MATLAB: Crosshairs or just vertical line across linked axis plots

fullcrosshairgraphicshandle graphics

What I have are plots that are linked by the linkaxes() function. I would like to have a vertical line that spans all of the plots so that I can compare the peaks and valleys interactively between plots.

Best Answer

This may get you started:
function vertical_cursors
set(gcf, ...
   'WindowButtonDownFcn', @clickFcn, ...
   'WindowButtonUpFcn', @unclickFcn);
% Set up cursor text
allLines = findobj(gcf, 'type', 'line');
hText = nan(1, length(allLines));
for id = 1:length(allLines)
   hText(id) = text(NaN, NaN, '', ...
      'Parent', get(allLines(id), 'Parent'), ...
      'BackgroundColor', 'yellow', ...
      'Color', get(allLines(id), 'Color'));
end
% Set up cursor lines
allAxes = findobj(gcf, 'Type', 'axes');
hCur = nan(1, length(allAxes));
for id = 1:length(allAxes)
   hCur(id) = line([NaN NaN], ylim(allAxes(id)), ...
      'Color', 'black', 'Parent', allAxes(id));
end
     function clickFcn(varargin)
        % Initiate cursor if clicked anywhere but the figure
        if strcmpi(get(gco, 'type'), 'figure')
           set(hCur, 'XData', [NaN NaN]);                % <-- EDIT

           set(hText, 'Position', [NaN NaN]);            % <-- EDIT
        else
           set(gcf, 'WindowButtonMotionFcn', @dragFcn)
           dragFcn()
        end
     end
     function dragFcn(varargin)
        % Get mouse location
        pt = get(gca, 'CurrentPoint');
        % Update cursor line position
        set(hCur, 'XData', [pt(1), pt(1)]);
        % Update cursor text
        for idx = 1:length(allLines)
           xdata = get(allLines(idx), 'XData');
           ydata = get(allLines(idx), 'YData');
           if pt(1) >= xdata(1) && pt(1) <= xdata(end)
              y = interp1(xdata, ydata, pt(1));
              set(hText(idx), 'Position', [pt(1), y], ...
                 'String', sprintf('(%0.2f, %0.2f)', pt(1), y));
           else
              set(hText(idx), 'Position', [NaN NaN]);
           end
        end
     end
     function unclickFcn(varargin)
        set(gcf, 'WindowButtonMotionFcn', '');
     end
end
Save the above function. Here's an example of how to use it:
subplot(221);
plot(rand(10,1));
subplot(222);
plot(rand(10,2));
subplot(223);
plot([rand(10,1), rand(10,1)+1]);
subplot(224);
plot(rand(10,1));
vertical_cursors;
EDIT: As a response to a request, I added the ability to make the cursor disappear when clicking outside the axes. See the two lines of code with the comment "<-- EDIT".
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