getGraphicsEvent          package:grDevices          R Documentation

Wait for a mouse or keyboard event from a graphics window

Description:

     This function waits for input from a graphics window in the form
     of a mouse or keyboard event.

Usage:

     getGraphicsEvent(prompt = "Waiting for input", 
                      onMouseDown = NULL, onMouseMove = NULL,
                      onMouseUp = NULL, onKeybd = NULL)

Arguments:

  prompt: prompt to be displayed to the user

onMouseDown: a function to respond to mouse clicks

onMouseMove: a function to respond to mouse movement

onMouseUp: a function to respond to mouse button releases

 onKeybd: a function to respond to key presses

Details:

     This function allows user input from some graphics devices
     (currently only the Windows screen display).  When called, event
     handlers may be  installed to respond to events involving the
     mouse or keyboard.  

     The mouse event handlers should be functions with header 
     'function(buttons, x, y)'.  The coordinates 'x' and 'y' will be
     passed to mouse event handlers in device independent coordinates
     (i.e. the lower left corner of the window is '(0,0)',  the upper
     right is '(1,1)').  The 'buttons' argument  will be a vector
     listing the buttons that are pressed at the time of the event,
     with 0 for left, 1 for middle, and 2  for right.

     The keyboard event handler should be a function with header
     'function(key)'.  A single element character vector will be passed
     to this handler, corresponding to the key press.  Shift and other
     modifier keys will have been processed, so 'shift-a' will be
     passed as '"A"'.  The following special keys may also be passed to
     the handler:

        *  Control keys, passed as '"Ctrl-A"', etc.

        *  Navigation keys, passed as one of '"Left", "Up", "Right",
           "Down", "PgUp", "PgDn", "End", "Home"'

        *  Edit keys, passed as one of '"Ins", "Del"'

        *  Function keys, passed as one of '"F1", "F2", ...'

     The event handlers are standard R functions, and will be executed
     in an environment as though they had been called directly from
     'getGraphicsEvent'.

     Events will be processed until

        *  one of the event handlers returns a non-'NULL' value which
           will be returned as the value of 'getGraphicsEvent', or 

        *  the user interrupts the function from the console.

Value:

     A non-'NULL' value returned from one of the event handlers.

Author(s):

     Duncan Murdoch

Examples:

     ## Not run: 
         mousedown <- function(buttons, x, y) {
             plx <- grconvertX(x, "ndc", "user")
             ply <- grconvertY(y, "ndc", "user")    
             cat("Buttons ", paste(buttons, collapse=" "), " at ndc",
                 x, y, "user", plx, ply, "\n")
             points(plx, ply, col="red", pch=19, cex=2)
             if (x > 0.85 && y > 0.85) "Done"
             else NULL
         }
         
         mousemove <- function(buttons, x, y) {
             plx <- grconvertX(x, "ndc", "user")
             ply <- grconvertY(y, "ndc", "user")    
             points(plx, ply)
             NULL
         }
         
         keybd <- function(key) {
             cat("Key <", key, ">\n", sep = "")
         }
         
         plot(0:1, 0:1, type='n')
         getGraphicsEvent("Click on upper right to quit",
                          onMouseDown = mousedown,
                          onMouseMove = mousemove,
                          onKeybd = keybd)
     ## End(Not run)

