function handles

hei guys,i have a problem with function usage and i kinda get confused with it .my function works when i change the position of the polygon (created with impoly), and it will automatically call the second function that make a new patch that fill the polygon new position. the problem is when i change the position of the polygon, the function keeps on making new patches. is there a way to fill colors while we change the polygon's position?

here is the script that i've wrote

function polygon
axis([0 100 0 100])
h = impoly(gca,[10 10 ; 20 10; 20 20 ; 10 20]);
api = iptgetapi(h);
current_body_coordinates = api.getPosition();
patches(current_body_coordinates)
api.addNewPositionCallback(@patches);

function patches(p)
patches=patch(p(:,1),p(:,2),'r');

thanks in advance :D

Answer 1

[Pratyush Swain]

Hi Mallory,

The problem arises because each time the polygon's position changes, a new patch is created without removing the previous one.

We can update the position of the patch instead of creating a new patch each time:

function polygon
    axis([0 100 0 100])
    
    % Create the polygon
    h = impoly(gca,[10 10 ; 20 10; 20 20 ; 10 20]);
    api = iptgetapi(h);
    current_body_coordinates = api.getPosition();
    
    %  Create a patch using the initial position
    poly_patch = patch(current_body_coordinates(:,1), current_body_coordinates(:,2), 'r');
    
    % Callback to update the patch
    api.addNewPositionCallback(@update_patch);
    
    % Function to update patch
    function update_patch(p)
        set(poly_patch, 'XData', p(:,1), 'YData', p(:,2));
    end
end

For more information on 'patch' function, you can refer to - https://www.mathworks.com/help/matlab/ref/patch.html

Hope this helps.