grDevices (version 3.3)

getGraphicsEvent: 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,
                 consolePrompt = prompt)
setGraphicsEventHandlers(which = dev.cur(), ...)
getGraphicsEventEnv(which = dev.cur())
setGraphicsEventEnv(which = dev.cur(), env)

Arguments

prompt

prompt to be displayed to the user in the graphics window

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

consolePrompt

prompt to be displayed to the user in the console

which

which graphics device does the call apply to?

...

items including handlers to be placed in the event environment

env

an environment to be used as the event environment

Value

• When run interactively, getGraphicsEvent returns a non-NULL value returned from one of the event handlers. In a non-interactive session, getGraphicsEvent will return NULL immediately. It will also return NULL if the user closes the last window that has graphics handlers.

  getGraphicsEventEnv returns the current event environment for the graphics device, or NULL if none has been set.

  setGraphicsEventEnv and setGraphicsEventHandlers return the previous event environment for the graphics device.

code

"A"

itemize

• one of the event handlers returns a non-NULLvalue which will be returned as the value ofgetGraphicsEvent, or
• the user interrupts the function from the console.

Details

These functions allow user input from some graphics devices (currently only the windows() and X11(type = "Xlib") screen displays in base R

Examples

# This currently only works on the Windows
# and X11(type = "Xlib") screen devices...
savepar <- par(ask = FALSE)
dragplot <- function(..., xlim = NULL, ylim = NULL, xaxs = "r", yaxs = "r") {
    plot(..., xlim = xlim, ylim = ylim, xaxs = xaxs, yaxs = yaxs)
    startx <- NULL
    starty <- NULL
    prevx <- NULL
    prevy <- NULL
    usr <- NULL

    devset <- function()
        if (dev.cur() != eventEnv$which) dev.set(eventEnv$which)

    dragmousedown <- function(buttons, x, y) {
        startx <<- x
        starty <<- y
        prevx <<- 0
        prevy <<- 0
        devset()
        usr <<- par("usr")
        eventEnv$onMouseMove <- dragmousemove
        NULL
    }

    dragmousemove <- function(buttons, x, y) {
        devset()
        deltax <- diff(grconvertX(c(startx, x), "ndc", "user"))
        deltay <- diff(grconvertY(c(starty, y), "ndc", "user"))
	if (abs(deltax-prevx) + abs(deltay-prevy) > 0) {
	    plot(..., xlim = usr[1:2]-deltax, xaxs = "i",
		      ylim = usr[3:4]-deltay, yaxs = "i")
	    prevx <<- deltax
	    prevy <<- deltay
	}
        NULL
    }

    mouseup <- function(buttons, x, y) {
    	eventEnv$onMouseMove <- NULL
    }	

    keydown <- function(key) {
        if (key == "q") return(invisible(1))
        eventEnv$onMouseMove <- NULL
        NULL
    }

    setGraphicsEventHandlers(prompt = "Click and drag, hit q to quit",
                     onMouseDown = dragmousedown,
                     onMouseUp = mouseup,
                     onKeybd = keydown)
    eventEnv <- getGraphicsEventEnv()
}

dragplot(rnorm(1000), rnorm(1000))
getGraphicsEvent()
par(savepar)