grid.locator              package:grid              R Documentation

_C_a_p_t_u_r_e _a _M_o_u_s_e _C_l_i_c_k

_D_e_s_c_r_i_p_t_i_o_n:

     Allows the user to click the mouse once within the current
     graphics device and returns the location of the mouse click within
     the current viewport, in the specified coordinate system.

_U_s_a_g_e:

     grid.locator(unit = "native")

_A_r_g_u_m_e_n_t_s:

    unit: The coordinate system in which to return the location of the
          mouse click. See the 'unit' function for valid coordinate
          systems.

_D_e_t_a_i_l_s:

     This function is modal (like the graphics package function
     'locator') so the command line and graphics drawing is blocked
     until the use has clicked the mouse  in the current device.

_V_a_l_u_e:

     A unit object representing the location of the mouse click within
     the current viewport, in the specified coordinate system.

     If the user did not click mouse button 1, the function (invisibly)
     returns 'NULL'.

_A_u_t_h_o_r(_s):

     Paul Murrell

_S_e_e _A_l_s_o:

     'viewport', 'unit', 'locator' in package graphics, and for an
     application see 'trellis.focus' and 'trellis.identify' in package
     lattice.

_E_x_a_m_p_l_e_s:

     if (interactive()) {
       ## Need to write a more sophisticated unit as.character method
       unittrim <- function(unit) {
         sub("^([0-9]+|[0-9]+[.][0-9])[0-9]*", "\\1", as.character(unit))
       }
       do.click <- function(unit) {
         click.locn <- grid.locator(unit)
         grid.segments(unit.c(click.locn$x, unit(0, "npc")),
                       unit.c(unit(0, "npc"), click.locn$y),
                       click.locn$x, click.locn$y,
                       gp=gpar(lty="dashed", col="grey"))
         grid.points(click.locn$x, click.locn$y, pch=16, size=unit(1, "mm"))
         clickx <- unittrim(click.locn$x)
         clicky <- unittrim(click.locn$y)
         grid.text(paste("(", clickx, ", ", clicky, ")", sep=""),
                   click.locn$x + unit(2, "mm"), click.locn$y,
                   just="left")
       }
       do.click("inches")
       pushViewport(viewport(width=0.5, height=0.5,
                              xscale=c(0, 100), yscale=c(0, 10)))
       grid.rect()
       grid.xaxis()
       grid.yaxis()
       do.click("native")
       popViewport()  
     }

