demo/pangoCairo.R

In RGtk2: R Bindings for Gtk 2.8.0 and Above

RADIUS <- 150
N.WORDS <- 10
FONT <- "Sans Bold 27"

draw.text <- function(widget, event, data)
{
	width <- widget[["allocation"]][["width"]]
    height <- widget[["allocation"]][["height"]]
  
	device.radius <- min(width, height) / 2.
  
	cr <- gdkCairoCreate(widget[["window"]])
	
	# Center coordinates on the middle of the region we are drawing
	cr$translate(device.radius + (width - 2 * device.radius) / 2,
              device.radius + (height - 2 * device.radius) / 2)
	cr$scale(device.radius / RADIUS, device.radius / RADIUS)
	
	# Create a PangoLayout, set the font and text
	layout <- pangoCairoCreateLayout(cr)
  
	layout$setText("Text")
	desc <- pangoFontDescriptionFromString(FONT)
	layout$setFontDescription(desc)
  
  # Draw the layout N.WORDS times in a circle
  for (i in 1:N.WORDS)
    {
      angle <- (360 * i) / N.WORDS
      
	  cr$save()

      # Gradient from red at angle 60 to blue at angle 300
      red <- (1 + cos((angle - 60) * pi / 180)) / 2
      cr$setSourceRgb(red, 0, 1.0 - red)

      cr$rotate(angle * pi / 180)
    
      # Inform Pango to re-layout the text with the new transformation
      pangoCairoUpdateLayout(cr, layout)
    
      size <- layout$getSize()
      cr$moveTo(- (size$width / PANGO_SCALE) / 2, - RADIUS)
      pangoCairoShowLayout(cr, layout)

      cr$restore()
    }
	return(FALSE)
}

white <- c( 0, "0xffff", "0xffff", "0xffff" )

window <- gtkWindowNew("toplevel", show = F)
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", draw.text)

window$showAll()