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window <- NULL
# Pixmap for scribble area, to store current scribbles
pixmap <- NULL
# Create a new pixmap of the appropriate size to store our scribbles
scribble.configure.event <- function(widget, event, data)
{
pixmap <<- gdkPixmapNew(widget[["window"]], widget[["allocation"]][["width"]],
widget[["allocation"]][["height"]], -1)
# Initialize the pixmap to white
cr <- gdkCairoCreate(pixmap)
cr$setSourceRgb(1, 1, 1)
cr$paint()
# We've handled the configure event, no need for further processing.
return(TRUE)
}
# Redraw the screen from the pixmap
scribble.expose.event <- function(widget, event, data)
{
# We use the "foreground GC" for the widget since it already exists,
# but honestly any GC would work. The only thing to worry about
# is whether the GC has an inappropriate clip region set.
#
cr <- gdkCairoCreate(widget[["window"]])
gdkCairoSetSourcePixmap(cr, pixmap, 0, 0)
gdkCairoRectangle(cr, event[["area"]])
cr$fill()
return(FALSE)
}
# Draw a rectangle on the screen
draw.brush <- function(widget, x, y)
{
update.rect <- c(x=x-3, y=y-3, width=6, height=6)
cr <- gdkCairoCreate(pixmap)
gdkCairoRectangle(cr, update.rect)
cr$fill()
# Now invalidate the affected region of the drawing area. (so it will be updated)
gdkWindowInvalidateRect(widget[["window"]], update.rect, FALSE)
}
scribble.button.press.event <- function(widget, event, data)
{
if (is.null(pixmap))
return(FALSE) # paranoia check, in case we haven't gotten a configure event
if (event[["button"]] == 1) # left mouse button click
draw.brush(widget, event[["x"]], event[["y"]])
# We've handled the event, stop processing
return(TRUE)
}
scribble.motion.notify.event <- function(widget, event, data)
{
if (is.null(pixmap))
return(FALSE) # paranoia check, in case we haven't gotten a configure event
# This call is very important it requests the next motion event.
# If you don't call gdkWindowGetPointer() you'll only get
# a single motion event. The reason is that we specified
# GDK_POINTER_MOTION_HINT_MASK to gtkWidgetSetEvents().
# If we hadn't specified that, we could just use event[["x"]], event[["y"]]
# as the pointer location. But we'd also get deluged in events.
# By requesting the next event as we handle the current one,
# we avoid getting a huge number of events faster than we
# can cope.
#
pointer <- gdkWindowGetPointer(event[["window"]])
# if button1 held down, draw
if (as.flag(pointer$mask) & GdkModifierType["button1-mask"])
draw.brush(widget, pointer$x, pointer$y)
# We've handled it, stop processing
return(TRUE)
}
checkerboard.expose <- function(da, event, data)
{
CHECK.SIZE <- 10
SPACING <- 2
# At the start of an expose handler, a clip region of event[["area"]]
# is set on the window, and event[["area"]] has been cleared to the
# widget's background color. The docs for
# gdkWindowBeginPaintRegion() give more details on how this
# works.
#
cr <- gdkCairoCreate(da[["window"]])
gdkCairoRectangle(cr, event[["area"]])
cr$clip()
xcount <- 0
i <- SPACING
while (i < da[["allocation"]][["width"]])
{
j <- SPACING
ycount <- xcount %% 2 # start with even/odd depending on row
while (j < da[["allocation"]][["height"]])
{
if (ycount %% 2)
cr$setSourceRgb(0.45777, 0, 0.45777)
else
cr$setSourceRgb(1, 1, 1)
# If we're outside event->area, this will do nothing.
# It might be mildly more efficient if we handled
# the clipping ourselves, but again we're feeling lazy.
#
cr$rectangle(i, j, CHECK.SIZE, CHECK.SIZE)
cr$fill()
j <- j + CHECK.SIZE + SPACING
ycount <- ycount + 1
}
i <- i + CHECK.SIZE + SPACING
xcount <- xcount + 1
}
# return TRUE because we've handled this event, so no
# further processing is performed
#
return(TRUE)
}
window <- gtkWindowNew("toplevel", show=F)
window$setTitle("Drawing Area")
window$setBorderWidth(8)
vbox <- gtkVBoxNew(FALSE, 8)
vbox$setBorderWidth(8)
window$add(vbox)
#
# Create the checkerboard area
#
label <- gtkLabelNew()
label$setMarkup("<u>Checkerboard pattern</u>")
vbox$packStart(label, FALSE, FALSE, 0)
frame <- gtkFrameNew()
frame$setShadowType("in")
vbox$packStart(frame, TRUE, TRUE, 0)
da <- gtkDrawingAreaNew(show=F)
# set a minimum size
da$setSizeRequest(100, 100)
frame$add(da)
gSignalConnect(da, "expose_event", checkerboard.expose)
#
# Create the scribble area
#
label <- gtkLabelNew()
label$setMarkup("<u>Scribble area</u>")
vbox$packStart(label, FALSE, FALSE, 0)
frame <- gtkFrameNew()
frame$setShadowType("in")
vbox$packStart(frame, TRUE, TRUE, 0)
da <- gtkDrawingAreaNew()
# set a minimum size
da$setSizeRequest(100, 100)
frame$add(da)
# Signals used to handle backing pixmap
gSignalConnect(da, "expose_event", scribble.expose.event)
gSignalConnect(da, "configure_event", scribble.configure.event)
# Event signals
gSignalConnect(da, "motion_notify_event", scribble.motion.notify.event)
gSignalConnect(da, "button_press_event", scribble.button.press.event)
# Ask to receive events the drawing area doesn't normally
# subscribe to
#
# we have to do this numerically, because the function takes gint, not GdkEventMask
da$setEvents(da$getEvents() + GdkEventMask["button-press-mask"] +
GdkEventMask["pointer-motion-mask"] + GdkEventMask["pointer-motion-hint-mask"])
window$showAll()
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