My startDragFcn is written basically the same way as Vincent:

startDragFcn(hObject, eventdata, handles)
%Inside this function handles is not availabel and I need the axes that is stored in the handles.

When I click over the line I get ??? Input argument “handles” is undefined.

Tahim replied on July 1st, 2008 at 17:56 UTC :

I was looking for an answer for this problem in matlab web page and I found the solution. When using the functions presented by the Doug (nice work Doug) all you have to do to use them inside your GUIs is to pass the handles of the GUI inside a cell.

When using additional arguments for the callback function, you must set the value of the property to a cell array (i.e., enclose the function handle and arguments in curly braces). For example,
You can define the callback function to accept additional input arguments by adding them to the function definition. For example,

function startDragFcn(src,eventdata,arg1)

arg1 is an additional argument. In my case I used the handles of the GUI as an additional argument:

function startDragFcn(hObject,eventdata,handles)

So, for the callback function you have to enclose the function handle and the additional arguments in curly braces. For example,

set(hLine,’ButtonDownFcn’,{@startDragFcn,handles});
set(hFigure, ‘WindowButtonUpFcn’,{@stopDragFcn,handles});

Everest replied on July 17th, 2008 at 03:30 UTC :

Hi!
This is really great!:] I’ve used this idea to move the data points on my plot. But here is my query:
the code works really great on Matlab 7.1, but when I run it on the older version (actually it is Matlab 6.1.0.450)
I get the following error:

********************************************************
??? Undefined function or variable ‘f’.

Error in ==> G:\MATLAB_61\MOUSE_CAPTURE\mouse_capt.m (startDragFcn)
On line 66 ==> set(f,’WindowButtonMotionFcn’,@draggingFcn)

??? Error while evaluating line ButtonDownFcn.

??? Undefined function or variable ‘f’.

Error in ==> G:\MATLAB_61\MOUSE_CAPTURE\mouse_capt.m (stopDragFcn)
On line 128 ==> set(f, ‘WindowButtonMotionFcn’,”)

??? Error while evaluating figure WindowButtonUpFcn.
********************************************************

Why is that? What to do to make it work on the older version?

Doug replied on July 18th, 2008 at 12:45 UTC :

Everest,

I just did a quick check. That version of MATLAB is about three years ago. There have been enough changes in function handles that I suspect that is the reason code written for the newer version of MATLAB does not work in an older version.

Doug

Everest replied on July 24th, 2008 at 08:18 UTC :

Thanks Doug!

The problem is solved now.. Actually I’ve used UserData property to gave the name to my ‘figure’,axis’ and ‘line’ so I could call them in the external function (draggingFcn etc.)
However, it was not so obvious at the beginning.

Everest

Örjan Henriksson replied on September 6th, 2009 at 05:52 UTC :

Hello Doug!

Many thanks for your excellent videos, it sure makes it easier for newbies like me to get into Matlab. However, I have a question, or actually a couple of questions…

My goal is to make a surface object and be able to change the surface Zdata by clicking and dragging. I have been looking through the documentation, the net and all books I could find, but I haven’t been able to find anything that explains how to do that, except from this tutorial. Sure the documentation contains some hints, but I need more than that…

So far, I’ve found some examples that comes close on the File Exchange, namely ‘gnurbs’ by Daniel Claxton and ‘moveplot’ by by Brandon Kuczenski/Alex Woo.

One thing I don’t understand is how to translate the axes ‘CurrentPoint’ property to determine which point of the surface is being clicked on.

Also, by looking at the above two examples, I’ve noticed that they copy the data to be manipulated to the axes ‘userdata’ property. Is this necessary, or is there any way to ’set’ individual points of the surface objects Zdata property directly?

I understand you might not be able to give me a full answer, but maybe you know where I can learn some more about this?

Thanks again and keep up the good work!

Ö.H.

Fatih replied on October 28th, 2009 at 14:15 UTC :

Great Work Doug! Thanks!

I have one question about that..

I want to do samething but not only one graph but also two or three subplots. I mean: i have 2-3 graphs in one figure, and i want to apply samethings to my whole graphs.

Here is the screenshot.

http://img21.imageshack.us/i/adszpu.jpg/

It seems work but i can adjust only one line. Another one didn’t move.

If i understand correctly i can expand this up to 10 graphs.

I am working on it but unfortunately i couldn’t handle with it.

If you could help me, i would be appreciated…

Thanks Again!

dhull replied on October 30th, 2009 at 18:08 UTC :

@Fatih,

Good problem. You will just have to make sure that when you set the XData on the original line, you also set it on all the additional lines. You would want to put the callbacks on all the lines so that any of them can move.

Doug

Fatih replied on November 2nd, 2009 at 06:49 UTC :

@Doug,

I forgot to write here but i find a solution to handle it.

http://img682.imageshack.us/i/adszkh.jpg/

If someone need this i can send my program.

Fatih

Lucy replied on November 9th, 2009 at 14:37 UTC :

Hi Doug,

I’m learning how to create GUIs in Matlab and your GUI tutorials have really helped me. I would like to implement the above function for capturing mouse movement into a GUI, but I’m having lots of problems. At the moment I can’t even get the xdata line to appear. Please could you suggest how to go about implementing your code below into GUI form? Any hints would be very,very much appreciated!

************************************************************
function main
axes = handles.axes1
ah = axes(’xlim’,[0 1],’ylim’,[0 1])
h = hLine([0.5 0.5], [0 1],…
‘color’, ‘red’,…
‘linewidth’, 3,…
‘ButtonDownFcn’, @startDragFcn)

set(f, ‘WindowButtonUpFcn’, @stopDragFcn)

function startDragFcn(varargin)
set(f, ‘WindowButtonMotionFcn’,@dragginFcn)

function dragginFcn(varargin)
pt = get(aH, ‘CurrentPoint’)
set(h, ‘xData’, pt(1)*[1 1])

function stopDragFcn(varargin)
set(f, ‘WindowButtonMotionFcn’,”)
************************************************************

Many thanks

Lucy

dhull replied on November 10th, 2009 at 21:09 UTC :

@lucy,

With just this snippet, I can not really tell anything.

My guess is that the handles of the various objects you are using in the callbacks are going out of scope. This is very common for people doing GUIs. Go take a look at my second GUI video (next to oldest in the TOPIC GUI to right).

That might help, though it is not specific to this at all.

Doug

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May 27th, 2008