How can I use ginput in app designer?

I would like to select a range of points from one particular UIAxes in my app.

I have tried to use ginput ([x,y=ginput]), but the applications prompts an additional empty plot to select the range of points. How can I point an specific UIAxes?

Kind Regards

[Wonsup Lee]

I got success by referring to this answer: https://kr.mathworks.com/matlabcentral/answers/506032-how-do-i-select-a-point-on-matlab-uiaxes-and-then-get-data-for-it

Just use drawpoint function instead of drawrectangle.

One line in callback function or a main code.

[x, y] = selectDataPoints(app, app.figArea);

And, create a function.

function [x, y] = selectDataPoints(~, ax)
    roi = drawpoint(ax);
    x = roi.Position(1);
    y = roi.Position(2);
end

Answer 1

[Adam Danz]

ginput is now supported in AppDesigner starting in r2020b

We still don't have an option to specify the target figure handle in ginput so you have to make the App's figure handle visible so ginput doesn't land on the wrong figure or create a new figure.

The example below is a callback function that responds to a button press and does the following:

1. Test that user is using r2020b or later; if not, throw error.
2. Save current state of the app figure handle visibility.
3. Change the app figure handle visibility so that it's accessible to the callback function.
4. Make app figure current
5. Call ginput
6. Return the original figure handle visibility state.

% Button pushed function: Button
function ButtonPushed(app, event)
    % Check Matlab version, throw error if prior to r2020b
    assert(~verLessThan('Matlab', '9.9'), 'ginput not supported prior to Matlab r2020b.')
    
    % Set up figure handle visibility, run ginput, and return state
    fhv = app.UIFigure.HandleVisibility;        % Current status
    app.UIFigure.HandleVisibility = 'callback'; % Temp change (or, 'on') 
    set(0, 'CurrentFigure', app.UIFigure)       % Make fig current
    
    [x,y,b] = ginput(1);                        % run ginput
    
    app.UIFigure.HandleVisibility = fhv;        % return original state
end

See also

• r2020b release notes
• Display graphics in App Designer (r2020b)
• ginput

[Sang Hyeok Yang]

perfectly worked, it really helped. thanks.

[Jon Lagonigro]

Does anyone know how to specify axes using this method?

I have multiple axes in my app and would like to restrict ginput to just one of them as opposed to the entire figure window. ginput supposedly works on the current axes, but when I try something like

set(app.UIFigure,'CurrentAxes',app.UIAxes)

ginput still pops up over the entire UIFigure window.

[Adam Danz]

>Does anyone know how to specify axes using this method?

That's what my answer explains.

>ginput still pops up over the entire UIFigure window

The coordinate returned is in reference to the current axes but the crosshairs appear over the entire figure. If you click outside of the axes, the coordinate will still be in reference to the axes and the value will be outside of your axes limits. If that bothers you, you can set up your own crosshairs by following the examples below.

• https://www.mathworks.com/matlabcentral/answers/603793-show-mouse-position-in-another-subplot#answer_504046
• https://www.mathworks.com/matlabcentral/answers/509060-live-line-plotting-over-a-surface-mesh-imagesc-plot#answer_419673
• https://www.mathworks.com/matlabcentral/answers/548721-ginput-and-currentpoint-property-do-no-match-real-axes-coordinates#answer_451698

Or you can use a different point-selection method

• https://www.mathworks.com/matlabcentral/answers/622418-how-do-you-mark-and-extract-an-area-from-an-imagesc-figure#answer_521373
• datatips

[Jon Lagonigro]

You're right, I needed to set up my own crosshairs to avoid confusion between multiple axes. An option to keep the crosshairs over just the current axes would be a nice option in the future. Thanks!

[Adam Danz]

I agree. You can create a service request > technical support, to make this suggestion.

Contact Us - MATLAB & Simulink

Answer 2

[Jon Nykiel]

Unfortunately, ginput is not supported within appdesigner. However, as of R2019A, the CurrentPoint property can be used within a WindowButtonDown function to get the coordinates of a button click within UIAxes.

Simple example:

function UIFigureWindowButtonDown(app, event)
            temp = app.UIAxes.CurrentPoint; % Returns 2x3 array of points
            loc = [temp(1,1) temp(1,2)]; % Gets the (x,y) coordinates
end    

[Yuan Su]

Thank you very much.

It helps a lot.

Answer 3

[Richard Saumarez]

I agree about the comments on appDesigner

After a lot of work, and bending one's foot round one's ear, one can write a GUI that has most of the functionality written in Visual stdio or Fortran. But it seems counterintuitive and everything that one would like to do, and would think is being easy, is "not supported".

There is no doubt in my mind that appDesigner needs more functionality if one is going to write an artistic, commercially useful, GUI that is not simply knobs and sliders. Apart from the difficulty in getting the mouse position, one desperately needs to be able to draw on the uppermost layer of the GUI, not in a plot, but in the container itself.

I may be being unfair, and this may be possible, but finding one's way around Matlab documentation, apart from the most basic aspects, is really difficult.

