gdk-GdkRGB: GdkRGB
In RGtk2: R Bindings for Gtk 2.8.0 and Above

Description Methods and Functions Detailed Description Structures Enums and Flags Author(s) References

Renders RGB, grayscale, or indexed image data to a GdkDrawable

gdkDrawRgbImage(object, gc, x, y, width, height, dith, rgb.buf, rowstride)
gdkDrawRgbImageDithalign(object, gc, x, y, width, height, dith, rgb.buf, xdith, ydith)
gdkDrawIndexedImage(object, gc, x, y, width, height, dith, buf, cmap)
gdkDrawGrayImage(object, gc, x, y, width, height, dith, buf)
gdkDrawRgb32Image(object, gc, x, y, width, height, dith, buf)
gdkDrawRgb32ImageDithalign(object, gc, x, y, width, height, dith, buf, xdith, ydith)
gdkRgbCmapNew(colors)
gdkRgbGcSetForeground(gc, rgb)
gdkRgbGcSetBackground(gc, rgb)
gdkRgbXpixelFromRgb(rgb)
gdkRgbFindColor(colormap, color)
gdkRgbSetInstall(install)
gdkRgbSetMinColors(min.colors)
gdkRgbGetVisual()
gdkRgbGetColormap()
gdkRgbDitherable()
gdkRgbColormapDitherable(colormap)
gdkRgbSetVerbose(verbose)

GdkRGB is a low-level module which renders RGB, grayscale, and indexed colormap images to a GdkDrawable. It does this as efficiently as possible, handling issues such as colormaps, visuals, dithering, temporary buffers, and so on. Most code should use the higher-level GdkPixbuf features in place of this module; for example, gdkDrawPixbuf uses GdkRGB in its implementation.

GdkRGB allocates a color cube to use when rendering images. You can set the threshold for installing colormaps with gdkRgbSetMinColors. The default is 5x5x5 (125). If a colorcube of this size or larger can be allocated in the default colormap, then that's done. Otherwise, GdkRGB creates its own private colormap. Setting it to 0 means that it always tries to use the default colormap, and setting it to 216 means that it always creates a private one if it cannot allocate the 6x6x6 colormap in the default. If you always want a private colormap (to avoid consuming too many colormap entries for other apps, say), you can use gdk_rgb_set_install(TRUE). Setting the value greater than 216 exercises a bug in older versions of GdkRGB. Note, however, that setting it to 0 doesn't let you get away with ignoring the colormap and visual - a colormap is always created in grayscale and direct color modes, and the visual is changed in cases where a "better" visual than the default is available.

If GDK is built with the Sun mediaLib library, the GdkRGB functions are accelerated using mediaLib, which provides hardware acceleration on Intel, AMD, and Sparc chipsets. If desired, mediaLib support can be turned off by setting the GDK_DISABLE_MEDIALIB environment variable.

A simple example program using GdkRGB

# Simple example of using GdkRGB with RGtk2

IMAGE_WIDTH	<- 256
IMAGE_HEIGHT <- 256


rgb_example <- function()
{
  window <- gtkWindow("toplevel", show = F)
  darea <- gtkDrawingArea()
  darea$setSizeRequest(IMAGE_WIDTH, IMAGE_HEIGHT)
  window$add(darea)
  
  # Set up the RGB buffer.
  x <- rep(0:(IMAGE_WIDTH-1), IMAGE_HEIGHT)
  y <- rep(0:(IMAGE_HEIGHT-1), IMAGE_WIDTH, each = T)
  red <- x - x %
  green <- (x / 32) * 4 + y - y %
  blue <- y - y %
  buf <- rbind(red, green, blue)
  
  # connect to expose event
  gSignalConnect(darea, "expose-event", on_darea_expose, buf)
  
  window$showAll()
}


on_darea_expose <- function(widget, event, buf)
{
  gdkDrawRgbImage(widget[["window"]],
                  widget[["style"]][["fgGc"]][[GtkStateType["normal"]+1]],
                  0, 0, IMAGE_WIDTH, IMAGE_HEIGHT, "max", buf, IMAGE_WIDTH * 3)
}

GdkRgbCmap

A private data structure which maps color indices to actual RGB colors. This is used only for gdkDrawIndexedImage. GdkRgbCmap is a transparent-type.

colors: The colors, represented as 0xRRGGBB integer values.
n_colors: The number of colors in the cmap.

GdkRgbDither

Selects whether or not GdkRGB applies dithering to the image on display.

Since GdkRGB currently only handles images with 8 bits per component, dithering on 24 bit per pixel displays is a moot point.