The GdkPixbuf Structure

The GdkPixbuf Structure — Information that describes an image.

Synopsis

#include <gdk-pixbuf/gdk-pixbuf.h>


enum        GdkPixbufError;
#define     GDK_PIXBUF_ERROR
enum        GdkColorspace;
enum        GdkPixbufAlphaMode;
            GdkPixbuf;
GdkColorspace gdk_pixbuf_get_colorspace     (const GdkPixbuf *pixbuf);
int         gdk_pixbuf_get_n_channels       (const GdkPixbuf *pixbuf);
gboolean    gdk_pixbuf_get_has_alpha        (const GdkPixbuf *pixbuf);
int         gdk_pixbuf_get_bits_per_sample  (const GdkPixbuf *pixbuf);
guchar*     gdk_pixbuf_get_pixels           (const GdkPixbuf *pixbuf);
int         gdk_pixbuf_get_width            (const GdkPixbuf *pixbuf);
int         gdk_pixbuf_get_height           (const GdkPixbuf *pixbuf);
int         gdk_pixbuf_get_rowstride        (const GdkPixbuf *pixbuf);
const gchar* gdk_pixbuf_get_option          (GdkPixbuf *pixbuf,
                                             const gchar *key);


Object Hierarchy

  GObject
   +----GdkPixbuf

Properties

  "bits-per-sample"      gint                  : Read / Write / Construct Only
  "colorspace"           GdkColorspace         : Read / Write / Construct Only
  "has-alpha"            gboolean              : Read / Write / Construct Only
  "height"               gint                  : Read / Write / Construct Only
  "n-channels"           gint                  : Read / Write / Construct Only
  "pixels"               gpointer              : Read / Write / Construct Only
  "rowstride"            gint                  : Read / Write / Construct Only
  "width"                gint                  : Read / Write / Construct Only

Description

The GdkPixbuf structure contains information that describes an image in memory.

Image Data

Image data in a pixbuf is stored in memory in uncompressed, packed format. Rows in the image are stored top to bottom, and in each row pixels are stored from left to right. There may be padding at the end of a row. The "rowstride" value of a pixbuf, as returned by gdk_pixbuf_get_rowstride(), indicates the number of bytes between rows.

Example 1. put_pixel() example

The following code illustrates a simple put_pixel() function for RGB pixbufs with 8 bits per channel with an alpha channel. It is not included in the gdk-pixbuf library for performance reasons; rather than making several function calls for each pixel, your own code can take shortcuts.

static void
put_pixel (GdkPixbuf *pixbuf, int x, int y, guchar red, guchar green, guchar blue, guchar alpha)
{
  int width, height, rowstride, n_channels;
  guchar *pixels, *p;

  n_channels = gdk_pixbuf_get_n_channels (pixbuf);

  g_assert (gdk_pixbuf_get_colorspace (pixbuf) == GDK_COLORSPACE_RGB);
  g_assert (gdk_pixbuf_get_bits_per_sample (pixbuf) == 8);
  g_assert (gdk_pixbuf_get_has_alpha (pixbuf));
  g_assert (n_channels == 4);

  width = gdk_pixbuf_get_width (pixbuf);
  height = gdk_pixbuf_get_height (pixbuf);

  g_assert (x >= 0 && x < width);
  g_assert (y >= 0 && y < height);

  rowstride = gdk_pixbuf_get_rowstride (pixbuf);
  pixels = gdk_pixbuf_get_pixels (pixbuf);

  p = pixels + y * rowstride + x * n_channels;
  p[0] = red;
  p[1] = green;
  p[2] = blue;
  p[3] = alpha;
}
      

This function will not work for pixbufs with images that are other than 8 bits per sample or channel, but it will work for most of the pixbufs that GTK+ uses.

Note

If you are doing memcpy() of raw pixbuf data, note that the last row in the pixbuf may not be as wide as the full rowstride, but rather just as wide as the pixel data needs to be. That is, it is unsafe to do memcpy (dest, pixels, rowstride * height) to copy a whole pixbuf. Use gdk_pixbuf_copy() instead, or compute the width in bytes of the last row as width * ((n_channels * bits_per_sample + 7) / 8).

Details

enum GdkPixbufError

typedef enum {
        /* image data hosed */
        GDK_PIXBUF_ERROR_CORRUPT_IMAGE,
        /* no mem to load image */
        GDK_PIXBUF_ERROR_INSUFFICIENT_MEMORY,
        /* bad option passed to save routine */
        GDK_PIXBUF_ERROR_BAD_OPTION,
        /* unsupported image type (sort of an ENOSYS) */
        GDK_PIXBUF_ERROR_UNKNOWN_TYPE,
        /* unsupported operation (load, save) for image type */
        GDK_PIXBUF_ERROR_UNSUPPORTED_OPERATION,
        GDK_PIXBUF_ERROR_FAILED
} GdkPixbufError;

An error code in the GDK_PIXBUF_ERROR domain. Many gdk-pixbuf operations can cause errors in this domain, or in the G_FILE_ERROR domain.

GDK_PIXBUF_ERROR_CORRUPT_IMAGEAn image file was broken somehow.
GDK_PIXBUF_ERROR_INSUFFICIENT_MEMORYNot enough memory.
GDK_PIXBUF_ERROR_BAD_OPTIONA bad option was passed to a pixbuf save module.
GDK_PIXBUF_ERROR_UNKNOWN_TYPEUnknown image type.
GDK_PIXBUF_ERROR_UNSUPPORTED_OPERATIONDon't know how to perform the given operation on the type of image at hand.
GDK_PIXBUF_ERROR_FAILEDGeneric failure code, something went wrong.

