How do I end a function that is using callbacks in Matlab? - matlab

Question

I am trying to write some code that allow me to 'drag and drop' some lines over a figure so that I can obtain a particular coordinate: 'pt'. I am adapting some code from the internet that uses call backs, which is doing what I want it to do. However, I am unable to end the function or transfer the coordinate 'pt' to another function. I have attempted to use 'return', but it doesn't seem to work. I also tried to use 'while', but it caused Matlab to crash.
I am new to programming, so detailed suggestions would be appreciated.
function [pt] = movelines
global pt;
f=figure;
aH=axes('Xlim',[0, 1],'YLim', [0 1]);
key=0;
H=line([0 1], [0.5 0.5], ... %from [x1 x2] to [y1 y2]
'color', 'yellow',...
'linewidth', 3);
V=line([0.5 0.5], [0 1], ... %This line sets the length of the line. From [x1 x2] to [y1 y2]
'color', 'red', ...
'linewidth',3,...
'ButtonDownFcn', #startDragFcn);
set(f, 'WindowButtonUpFcn',#stopDragFcn);
mov_cancel = uicontrol(f,'Style','pushbutton',...
'Position',[30,130,110,30],...
'String','(cancel)',...
'BusyAction','cancel',...
'TooltipString','BusyAction = cancel',...
'Callback',#funct_cancel);
function startDragFcn (gcbo,eventdata,handles)
set(f,'WindowButtonMotionFcn',#draggingFcn)
end
function draggingFcn (gcbo,eventdata,handles)
pt=get(aH,'CurrentPoint');
set(V,'Xdata',pt(1)*[1 1]);
set(H,'Ydata',pt(1,2)*[1 1])
end
function stopDragFcn (gcbo,eventdata,handles)
set(f,'WindowButtonMotionFcn','');
end
function funct_cancel (gcbo,eventdata,handles)
key=key+1
return
end
end
To use the code, click and hold the vertical line. The function is supposed to end when the cancel button is clicked.

Answer 1

You can use the Matlab function waitfor to wait for a uicontrol object to close. I've also added functionality to stop allowing the user to drag the lines around after you cancel.
function [pt] = movelines()
f=figure;
enabled = 1;
aH=axes('Xlim',[0, 1],'YLim', [0 1]);
key=0;
H=line([0 1], [0.5 0.5], ... %from [x1 x2] to [y1 y2]
'color', 'yellow',...
'linewidth', 3);
V=line([0.5 0.5], [0 1], ... %This line sets the length of the line. From [x1 x2] to [y1 y2]
'color', 'red', ...
'linewidth',3,...
'ButtonDownFcn', #startDragFcn);
set(f, 'WindowButtonUpFcn',#stopDragFcn);
mov_cancel = uicontrol(f,'Style','pushbutton',...
'Position',[30,130,110,30],...
'String','(cancel)',...
'BusyAction','cancel',...
'TooltipString','BusyAction = cancel',...
'Callback',#funct_cancel);
function startDragFcn (gcbo,eventdata,handles)
if enabled
set(f,'WindowButtonMotionFcn',#draggingFcn)
end
end
function draggingFcn (gcbo,eventdata,handles)
pt=get(aH,'CurrentPoint');
set(V,'Xdata',pt(1)*[1 1]);
set(H,'Ydata',pt(1,2)*[1 1])
end
function stopDragFcn (gcbo,eventdata,handles)
set(f,'WindowButtonMotionFcn','');
end
function funct_cancel (gcbo,eventdata,handles)
key=key+1
enabled=0;
delete(mov_cancel);
end
waitfor(mov_cancel);
end

Answer 2

So I assume there is a reason that you aren't using ginput. If you haven't considered it then you should, see: http://uk.mathworks.com/help/matlab/ref/ginput.html
So assuming you want to proceed with your current approach:
Your code at the moment seems to terminate fine, do you mean that you want to close the figure. If so you can do this using delete(gcf) within your callback function.
In terms of returning the current point you could declare pt as a global variable. You can then use it anywhere you want. Remember to declare a global variable at the beginning of each function you use it in.
function draggingFcn (gcbo,eventdata,handles)
global pt;
pt=get(aH,'CurrentPoint');
set(V,'Xdata',pt(1)*[1 1]);
set(H,'Ydata',pt(1,2)*[1 1])
end
Hope I've answered your questions there. If you can though I would seriously consider ginput