Animated data-tip or xline?

Hello,

I am looking to create an animation of a datatip or a vertical line moving across a plot which has arleady been made. I need to be able to control the framerate of the animation (or, the rate at which the line/datatip moves from one x-value to the next). I then (ideally) need to be able to export this animation as a movie. I've checked the documentation for this and it does not seem intuitive at all. If anyone could provide any assistance, it would be much appreciated!

Here is my attempt so far at making a vertical line move across a simple plot at a rate of 4 frames/second:

x=[1:20]
y=sin(x)

L = xline(0)
a=tic
for i = 1:length(x)
    delete(L)
    L = xline(i)
    b = toc(a)
    if b>1/4
        drawnow
        a=tic
    end
end

As you probably guessed, it does not work as intended at all. The example code I drew from is here, under "control animation speed."

Any help is much appreciated!

Answer 1

[Steven Lord]

Rather than deleting and recreating the line, just update its properties.

x = 0:360;
y = sind(x);
plot(x, y);
h = xline(x(1));
for k = 2:numel(x)
    h.Value = x(k);
    pause(0.25);
end

For a few more bells and whistles and to speed it up a little:

x = 0:360;
y = sind(x);
% Only show one marker, at the x value where the xline is located
s = plot(x, y, 'o-', 'MarkerIndices', 1);
h = xline(x(1));
% Use the title to show where the xline is located
t = title("Sine curve with xline at x = " + x(1));
for k = 2:numel(x)
    h.Value = x(k);
    % 'move' the marker along the sine curve
    s.MarkerIndices = k;
    % Update the title string
    t.String = "Sine curve with xline at x = " + x(k);
    % Let's go a little faster
    pause(1/36);
end

[David Gordon]

Thanks so much this works perfectly! I actually needed to use it on a saved figure with nothing in the workspace, so I just used the first code and set x = [start:end] and it worked like a charm! Thanks again.

[David Gordon]

To take it one step further, any idea how I could save this video as a movie? I've tried messing with the following, but the video doesn't render at all:

v = VideoWriter('274-305.avi');
open(v);

x = [274:305]
h = xline(x(1));
for k = 2:numel(x)
    h.Value = x(k);
    pause(0.5);
    frame=getframe(gcf);
end
writeVideo(v,frame);

[Steven Lord]

Write the frame to the video inside the loop rather than after, as shown in the "Create AVI File from Animation" example on the documentation page for writeVideo.

You probably don't need the pause inside the loop if you set the FrameRate property of the VideoWriter first. Instead you might want to use drawnow instead to make sure MATLAB updates the graphic.