gdk-pixbuf-scaling: Scaling
In RGtk2: R Bindings for Gtk 2.8.0 and Above

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

Scaling pixbufs and scaling and compositing pixbufs

gdkPixbufScaleSimple(object, dest.width, dest.height, interp.type)
gdkPixbufScale(object, dest, dest.x, dest.y, dest.width, dest.height, offset.x, offset.y, scale.x, scale.y, interp.type)
gdkPixbufCompositeColorSimple(object, dest.width, dest.height, interp.type, overall.alpha, check.size, color1, color2)
gdkPixbufComposite(object, dest, dest.x, dest.y, dest.width, dest.height, offset.x, offset.y, scale.x, scale.y, interp.type, overall.alpha)
gdkPixbufCompositeColor(object, dest, dest.x, dest.y, dest.width, dest.height, offset.x, offset.y, scale.x, scale.y, interp.type, overall.alpha, check.x, check.y, check.size, color1, color2)
gdkPixbufRotateSimple(object, angle)
gdkPixbufFlip(object, horizontal)

The gdk-pixbuf contains functions to scale pixbufs, to scale pixbufs and composite against an existing image, and to scale pixbufs and composite against a solid color or checkerboard. Compositing a checkerboard is a common way to show an image with an alpha channel in image-viewing and editing software.

Since the full-featured functions (gdkPixbufScale, gdkPixbufComposite, and gdkPixbufCompositeColor) are rather complex to use and have many arguments, two simple convenience functions are provided, gdkPixbufScaleSimple and gdkPixbufCompositeColorSimple which create a new pixbuf of a given size, scale an original image to fit, and then return the new pixbuf.

Scaling and compositing functions take advantage of MMX hardware acceleration on systems where MMX is supported. If gdk-pixbuf is built with the Sun mediaLib library, these functions are instead 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.

The following example demonstrates handling an expose event by rendering the appropriate area of a source image (which is scaled to fit the widget) onto the widget's window. The source image is rendered against a checkerboard, which provides a visual representation of the alpha channel if the image has one. If the image doesn't have an alpha channel, calling gdkPixbufCompositeColor function has exactly the same effect as calling gdkPixbufScale.

Handling an expose event.

expose_cb <- function(widget, event, data)
{
  dest <- gdkPixbuf(color = "rgb", has.alpha = FALSE, bits = 8, 
                    w = event[["area"]]$width, h = event[["area"]]$height)

  area <- event[["area"]]
  pixbuf$compositeColor(dest, 0, 0, area$width, area$height,
                        -area$x, -area$y,
                        widget[["allocation"]]$width / pixbuf$getWidth(),
                        widget[["allocation"]]$height / pixbuf$getHeight(),
                        "bilinear", 255,
                        area$x, area$y, 16, 0xaaaaaa, 0x555555)

  dest$renderToDrawable(widget[["window"]],
                        widget[["style"]][["fgGc"]][[GtkStateType["normal"]+1]],
                        0, 0, area$x, area$y,
                        area$width, area$height,
                        "normal", area$x, area$y)

  return(TRUE)
}

GdkInterpType

This enumeration describes the different interpolation modes that can be used with the scaling functions. GDK.INTERP.NEAREST is the fastest scaling method, but has horrible quality when scaling down. GDK.INTERP.BILINEAR is the best choice if you aren't sure what to choose, it has a good speed/quality balance. PLEASE NOTE: Cubic filtering is missing from the list; hyperbolic interpolation is just as fast and results in higher quality.

nearest: Nearest neighbor sampling; this is the fastest and lowest quality mode. Quality is normally unacceptable when scaling down, but may be OK when scaling up.
tiles: This is an accurate simulation of the PostScript image operator without any interpolation enabled. Each pixel is rendered as a tiny parallelogram of solid color, the edges of which are implemented with antialiasing. It resembles nearest neighbor for enlargement, and bilinear for reduction.
bilinear: Best quality/speed balance; use this mode by default. Bilinear interpolation. For enlargement, it is equivalent to point-sampling the ideal bilinear-interpolated image. For reduction, it is equivalent to laying down small tiles and integrating over the coverage area.
hyper: This is the slowest and highest quality reconstruction function. It is derived from the hyperbolic filters in Wolberg's "Digital Image Warping", and is formally defined as the hyperbolic-filter sampling the ideal hyperbolic-filter interpolated image (the filter is designed to be idempotent for 1:1 pixel mapping).

GdkPixbufRotation