Answer 4

[HM]

I found this thread because I was looking for the same thing. We definitely need a 'ginput' function that works within a UIFigure.

However, I did find a workaround: invoke a new 'normal' matlab figure with 'figure' (e.g. MyFigure = figure;) plot on that figure any plots/graphics that you have plotted on your UIFigure (any relevant graphics that you need on there to be able to click relative to). Note, use the traditional plot() command, rather than the plot(app.UIFigure, ) command. Then use the ginput function with that figure. (e.g. MyPoints = ginput;) then delete the figure, and use the recorded values as desired. (e.g. delete(MyFigure); )

This actually worked well for me, as the 'pop-up' figure is larger than my UIFigure, allowing for more accurate mouse clicking.

Hope that helps. Cheers, Hugh.

Answer 5

[chrisw23]

You can define a ButtonDownFcn callback that delivers 'Hit' event data for axes, which has an IntersectionPoint property. This is also valid for lines, but not for ie. the MainFigure (MouseData event only).

This works fine although the AppDesigner doesn't support callback properties for Axes ( tested with SubPlot with Panel Parent in R2018b ).

app.myAx = subplot(2,1,1,'Parent',app.Panel);  % create plot
app.myAx.ButtonDownFcn = createCallbackFcn(app, @app.getMousePosition, true);

function getMousePosition(app,source,event)
    switch event.EventName
        case 'Hit'
            % Properties: Btn/IntersectionPoint/Src/Evnt
            posData = event.IntersectionPoint; % to be used for calc
        case 'MouseData'
            % Properties: Src/EvntName
    end
end

Hope it helps

Christian

[Rajpal Singh]

Is there any solution for app designer also to get points from multiple line plot.

I want draw a staright child line on parent line by clicking on it.

[Richard Saumarez]

Brilliant!

I've been tearing my hair out trying to solve this.

App designer really need a simple to use mouse position function that isn't as tortuous as this.

Answer 6

[Birdman]

You can't. If you check the documentation of ginput, you will see it can not take a predefined axes as an input argument:

https://www.mathworks.com/help/matlab/ref/ginput.html

There might be custom written functions for that though, you just have to google it.

[Mathias Hell]

That is not true. I was working on a Matlab GUI with GUIDE and used the ginput function to select several points on the predefined axes and it worked perfectly. However, when I use the function in the same way in the Maltab App Designer I encounter the described problem.

function setapointbutton_Callback(hObject, eventdata, handles)
handles = guidata(hObject);
zoom(handles.ax,'off');
pan(handles.ax,'off');

while(1)    
    
    handles.length = length(handles.point_x);
    [handles.point_x(handles.length+1,1) ,handles.point_y(handles.length+1,1)] = ginput(1);

    key = get(gcf,'selectiontype');
    if strcmp(key,'alt')
        handles.point_x(handles.length+1,:) = [];
        handles.point_y(handles.length+1,:) = [];
        break;
    else 

        handles.grafikhandle_points(1, handles.length+1) = plot(handles.point_x(handles.length+1,1),handles.point_y(handles.length+1,1),'bo');
        handles.grafikhandle_points(1, handles.length+1).UIContextMenu = handles.c1;
    end

end

[Walter Roberson]

I just looked at the source code. There is no way to pass a figure or an axes to ginput(). Birdman was correct that there is no way to select which figure or axes that ginput() operates on.

ginput() uses gcf(), which will only find traditional figures. If you have no traditional figure that is active then ginput() will open a new figure. So ginput() can work in GUIDE, but it cannot work on uifigures.

Answer 7

[Vlad Atanasiu]

Here is an illustration of how to simulate ginput with uifigures (App Designer, R2020b).

function uiginput
% Get coordinates of clicked point on image in uifigure and uiaxes.
% Remove datatips by pressing "Escape".

% Create uifigure
fig = uifigure;
fig.WindowKeyPressFcn = @onKeyPress;

% Create uiaxes
ax = uiaxes(fig);
ax.PickableParts = 'visible';
ax.HitTest = 'on';

% Display classic image in uiaxes
I = imread('membrane.png'); % 100 x 86 px
im = imshow(I,'Parent',ax);
im.ButtonDownFcn = @onClickImage;


    % Capture clicks on uiaxes
    function [x, y] = onClickImage(~,~)
        
        % Set the image to allow clicks to pass through it
        im.PickableParts = 'none';
        im.HitTest = 'off';

        % Get coordinates of clicked point from uiaxes
        x = ax.CurrentPoint(1);
        y = ax.CurrentPoint(3);

        % Revert above changes to image properties
        im.PickableParts = 'visible';
        im.HitTest = 'on';
        
        % Compute integer pixel coordinates
        if x < 1
            % Correct a location error of one pixel
            % between axes and image coordinates
            x = 1;
        else
            x = floor(x);
        end
        if y < 1
            y = 1;
        else
            y = ceil(y);
        end

        % Delete previous datatips, if any
        try
            dt = findall(fig,'Type','datatip');
            if ~isempty(dt)
                delete(dt)
            end
        catch
            %
        end
        
