Pango is the text layout system used by GDK and GTK+. The functions
and types in this section are used to render Pango objects to GDK.
drawables, and also extend the set of Pango attributes to include
stippling and embossing. Creating a PangoLayout object is the first step in rendering text,
and requires getting a handle to a PangoContext. For GTK+ programs,
you'll usually want to use gtkWidgetGetPangoContext, or
gtkWidgetCreatePangoLayout, rather than using the lowlevel
gdkPangoContextGetForScreen. Once you have a PangoLayout, you
can set the text and attributes of it with Pango functions like
pangoLayoutSetText and get its size with pangoLayoutGetSize.
(Note that Pango uses a fixed point system internally, so converting
between Pango units and pixels using PANGO_SCALE or the pangoPixels() function.) Rendering a Pango layout is done most simply with gdkDrawLayout;
you can also draw pieces of the layout with gdkDrawLayout or
gdkDrawGlyphs. GdkPangoRenderer is a subclass of PangoRenderer
that is used internally to implement these functions. Using it
directly or subclassing it can be useful in some cases. See the
GdkPangoRenderer documentation for details. Using GdkPangoRenderer to draw transformed text
window <- NULL RADIUS <- 150
N.WORDS <- 10
FONT <- "Sans Bold 27" rotated.text.expose.event <- function(widget, event, data)
{ ## matrix describing font transformation, initialize to identity
matrix <- pangoMatrixInit() width <- widget[["allocation"]][["width"]]
height <- widget[["allocation"]][["height"]] ## Get the default renderer for the screen, and set it up for drawing
renderer <- gdkPangoRendererGetDefault(widget$getScreen())
renderer$setDrawable(widget[["window"]])
renderer$setGc(widget[["style"]][["blackGc"]]) ## Set up a transformation matrix so that the user space coordinates for
## the centered square where we draw are [-RADIUS, RADIUS], [-RADIUS, RADIUS]
## We first center, then change the scale
device.radius <- min(width, height) / 2.
matrix$translate(device.radius + (width - 2 * device.radius) / 2,
device.radius + (height - 2 * device.radius) / 2)
matrix$scale(device.radius / RADIUS, device.radius / RADIUS) ## Create a PangoLayout, set the font and text
context <- widget$createPangoContext()
layout <- pangoLayoutNew(context)
layout$setText("Text")
desc <- pangoFontDescriptionFromString(FONT)
layout$setFontDescription(desc) # Draw the layout N.WORDS times in a circle
for (i in 1:N.WORDS) {
rotated.matrix <- matrix$copy()
angle <- (360 * i) / N.WORDS color <- list()
## Gradient from red at angle 60 to blue at angle 300
color$red <- 65535 * (1 + cos((angle - 60) * pi / 180)) / 2
color$green <- 0
color$blue <- 65535 - color$red renderer$setOverrideColor("foreground", color) rotated.matrix$rotate(angle) context$setMatrix(rotated.matrix) ## Inform Pango to re-layout the text with the new transformation matrix
layout$contextChanged() size <- layout$getSize()
renderer$drawLayout(layout, - size$width / 2, - RADIUS * 1024)
} ## Clean up default renderer, since it is shared
renderer$setOverrideColor("foreground", NULL)
renderer$setDrawable(NULL)
renderer$setGc(NULL) return(FALSE)
} white <- c( 0, "0xffff", "0xffff", "0xffff" ) window <- gtkWindowNew("toplevel")
window$setTitle("Rotated Text")
drawing.area <- gtkDrawingAreaNew()
window$add(drawing.area) # This overrides the background color from the theme
drawing.area$modifyBg("normal", white) gSignalConnect(drawing.area, "expose-event", rotated.text.expose.event) window$setDefaultSize(2 * RADIUS, 2 * RADIUS) window$showAll()