Using a single slider to update multiple plots in Matlab

Question

I'm writing a script that will create 2 suplots, and have either a single slider that scrolls the x axis of both plots, or 2 sliders that individually control each subplots x axis.

I have been using an adapted version of Steven Lords FileExchange scrolling plot demo for my slider.

Right now it will only update the most recent plot (as it is currently using gca in its callback function). I've tried just replacing gca with the axes I want (the variables first_plot or second_plot) but this doesn't seem to work.

My question is then, how should I adapt this function to either control both plots or each plot individually? Here is an example of the script I am writing:

x=0:1e-2:2*pi;
y=sin(x);
dx=2;
first_plot = subplot(2,1,1);
plot(x, y);
scrollplot(dx, x)
%Plot the respiration and probe data with scrolling bar

second_plot = subplot(2,1,2);
plot(x, y); 
scrollplot(dx,x)

% dx is the width of the axis 'window'
function scrollplot(dx, x)
a=gca;
% Set appropriate axis limits and settings
set(gcf,'doublebuffer','on');

set(a,'xlim',[0 dx]);

% Generate constants for use in uicontrol initialization
pos=get(a,'position');
Newpos=[pos(1) pos(2)-0.1 pos(3) 0.05];
% This will create a slider which is just underneath the axis
% but still leaves room for the axis labels above the slider
xmax=max(x);
%S= set(gca,'xlim',(get(gcbo,'value')+[0 dx]));   
S=['set(gca,''xlim'',get(gcbo,''value'')+[0 ' num2str(dx) '])'];
% Setting up callback string to modify XLim of axis (gca)
% based on the position of the slider (gcbo)

% Creating Uicontrol
h=uicontrol('style','slider',...
    'units','normalized','position',Newpos,...
    'callback',S,'min',0,'max',xmax-dx);
end

Thanks!

Answer 1

You're almost there, but there's some structural issues from when you modified the code from only one set of axes.

The key thing to do is change the callback function from a string to an actual local function. This makes handling the callback much simpler!

I've adapted your code to work with two (or more) axes. Note we only need to set up the scroll bar once! You were setting it up for each axes (the scroll bars were stacked on top of each other) and both scrollers only operated on gca. Just naming the axes isn't enough to change gca, you have to use those variables! I've assigned the axes to an array for easy manipulation.

Please see the comments for details:

x=0:1e-2:2*pi;
y=sin(x);
% dx is the width of the axis 'window'
dx=2;

% Initialise the figure once, and we only need to set the properties once
fig = figure(1); clf;
set( fig, 'doublebuffer', 'on'); 
% Create a placeholder for axes objects
ax = gobjects( 2, 1 );

% Create plots, storing them in the axes object
ax(1) = subplot(2,1,1);
plot(x, y);

ax(2) = subplot(2,1,2);
plot(x, y); 

% Set up the scroller for the array of axes objects in 'ax'
scrollplot( dx, x, ax)

function scrollplot( dx, x, ax )
    % Set appropriate axis limits
    for ii = 1:numel(ax)
        set( ax(ii), 'xlim', [0 dx] );
    end

    % Create Uicontrol slider
    % The callback is another local function, this gives us more
    % flexibility than a character array.
    uicontrol('style','slider',...
        'units', 'normalized', 'position', [0.1 0.01 0.8 0.05],...
        'callback', @(slider, ~) scrollcallback( ax, dx, slider ), ...
        'min', 0, 'max', max(x)-dx );
end

function scrollcallback( ax, dx, slider, varargin )
    % Scroller callback loops through the axes objects and updates the xlim
    val = slider.Value;
    for ii = 1:numel(ax)
        set( ax(ii), 'xlim', val + [0, dx] );
    end
end