        % Display pixel coordinates on datatip
        % (The origin is at the top left of the image)
        message = ['x ',num2str(x),', y ',num2str(y)];
        datatip(im,x,y);
        im.DataTipTemplate.DataTipRows(1).Label = message;
        im.DataTipTemplate.DataTipRows(1).Value = [x,y];
        im.DataTipTemplate.DataTipRows(2).Label = '';
        im.DataTipTemplate.DataTipRows(2).Value = '';
        
    end


    % Capture key presses
    function onKeyPress(~, event)

        % Which kwy was pressed?
        clickType = event.Key;
        
        % remove datatip
        if strcmp(clickType,'escape')
            try
                dt = findall(fig,'Type','datatip');
                if ~isempty(dt)
                    delete(dt)
                end
            catch
                %
            end
        end
        
    end

end

[Adam Danz]

@Vlad Atanasiu, ginput is supported in AppDesigner and UIFigures starting in r2020b (see r2020b release notes)

[Vlad Atanasiu]

Indeed. But the problem is if you wish/need to get the coordinates of a clicked point within an image with the user clicking just once. Fo ginput you need two clicks: once to activate the function and once to specify the point. As far as I known, currently (R2020b) only the figure (uifigure) and the axes (uiaxes) have methods to query the clicked point; images (uiimage) don't. This is problematic, since it is cumbersome, and sometimes very cumbersome, to compute compute clicked points in image coordinates from figure coordinates. So you are left with the only alternative of using the axes, and hence displaying images with the imshow function, wich can be attached to axes, instead of uiimage. This is what the above solution presents.

[Vlad Atanasiu]

An example of a case when you would like to get image coordinates with a single click is the following: in a uifigure right-click a uiimage to open an uicontextmenu in which the coordinates of the clicked point are displayed. The problem was posted here on Matlab Answers.

[Adam Danz]

Thanks for the explanation, Vlad Atanasiu. This isn't really a simulation of ginput, though. If you want to grab manually selected coordinates, you can use datacursormode starting in r2020a (demo) but that's still not supported for uiimage objects, as you've discovered. In that case, you're solution will be useful. I recomment using local functions instead of nested functions and pass the fig, ax, and im variables to onKeyPress as input variables.

"For ginput you need two clicks: once to activate the function and once to specify the point. "

Yes, that's true. The difference is that the ginput outputs are immediately available if the user wants to do something programmatically with them.

"As far as I known, currently (R2020b) only the figure (uifigure) and the axes (uiaxes) have methods to query the clicked point; images (uiimage) don't."

Partially correct. If an axis doesn't exist in the app, ginput will create one and its outputs will be in axis units but you can click anywhere in the figure. One workaround would be to put an invisible axis directly over/under the uiimage and make that axis current prior to calling ginput. The invisible axis HandleVisibility should be set to off and its position should be linked to the uiimage position and its axis limit should be set to the uiimage dimensions. But your alternative has some advantages to that approach.

"This is problematic, since it is cumbersome, and sometimes very cumbersome, to compute compute clicked points in image coordinates from figure coordinates. "

That's not quite correct. ginput returns coordinates in axis units (see documentation).

As you mentioned, you could use imshow in which case, ginput is supported (see the demo below using ginput in uifigure / uiaxes with imshow).

app.UIFigure = uifigure('Name', 'Demo ginput'); 
app.UIAxis = axes(app.UIFigure); 
app.UIFigure.HandleVisibility = 'on';

imshow('cameraman.tif', 'Parent', app.UIAxis);

drawnow
pause(1)

[x,y,b] = ginput(1);  

[Vlad Atanasiu]

> you can use datacursormode starting in r2020a

Yes, I was there too, using datatips, but datatips are not substitutes for contextmenu. In particular the content is editable, which might not be desirable; once you edited it other datatips copy the said content. Implementing clickable links via datatips is also difficult, since when you click the datatip it opens for editing. Moreover, datatip have predefined content which becomes visible when the datatips are activated and there is a visible latency between the display of the initial content and the dynamical content that replaces it.

> That's not quite correct. ginput returns coordinates in axis units (see documentation).

Yes, but what if need to get image coordinates without ginput (= two clicks)? [Which is a topic diverging from the initial question in this thread, so we might want to move the discussion to a new thread.]

A fundamental problem is that of Matlab transitioning from Java to JavaScript-based interfaces and a doubling of functions with partially overlapping capabilities and incompatibilies.

[Vlad Atanasiu]

Here is another use case involving getting image coordinates. You display a set of images as imtile, then click on one of them to popup a tooltip with metadata, such as label, then click on the tooltip to display the single image.

I didn't find any satisfactory solution, so I abandoned imtile. Instead I displayed uiimages in uigridlayout, with the metadata in the Tooltip property and the hyperlinks in the ImageClickedFcn callback. I still have the minor visual issue that gaps appear between rows or columns because the gridlayout manager adapts to the aspect ratio of its parent container.

[This comment is also veering towards off-topic, but it explains the wider context of different solutions.]