gtk:text-view-line-at-y (view y)

view -- a gtk:text-view widget
y -- an integer with the y coordinate

iter -- a gtk:text-iter iterator
line -- an integer with the top coordinate of the line

Gets the gtk:text-iter iterator at the start of the line containing the coordinate y. The y argument is in text buffer coordinates, convert from window coordinates with the gtk:text-view-window-to-buffer-coords function. If non-nil, line will be filled with the coordinate of the top edge of the line.