How to end loop after key is press

Hello everyone,

I am attempting to make it so I can have as many iterations as I want in the for loop. I want to choose when I am done using ginput rather than relying on a preset number ("num" in the code below). This would mean running the loop until I press a key, after which the loop is exited. I have attached an image of the plot.

EDIT: I edited the code posted below to reflect my final script that works. If enter is pressed, ginput will not throw an error, and the loop will be exited. If another key is pressed, the loop will also stop. NOTE that when a different key other than 'ENTER' is used to break from the loop, an additional point will be plotted wherever the cursor is located. I am too lazy to fix this at the moment.

clc;clear;close all
rng default
xq = rand(500,1)*5;
yq = rand(500,1)*5;

f = figure;
j = 1;
plot(xq,yq,'b+'); hold on;
axis equal
while true
    try % ginput(number) throws error when 'ENTER' is pressed
        [xv(j), yv(j)] = ginput(1);
        plot(xv(j),yv(j),'ro','MarkerFaceColor','r','MarkerSize',3)
        if j > 1
            plot(xv(j-1:j),yv(j-1:j),'LineWidth',2,'color','red') % polygon
        end
        j=j+1;
    catch
        break;
    end
    
    % In case something other than enter is pressed
    if f.CurrentCharacter > 0
        break;
    end
end

in = inpolygon(xq,yq,xv,yv);
figure
plot(xv,yv,'LineWidth',2,'color','red') % polygon
axis equal
hold on
plot(xq(in),yq(in),'r+') % points inside
plot(xq(~in),yq(~in),'bo') % points outside

Answer 1

[Scott MacKenzie]

Here's an arrangement I've used with good success in the past. The loop executes indefinitely until a key is pressed.

f = figure;
% other code
while true
    
    % put your loop code here
    
    if f.CurrentCharacter > 0
        break;
    end

end

[Addison Collins]

Scott, I modified my code to include yours.

I get the following error when I press a key. I think ginput doesn't like it much. I don't know much about adding exceptions to errors, is there anything I can do? I am able to plot as many points as I want, the issue only arrises when I press a key to exit the loop.

Figure: plotting several points

Error: when I attempt to leave via key press (ginput causes issues)

clc;clear;close all
rng default
xq = rand(500,1)*5;
yq = rand(500,1)*5;

f = figure;
j = 1;
plot(xq,yq,'b+'); hold on;
axis equal

while true
%     [xv(j,1), yv(j,1)] = ginput(1);
    [xv(j), yv(j)] = ginput(1);
    plot(xv(j),yv(j),'ro','MarkerFaceColor','r','MarkerSize',3)
    if j > 1
        plot(xv(j-1:j),yv(j-1:j),'LineWidth',2,'color','red') % polygon
    end
    j=j+1;
    
    if f.CurrentCharacter > 0
        break;
    end
end
in = inpolygon(xq,yq,xv,yv);
figure
plot(xv,yv,'LineWidth',2,'color','red') % polygon
axis equal
hold on
plot(xq(in),yq(in),'r+') % points inside
plot(xq(~in),yq(~in),'bo') % points outside
hold off

[Scott MacKenzie]

Hmm, OK. Actually, I didn't even look at your code. I was just thinking "exit a loop when a key is pressed". Try this (instead of the code in my answer). Hit 'q' when you want to exit the loop.

while true   
    
    ...
        
    [xv(j), yv(j), key] = ginput(1);   
    if key == 'q'
        break;
    end
    
end

[Addison Collins]

I found that adding a pause gives me a time window to press a key without ginput freaking out. But it's not optimal to use this in my code because if I miss the timing, the program crashes due to the error...

while true
%     [xv(j,1), yv(j,1)] = ginput(1);
    [xv(j), yv(j)] = ginput(1);
    plot(xv(j),yv(j),'ro','MarkerFaceColor','r','MarkerSize',3)
    if j > 1
        plot(xv(j-1:j),yv(j-1:j),'LineWidth',2,'color','red') % polygon
    end
    j=j+1;
    
    if f.CurrentCharacter > 0
        break;
    end
    pause(.3) %THIS IS THE PAUSE 
end

[Scott MacKenzie]

I've deleted this comment, as I see in your next comment that you've now got things working just fine.

[Addison Collins]

I realized that ginput just doesn't like 'ENTER'. It attempts to return an invalid 0x0 or something along those lines. Instead, if I press any other key, it works (spacebar, etc.). Additionally, I added a catch so if enter is pressed it will break rather than throw an error.

I will edit my orignal post for anyone who sees this thread in the future.

clc;clear;close all
rng default
xq = rand(500,1)*5;
yq = rand(500,1)*5;

f = figure;
j = 1;
plot(xq,yq,'b+'); hold on;
axis equal
while true
    try % ginput(number) throws error when 'ENTER' is pressed
        [xv(j), yv(j)] = ginput(1);
        plot(xv(j),yv(j),'ro','MarkerFaceColor','r','MarkerSize',3)
        if j > 1
            plot(xv(j-1:j),yv(j-1:j),'LineWidth',2,'color','red') % polygon
        end
        j=j+1;
    catch
        break;
    end
    
    % In case something other than enter is pressed
    if f.CurrentCharacter > 0
        break;
    end
end

in = inpolygon(xq,yq,xv,yv);
figure
plot(xv,yv,'LineWidth',2,'color','red') % polygon
axis equal
hold on
plot(xq(in),yq(in),'r+') % points inside
plot(xq(~in),yq(~in),'bo') % points outside