The locations of the endpoints of the arrow, as a two-row
matrix. The first row indicates the location of the tail of the
arrow; the second row indicates the location of the head of the
arrow.
Arguments
reverse
If FALSE, first indicate the tail of the arrow and
then the head; if TRUE, first indicate the head of the arrow and then
the tail.
horizontal
If TRUE, force the arrow to be horizontal. (Use the
average y-axis value of the two clicks for the vertical placement.)
vertical
If TRUE, force the arrow to be vertical. (Use the
average x-axis value of the two clicks for the horizontal placement.)
length
Length of the edges of the arrow head.
...
Additional graphics parameters
Details
Use graphics::locator() to indicate the two endpoints of
an arrow and then draw it.