Trouble with custom data tip function (event)

I am puzzled? I try to have a line drawn during the call to a custom text data tip function.

Here is the "normal" response, when clicking on a point with the mouse :

Here's the error message I get when I try to do the same mouse click while adding a few extra lines of code in the callback (first, a screen capture of the message, followed by the code :

Here is the code :

function txt = displayCoordinates(~, info)

global clickedCIE_L clickedCIE_a clickedCIE_b; % sorry for the globals abuse...

clickedCIE_L = info.Position(3); % 69

clickedCIE_a = info.Position(1); % -56

clickedCIE_b = info.Position(2); % 46

% handle_ligne = line([0 0],[clickedCIE_a clickedCIE_b],[0 0],'color',[0 0 1],'lineWidth',4);

DisplayAngle(clickedCIE_a, clickedCIE_b); <<< --------------------- This statement is causing the error?

Hrad = mod(atan2(clickedCIE_b,clickedCIE_a),2*pi); % 2.4539

hueAngle = Hrad*180/pi; % 140 degrés

chroma = sqrt(clickedCIE_a.^2 + clickedCIE_b.^2); % 72

txt = {sprintf('CIE L: %.0f', info.Position(3)), sprintf('CIE a: %.0f', info.Position(1)), sprintf('CIE b: %.0f', info.Position(2)), sprintf('CIE c : %.0f ', chroma), sprintf('CIE h : %.0f °', hueAngle) };

end

function DisplayAngle(a,b)

global clickedCIE_L clickedCIE_a clickedCIE_b;

a_start = 0;

b_start = 0;

a_end = clickedCIE_a

b_end = clickedCIE_b

% Delete existing marker, if any

if ~isempty(handle_ligne)

delete(handle_ligne);

end

handle_ligne = line([a_start a_end],[b_start b_end],[0 0],'color',[0.2 0.2 0.2],'lineWidth',4);

end

It does not matter whether I put the DisplayAngle function inline of not, I still get the error message.

Would there be any other approaches? All I'm trying to add to the figure is a line depicting the hue angle and chroma, at the bottom.

I'll continue looking around for the error on my own in case I find any solution... And I appreciate your precious help.

Answer 1

[Infinite_king]

Hi Roger Breton,

I understand the you are using custom function to update the data tip text, however this was resulting in the 'unable to update the data tip using custom function' error.

I was able to reproduce the error on my end, and with a few changes to the callback function, I was able to get rid of the error. Make the following changes to the callback function to resolve the error,

• Write all the operations in one single callback function. In this case, instead of calling the 'DisplayAngle' function from the 'displayCoordinates' function, insert the operations directly into the callback function itself. For example, the following function works correctly when used as a custom data tip callback function,

function txt = displayCoordinates(~, info)
    global  clickedCIE_L clickedCIE_a clickedCIE_b; % sorry for the globals abuse...
    clickedCIE_L = info.Position(3); % 69 
    clickedCIE_a = info.Position(1); % -56
    clickedCIE_b = info.Position(2); % 46
    
    % insert the required operations here itself
    handle_ligne = line([0 0],[clickedCIE_a clickedCIE_b],[0 0],'color',[0 0 1],'lineWidth',4); 
    % handle_ligne = DisplayAngle(clickedCIE_a, clickedCIE_b);
       
    Hrad = mod(atan2(clickedCIE_b,clickedCIE_a),2*pi); % 2.4539
    hueAngle = Hrad*180/pi; % 140 degrés
    chroma = sqrt(clickedCIE_a.^2 + clickedCIE_b.^2); % 72
    
    txt = {sprintf('CIE L: %.0f', info.Position(3)), sprintf('CIE a: %.0f', info.Position(1)), sprintf('CIE b: %.0f', info.Position(2)), sprintf('CIE c : %.0f ', chroma), sprintf('CIE h : %.0f °', hueAngle)    };
end

• It seems like you are encountering an issue related to the scope of the 'handle_ligne' variable in your 'DisplayAngle function'. Make sure the variable is accessible outside the function. For example,

function DisplayAngle(a, b)
    global handle_ligne; % making it global
    a_start = 0;
    b_start = 0;
    a_end = a;
    b_end = b;
    
    % Delete existing marker, if any
    if ~isempty(handle_ligne) && isvalid(handle_ligne)
        delete(handle_ligne);
    end
    
    % Define handle_ligne in the global scope
    handle_ligne = line([a_start a_end], [b_start b_end], [0 0], 'color', [0.2 0.2 0.2], 'lineWidth', 4);
end

• Save the 'displayCoordinates.m' file in the location that is on the MATLAB path. Alternatively, you can place this function in the same script file.
• Make sure the 'UpdateFcn' property was set correctly.

dcm = datacursormode;
dcm.Enable = 'on';
dcm.UpdateFcn = @displayCoordinates;

For more information, refer the following MATLAB documentation,

Callbacks for Graphics Objects - https://www.mathworks.com/help/matlab/creating_plots/create-callbacks-for-graphics-objects.html

datacursormode documentation - https://www.mathworks.com/help/matlab/ref/matlab.graphics.shape.internal.datacursormanager.html#mw_63999c29-c6b7-48f7-82c7-93e3d76826b8

Hope this is helpful.