GDK_PIXBUF_ERROR

#define GDK_PIXBUF_ERROR gdk_pixbuf_error_quark ()

Error domain used for pixbuf operations. Indicates that the error code will be in the GdkPixbufError enumeration. See GError for information on error domains and error codes.


enum GdkColorspace

typedef enum {
	GDK_COLORSPACE_RGB
} GdkColorspace;

This enumeration defines the color spaces that are supported by the gdk-pixbuf library. Currently only RGB is supported.

GDK_COLORSPACE_RGBIndicates a red/green/blue additive color space.

enum GdkPixbufAlphaMode

typedef enum
{
        GDK_PIXBUF_ALPHA_BILEVEL,
        GDK_PIXBUF_ALPHA_FULL
} GdkPixbufAlphaMode;

These values can be passed to gdk_pixbuf_render_to_drawable_alpha() to control how the alpha channel of an image should be handled. This function can create a bilevel clipping mask (black and white) and use it while painting the image. In the future, when the X Window System gets an alpha channel extension, it will be possible to do full alpha compositing onto arbitrary drawables. For now both cases fall back to a bilevel clipping mask.

GDK_PIXBUF_ALPHA_BILEVELA bilevel clipping mask (black and white) will be created and used to draw the image. Pixels below 0.5 opacity will be considered fully transparent, and all others will be considered fully opaque.
GDK_PIXBUF_ALPHA_FULLFor now falls back to GDK_PIXBUF_ALPHA_BILEVEL. In the future it will do full alpha compositing.

GdkPixbuf

typedef struct _GdkPixbuf GdkPixbuf;

This is the main structure in the gdk-pixbuf library. It is used to represent images. It contains information about the image's pixel data, its color space, bits per sample, width and height, and the rowstride (the number of bytes between the start of one row and the start of the next).


gdk_pixbuf_get_colorspace ()

GdkColorspace gdk_pixbuf_get_colorspace     (const GdkPixbuf *pixbuf);

Queries the color space of a pixbuf.

pixbuf : A pixbuf.
Returns : Color space.

gdk_pixbuf_get_n_channels ()

int         gdk_pixbuf_get_n_channels       (const GdkPixbuf *pixbuf);

Queries the number of channels of a pixbuf.

pixbuf : A pixbuf.
Returns : Number of channels.

gdk_pixbuf_get_has_alpha ()

gboolean    gdk_pixbuf_get_has_alpha        (const GdkPixbuf *pixbuf);

Queries whether a pixbuf has an alpha channel (opacity information).

pixbuf : A pixbuf.
Returns : TRUE if it has an alpha channel, FALSE otherwise.

gdk_pixbuf_get_bits_per_sample ()

int         gdk_pixbuf_get_bits_per_sample  (const GdkPixbuf *pixbuf);

Queries the number of bits per color sample in a pixbuf.

pixbuf : A pixbuf.
Returns : Number of bits per color sample.

gdk_pixbuf_get_pixels ()

guchar*     gdk_pixbuf_get_pixels           (const GdkPixbuf *pixbuf);

Queries a pointer to the pixel data of a pixbuf.

pixbuf : A pixbuf.
Returns : A pointer to the pixbuf's pixel data. Please see the section called “Image Data” for information about how the pixel data is stored in memory.

gdk_pixbuf_get_width ()

int         gdk_pixbuf_get_width            (const GdkPixbuf *pixbuf);

Queries the width of a pixbuf.

pixbuf : A pixbuf.
Returns : Width in pixels.

gdk_pixbuf_get_height ()

int         gdk_pixbuf_get_height           (const GdkPixbuf *pixbuf);

Queries the height of a pixbuf.

pixbuf : A pixbuf.
Returns : Height in pixels.

gdk_pixbuf_get_rowstride ()

int         gdk_pixbuf_get_rowstride        (const GdkPixbuf *pixbuf);

Queries the rowstride of a pixbuf, which is the number of bytes between the start of a row and the start of the next row.

pixbuf : A pixbuf.
Returns : Distance between row starts.

gdk_pixbuf_get_option ()

const gchar* gdk_pixbuf_get_option          (GdkPixbuf *pixbuf,
                                             const gchar *key);

Looks up key in the list of options that may have been attached to the pixbuf when it was loaded.

pixbuf : a GdkPixbuf
key : a nul-terminated string.
Returns : the value associated with key. This is a nul-terminated string that should not be freed or NULL if key was not found.

Properties

The "bits-per-sample" property

  "bits-per-sample"      gint                  : Read / Write / Construct Only

The number of bits per sample. Currently only 8 bit per sample are supported.

Allowed values: [1,16]

Default value: 8


The "colorspace" property

  "colorspace"           GdkColorspace         : Read / Write / Construct Only

The colorspace in which the samples are interpreted.

Default value: GDK_COLORSPACE_RGB


The "has-alpha" property

  "has-alpha"            gboolean              : Read / Write / Construct Only

Whether the pixbuf has an alpha channel.

Default value: FALSE


The "height" property

  "height"               gint                  : Read / Write / Construct Only

The number of rows of the pixbuf.

Allowed values: >= 1

Default value: 1


The "n-channels" property

  "n-channels"           gint                  : Read / Write / Construct Only

The number of samples per pixel. Currently, only 3 or 4 samples per pixel are supported.

Allowed values: >= 0

Default value: 3


The "pixels" property

  "pixels"               gpointer              : Read / Write / Construct Only

A pointer to the pixel data of the pixbuf.


The "rowstride" property

  "rowstride"            gint                  : Read / Write / Construct Only

The number of bytes between the start of a row and the start of the next row. This number must (obviously) be at least as large as the width of the pixbuf.

Allowed values: >= 1

Default value: 1


The "width" property

  "width"                gint                  : Read / Write / Construct Only

The number of columns of the pixbuf.

Allowed values: >= 1

Default value: 1