Need help modifying a piece of code that allows the user to draw lines

    function draw_lines
  % Click the left mouse button to define a point
  % Drag the mouse to draw a line to the next point and
  % left click again
  % Right click the mouse to stop drawing
  % 
  figure('WindowButtonDownFcn',@wbdcb)
  ah = axes('DrawMode','fast');
  axis ([-10 10 -10 10])

%open the file to save the coordinates into
fileID = fopen('coord.txt','w');

     function wbdcb(src,evnt)

        if strcmp(get(src,'SelectionType'),'normal')       
           [x,y,str] = disp_point(ah);

           %write the coordinates into the file
           A=[x,y];
           fprintf(fileID,'%6.2f %6.2f\n',A);

           hl = line('XData',x,'YData',y,'Marker','.');
           text(x,y,str,'VerticalAlignment','bottom');drawnow
           set(src,'WindowButtonMotionFcn',@wbmcb)

        elseif strcmp(get(src,'SelectionType'),'alt')
           set(src,'WindowButtonMotionFcn','')
           [x,y,str] = disp_point(ah);

           %write the coordinates into the file
           A=[x,y];
           fprintf(fileID,'%6.2f %6.2f\n',A);

           text(x,y,str,'VerticalAlignment','bottom');drawnow
           fclose(fileID);
        end
        function wbmcb(src,evnt)
           [xn,yn,str] = disp_point(ah);
           xdat = [x,xn];
           ydat = [y,yn];
           set(hl,'XData',xdat,'YData',ydat);
        end  
     end
     function [x,y,str] = disp_point(ah)
        cp = get(ah,'CurrentPoint');  
        x = cp(1,1);y = cp(1,2);
        str = ['(',num2str(x,'%0.3g'),', ',num2str(y,'%0.3g'),')'];    
     end
  end

I need to modify this code so that the first line starts from the origin(0,0) and there onwards the user can click on the graph to draw lines. This is a recycled code that I found online so I am not entirely sure how it works. Any help would be much appreciated.

Answer 1

[Purushottama Rao]

If you want to see {0,0} before the mouse click, use this code

function draw_lines
  % Click the left mouse button to define a point
  % Drag the mouse to draw a line to the next point and
  % left click again
  % Right click the mouse to stop drawing
  % 
  clc
  figure('WindowButtonDownFcn',@wbdcb)
  k=1;
  ah = axes('DrawMode','fast');
  axis ([-10 10 -10 10])%open the file to save the coordinates into
fileID = fopen('coord.txt','w');
 hl = line('XData',0,'YData',0,'Marker','.');
 str=['(',num2str(0),num2str(0),')'];
 text(0,0,str,'VerticalAlignment','bottom');drawnow
     function wbdcb(src,evnt)        
         if strcmp(get(src,'SelectionType'),'normal')       
           [x,y,str] = disp_point(ah);           %write the coordinates into the file
           A=[x,y];
           fprintf(fileID,'%6.2f %6.2f\n',A);           hl = line('XData',x,'YData',y,'Marker','.');
           text(x,y,str,'VerticalAlignment','bottom');drawnow
           set(src,'WindowButtonMotionFcn',@wbmcb)        
         elseif strcmp(get(src,'SelectionType'),'alt')
           set(src,'WindowButtonMotionFcn','')
           [x,y,str] = disp_point(ah);           %write the coordinates into the file
           A=[x,y];
           fprintf(fileID,'%6.2f %6.2f\n',A);           text(x,y,str,'VerticalAlignment','bottom');drawnow
           fclose(fileID);
        end
        function wbmcb(src,evnt)
           [xn,yn,str] = disp_point(ah);
           xdat = [x,xn];
           ydat = [y,yn];
           set(hl,'XData',xdat,'YData',ydat);
        end  
     end
     function [x,y,str] = disp_point(ah)
         if k==1
             x=0;y=0;
             k=0; 
         else
        cp = get(ah,'CurrentPoint');  
        x = cp(1,1);y = cp(1,2);
         end
        str = ['(',num2str(x,'%0.3g'),', ',num2str(y,'%0.3g'),')'];    
     end
  end

[Ashfaq Ahamed]

Thanks a lot Purushottama Rao, but this solves just one part of the problem. It displays the origin (0,0) but I want the first click to be at this point as well but without the user having to click on it manually. Any feedback would be much appreciated

Answer 2

[Purushottama Rao]

Assign a flag for the first click and reset it afterwards. Use the flag to set the coordinates to {0,0}. Hope this is what you are looking for

 function draw_lines
    % Click the left mouse button to define a point
    % Drag the mouse to draw a line to the next point and
    % left click again
    % Right click the mouse to stop drawing
    % 
    clc
    figure('WindowButtonDownFcn',@wbdcb)
    k=1; % Flag for origin
    ah = axes('DrawMode','fast');
    axis ([-10 10 -10 10])%open the file to save the coordinates into
  fileID = fopen('coord.txt','w');
       function wbdcb(src,evnt)        
           if strcmp(get(src,'SelectionType'),'normal')       
             [x,y,str] = disp_point(ah);           %write the coordinates into the file
             A=[x,y];
             fprintf(fileID,'%6.2f %6.2f\n',A);           hl = line('XData',x,'YData',y,'Marker','.');
             text(x,y,str,'VerticalAlignment','bottom');drawnow
             set(src,'WindowButtonMotionFcn',@wbmcb)        
           elseif strcmp(get(src,'SelectionType'),'alt')
             set(src,'WindowButtonMotionFcn','')
             [x,y,str] = disp_point(ah);           %write the coordinates into the file
             A=[x,y];
             fprintf(fileID,'%6.2f %6.2f\n',A);           text(x,y,str,'VerticalAlignment','bottom');drawnow
             fclose(fileID);
          end
          function wbmcb(src,evnt)
             [xn,yn,str] = disp_point(ah);
             xdat = [x,xn];
             ydat = [y,yn];
             set(hl,'XData',xdat,'YData',ydat);
          end  
       end
       function [x,y,str] = disp_point(ah)
           if k==1
               x=0;y=0;
               k=0; % Reset the flag for origin
           else
          cp = get(ah,'CurrentPoint');  
          x = cp(1,1);y = cp(1,2);
           end
          str = ['(',num2str(x,'%0.3g'),', ',num2str(y,'%0.3g'),')'];    
       end
    end

if true
  % code
end