This function works with a DNA alignment (freshly) plotted on an
interactive graphical device (i.e., not a file) with image
.
After calling alex
, the user clicks twice defining a rectangle
in the alignment, then this portion of the alignment is extacted and
plotted on a new window. The user can click as many times on
the alignment. The process is stopped by a right-click. If the user
clicks twice outside the alignment, a message ``Try again!'' is
printed. Each time alex
is called, the alignment is plotted on a new
window without closing or deleting those possibly already plotted.
In all cases, the device where x
is plotted is the active
window after the operation. It should not be closed during the
whole process.