# R: Wait for a mouse or keyboard event from a graphics window

getGraphicsEvent {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) {
            cat("Buttons ", paste(buttons, collapse=" "), " at ", x, y, "\n")
            points(x, y)
            if (x > 0.85 && y > 0.85) "Done"
            else NULL
        }

        mousemove <- function(buttons, x, y) {
            points(x, y)
            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)

[Package grDevices version 2.6.0 Index]