MATLAB: Modify getline() to remove 'end input on double-click' functionality - user-interface

Question

The matlab function getline (image processing toolbox) returns the position of a polyline (which has previously been defined with the cursor) either on a double-click or on pressing the return key or spacebar.
Due to my butter-fingers and accidentally double-clicking I want to remove the ability to end on a double-click.
What part do I need to change, or what functions should I be looking out for, I can't find out how a double click is even defined in matlab.
Cheers!

Answer 1

MATLAB associates "callback" functions with graphics objects, which define what to do when the mouse is clicked, keys are pressed, etc.. In getline(), the section to look at is the NextButtonDown() subfunction. This is the callback that is associated with subsequent mouse presses after the first mouse press to initiate the line. The key is that is checks the SelectionType figure property, which will be open for a double click. When that is the case, it closes the figure. So, to disable that functionality, just remove the extra case and checking logic. Here is the diff for my r2009b version:
306,310d305
< selectionType = get(GETLINE_FIG, 'SelectionType');
< if (~strcmp(selectionType, 'open'))
< % We don't want to add a point on the second click
< % of a double-click
<
322,328d316
<
< end
<
< if (~strcmp(get(GETLINE_FIG, 'SelectionType'), 'normal'))
< % We're done!
< set(GETLINE_H1, 'UserData', 'Completed');
< end

Answer 2

The answer provided by #JohnColby solves your problem by editing the GETLINE.m function file. Basically you comment out every line that check if a double-click was performed. This information is obtained by querying the 'SelectionType' figure property.
Alternatively, if you are like me and you hate making changes to built-in functions, then consider the following solution that doesn't involve changing any existing functions. Here is an example of how we use it:
h = addlistener(handle(gcf), 'WindowButtonDownFcn', 'PostSet', #changedWBDFcn);
[x,y] = getline();
delete(h)
plot(x,y, 'Color','r')
The idea is to create an event listener that gets triggered when the 'WindowButtonDownFcn' figure property changes. We use it to insert a function that gets called just before the previously set callback function (actually we replace the callback with our own function that calls the old one at the end).
This allows us to insert a section that checks if the call was triggered by a double-click, and simply skip such event.
This had to be done twice, because GETLINE first calls FirstButtonDown on first click, which sets NextButtonDown to be called on subsequent clicks, thus the use of the flag variable to differentiate between the two cases.
The code for the above event listener function:
function changedWBDFcn(src,ev,flag)
hFig = ev.AffectedObject; %# figure handle
currFcn = ev.NewValue; %# current callback function
delete(src); %# delete event listener
if nargin < 3, flag = false; end %# determine flag
%# hijack WindowButtonDownFcn function
set(hFig, 'WindowButtonDownFcn',{#wbdFcn,currFcn,flag})
%# callback function
function wbdFcn(o,e,currFcn,flag)
%# skip anything but single-clicks
if ~strcmpi(get(hFig,'SelectionType'),'normal')
return
end
%# evaluate previous callback function
hgfeval(currFcn) %# getline('FirstButtonDown'),getline('NextButtonDown')
%# repeat process after first click
if flag
addlistener(handle(hFig), 'WindowButtonDownFcn', ...
'PostSet', {#changedWBDFcn,true});
end
end
end