MATLAB: Plot line color

Question

I am trying to run the following function so that I can plot some points connected by a line, but the lines are not displaying in the color I want (white). I tried other colors as well, but the lines still won't show. I don't understand why. Can someone help?

    function draw_constellations

    figure
    hold on
    axis([0,100,0,100])
    grid off
    set(gcf,'color','k')
    set(gca,'color','k')
    axis square
    while 1
        [x,y,button] = ginput(1);
        switch button
            case 1 % left mouse
                p = plot(x,y,'w-*');
            case {'q','Q'} % on keyboard
                break;
        end
    end

Answer 1

It is because x and y you used to plot are scalers. To plot lines, you will need to store all the x and y you get from ginput in vectors and plot the vectors:

[x,y,button] = ginput(1);
switch button
    case 1 % left mouse
        xs = [xs x];
        ys = [ys y];
        p = plot(xs,ys,'w-*');
        % more code to go
end

However, if xs and ys are plotted everytime a new point is entered, you will have lines overlapping. To avoid this, we only plot the first point and update the p.XData and p.YData for new points:

if isempty(p)
    p = plot(x,y,'w-*');
else
    p.XData = xs;
    p.YData = ys;

Full code:

figure
hold on
axis([0,100,0,100])
grid off
set(gcf,'color','k')
set(gca,'color','k')
axis square

xs = [];
ys = [];
p = [];

while 1
    [x,y,button] = ginput(1);
    switch button
        case 1 % left mouse
            xs = [xs x];
            ys = [ys y];
            if isempty(p)
                p = plot(x,y,'w-*');
            else
                p.XData = xs;
                p.YData = ys;
            end
        case {'q','Q'} % on keyboard
            break;
    end
end

Result: