MATLAB: How to create mouse movement event on UIAxes in APP Designer to catch cursor location on the axes

Question

I have a UIAxes created in App designer. now I want to show cursor's x y location when mouse is moving on the axe, not click.

Answer 1

Here are 2 methods to capture mouse coordinates within the axes of a figure.

In these demos the coordinates of the cursor's current point on the axes will appear in the text box. When the mouse leaves the axes, the textbox will clear.

Be aware of the limit in precision of CurrentPoint within axes (see this explanation). For example, you may not be able to select an exact coordinate such as (0,0).

Method 1: Use a pointer manager (requires Image Processing Toolbox)

Instead of using the WindowButtonMotionFcn which requires you to detect when the mouse enters the axes, use a pointer manager assigned to the axes that returns the axes' current point when the mouse is over the axes. This is more efficient than the WindowButtonMotionFcn.

Demo attached: showCurrentPointApp.mlapp

Add this to you app's startup function.

Key components

• Uses iptPointManager and iptSetPointerBehavior which respond to the cursor moving in the axes and exiting the axes.
• app.UIAxes - handle to the app's axes
• app.UIFigure - handle to the app's figure
• app.CurrentPositionEditField - handle to the text box
• startupFcn() - the app's startup function (see instructions to add startupFcn).

% Code that executes after component creation
function startupFcn(app)
    pm.enterFcn = [];
    pm.exitFcn  = @(~,~) set(app.CurrentPositionEditField, 'Value', '');
    pm.traverseFcn = @(~,~) set(app.CurrentPositionEditField, 'Value',...
        sprintf('%.2f,  %.2f', app.UIAxes.CurrentPoint(1,1:2)));
    iptSetPointerBehavior(app.UIAxes, pm)
    iptPointerManager(app.UIFigure,'enable');
    set(app.UIFigure,'WindowButtonMotionFcn',@(~,~)NaN) %dummy fcn so that currentpoint is continually updated
end

Method 2: Assign a WindowButtonMotion to the figure

As Mohammad Sami suggested, the WindowButtonMotion function is assigned in AppDesigner > Designer View > in the Component Browser select the figure handle > callback > WindowButtonMotionFcn.

Demo attached: showCurrentPointApp_method2.mlapp

Key components

• app.UIAxes - handle to the app's axes
• app.UIFigure - handle to the app's figure
• app.CurrentPositionEditField - handle to the text box
• UIFigureWindowButtonMotion() - See instructions above.

% Window button motion function: UIFigure
function UIFigureWindowButtonMotion(app, event)
    % Determine if mouse is within uiaxes
    cp = app.UIFigure.CurrentPoint;
    isInAxes = cp(1) >= app.UIAxes.Position(1) && ...
        cp(1) <= sum(app.UIAxes.Position([1,3])) && ...
        cp(2) >= app.UIAxes.Position(2) && ...
        cp(2) <= sum(app.UIAxes.Position([2,4]));
    if isInAxes
        % Update displayed coordinates
        set(app.CurrentPositionEditField, 'Value',...
            sprintf('%.2f,  %.2f', app.UIAxes.CurrentPoint(1,1:2)))
    else
        % Clear displayed coordinates
        set(app.CurrentPositionEditField, 'Value', '')
    end
end