GdkPixbufLoader

The gdk-pixbuf Library
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GdkPixbufLoader — Application-driven progressive image loading.

Synopsis


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


GdkPixbufLoader* gdk_pixbuf_loader_new      (void);
GdkPixbufLoader* gdk_pixbuf_loader_new_with_type
                                            (const char *image_type,
                                             GError **error);
gboolean    gdk_pixbuf_loader_write         (GdkPixbufLoader *loader,
                                             const guchar *buf,
                                             gsize count,
                                             GError **error);
void        gdk_pixbuf_loader_set_size      (GdkPixbufLoader *loader,
                                             int width,
                                             int height);
GdkPixbuf*  gdk_pixbuf_loader_get_pixbuf    (GdkPixbufLoader *loader);
GdkPixbufAnimation* gdk_pixbuf_loader_get_animation
                                            (GdkPixbufLoader *loader);
gboolean    gdk_pixbuf_loader_close         (GdkPixbufLoader *loader,
                                             GError **error);

Description

GdkPixbufLoader provides a way for applications to drive the process of loading an image, by letting them send the image data directly to the loader instead of having the loader read the data from a file. Applications can use this functionality instead of gdk_pixbuf_new_from_file() or gdk_pixbuf_animation_new_from_file() when they need to parse image data in small chunks. For example, it should be used when reading an image from a (potentially) slow network connection, or when loading an extremely large file.

To use GdkPixbufLoader to load an image, just create a new one, and call gdk_pixbuf_loader_write() to send the data to it. When done, gdk_pixbuf_loader_close() should be called to end the stream and finalize everything. The loader will emit three important signals throughout the process. The first, "size_prepared", will be called as soon as the image has enough information to determine the size of the image to be used. If you want to scale the image while loading it, you can call gdk_pixbuf_loader_set_size() in response to this signal.

The second signal, "area_prepared", will be called as soon as the pixbuf of the desired has been allocated. You can obtain it by calling gdk_pixbuf_loader_get_pixbuf(). If you want to use it, simply ref it. In addition, no actual information will be passed in yet, so the pixbuf can be safely filled with any temporary graphics (or an initial color) as needed. You can also call gdk_pixbuf_loader_get_pixbuf() later and get the same pixbuf.

The last signal, "area_updated" gets called every time a region is updated. This way you can update a partially completed image. Note that you do not know anything about the completeness of an image from the area updated. For example, in an interlaced image, you need to make several passes before the image is done loading.

Loading an animation

Loading an animation is almost as easy as loading an image. Once the first "area_prepared" signal has been emitted, you can call gdk_pixbuf_loader_get_animation() to get the GdkPixbufAnimation struct and gdk_pixbuf_animation_get_iter() to get an GdkPixbufAnimationIter for displaying it.

Details

gdk_pixbuf_loader_new ()

GdkPixbufLoader* gdk_pixbuf_loader_new      (void);

Creates a new pixbuf loader object.

Returns :

A newly-created pixbuf loader.

gdk_pixbuf_loader_new_with_type ()

GdkPixbufLoader* gdk_pixbuf_loader_new_with_type
                                            (const char *image_type,
                                             GError **error);

Creates a new pixbuf loader object that always attempts to parse image data as if it were an image of type image_type, instead of identifying the type automatically. Useful if you want an error if the image isn't the expected type, for loading image formats that can't be reliably identified by looking at the data, or if the user manually forces a specific type.

`image_type` :	name of the image format to be loaded with the image
`error` :	return location for an allocated GError, or `NULL` to ignore errors
Returns :	A newly-created pixbuf loader.

gdk_pixbuf_loader_write ()

gboolean    gdk_pixbuf_loader_write         (GdkPixbufLoader *loader,
                                             const guchar *buf,
                                             gsize count,
                                             GError **error);

This will cause a pixbuf loader to parse the next count bytes of an image. It will return TRUE if the data was loaded successfully, and FALSE if an error occurred. In the latter case, the loader will be closed, and will not accept further writes. If FALSE is returned, error will be set to an error from the GDK_PIXBUF_ERROR or G_FILE_ERROR domains.

`loader` :	A pixbuf loader.
`buf` :	Pointer to image data.
`count` :	Length of the `buf` buffer in bytes.
`error` :	return location for errors
Returns :	`TRUE` if the write was successful, or `FALSE` if the loader cannot parse the buffer.

gdk_pixbuf_loader_set_size ()

void        gdk_pixbuf_loader_set_size      (GdkPixbufLoader *loader,
                                             int width,
                                             int height);

Causes the image to be scaled while it is loaded. The desired image size can be determined relative to the original size of the image by calling gdk_pixbuf_loader_set_size() from a signal handler for the ::size_prepared signal.

Attempts to set the desired image size are ignored after the emission of the ::size_prepared signal.

`loader` :	A pixbuf loader.
`width` :	The desired width of the image being loaded.
`height` :	The desired height of the image being loaded.

gdk_pixbuf_loader_get_pixbuf ()

GdkPixbuf*  gdk_pixbuf_loader_get_pixbuf    (GdkPixbufLoader *loader);

Queries the GdkPixbuf that a pixbuf loader is currently creating. In general it only makes sense to call this function after the "area_prepared" signal has been emitted by the loader; this means that enough data has been read to know the size of the image that will be allocated. If the loader has not received enough data via gdk_pixbuf_loader_write(), then this function returns NULL. The returned pixbuf will be the same in all future calls to the loader, so simply calling g_object_ref() should be sufficient to continue using it. Additionally, if the loader is an animation, it will return the "static image" of the animation (see gdk_pixbuf_animation_get_static_image()).

`loader` :	A pixbuf loader.
Returns :	The GdkPixbuf that the loader is creating, or `NULL` if not enough data has been read to determine how to create the image buffer.

gdk_pixbuf_loader_get_animation ()

GdkPixbufAnimation* gdk_pixbuf_loader_get_animation
                                            (GdkPixbufLoader *loader);

Queries the GdkPixbufAnimation that a pixbuf loader is currently creating. In general it only makes sense to call this function after the "area_prepared" signal has been emitted by the loader. If the loader doesn't have enough bytes yet (hasn't emitted the "area_prepared" signal) this function will return NULL.

`loader` :	A pixbuf loader
Returns :	The GdkPixbufAnimation that the loader is loading, or `NULL` if not enough data has been read to determine the information.

gdk_pixbuf_loader_close ()

gboolean    gdk_pixbuf_loader_close         (GdkPixbufLoader *loader,
                                             GError **error);

Informs a pixbuf loader that no further writes with gdk_pixbuf_loader_write() will occur, so that it can free its internal loading structures. Also, tries to parse any data that hasn't yet been parsed; if the remaining data is partial or corrupt, an error will be returned. If FALSE is returned, error will be set to an error from the GDK_PIXBUF_ERROR or G_FILE_ERROR domains. If you're just cancelling a load rather than expecting it to be finished, passing NULL for error to ignore it is reasonable.

`loader` :	A pixbuf loader.
`error` :	return location for a GError, or `NULL` to ignore errors
Returns :	`TRUE` if all image data written so far was successfully passed out via the update_area signal