manpagez: man pages & more
html files: gdk-pixbuf
Home | html | info | man

GdkPixbufLoader

GdkPixbufLoader — Application-driven progressive image loading.

Types and Values

Object Hierarchy

    GObject
    ╰── GdkPixbufLoader

Includes

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

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 emitted 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 emitted 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. You can also call gdk_pixbuf_loader_get_pixbuf() later and get the same pixbuf.

The last signal, “area-updated”, gets emitted 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 updated area. 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 a GdkPixbufAnimationIter for displaying it.

Functions

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.

The list of supported image formats depends on what image loaders are installed, but typically "png", "jpeg", "gif", "tiff" and "xpm" are among the supported formats. To obtain the full list of supported image formats, call gdk_pixbuf_format_get_name() on each of the GdkPixbufFormat structs returned by gdk_pixbuf_get_formats().

Parameters

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.

[allow-none]

Returns

A newly-created pixbuf loader.


gdk_pixbuf_loader_new_with_mime_type ()

GdkPixbufLoader *
gdk_pixbuf_loader_new_with_mime_type (const char *mime_type,
                                      GError **error);

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

The list of supported mime types depends on what image loaders are installed, but typically "image/png", "image/jpeg", "image/gif", "image/tiff" and "image/x-xpixmap" are among the supported mime types. To obtain the full list of supported mime types, call gdk_pixbuf_format_get_mime_types() on each of the GdkPixbufFormat structs returned by gdk_pixbuf_get_formats().

Parameters

mime_type

the mime type to be loaded

 

error

return location for an allocated GError, or NULL to ignore errors.

[allow-none]

Returns

A newly-created pixbuf loader.

Since: 2.4


gdk_pixbuf_loader_get_format ()

GdkPixbufFormat *
gdk_pixbuf_loader_get_format (GdkPixbufLoader *loader);

Obtains the available information about the format of the currently loading image file.

Parameters

loader

A pixbuf loader.

 

Returns

A GdkPixbufFormat or NULL. The return value is owned by GdkPixbuf and should not be freed.

[nullable][transfer none]

Since: 2.2


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.

Parameters

loader

A pixbuf loader.

 

buf

Pointer to image data.

[array length=count]

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_write_bytes ()

gboolean
gdk_pixbuf_loader_write_bytes (GdkPixbufLoader *loader,
                               GBytes *buffer,
                               GError **error);

This will cause a pixbuf loader to parse a buffer inside a GBytes for 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.

See also: gdk_pixbuf_loader_write()

Parameters

loader

A pixbuf loader.

 

buffer

The image data as a GBytes

 

error

return location for errors

 

Returns

TRUE if the write was successful, or FALSE if the loader cannot parse the buffer.

Since: 2.30


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.

Parameters

loader

A pixbuf loader.

 

width

The desired width of the image being loaded.

 

height

The desired height of the image being loaded.

 

Since: 2.2


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()).

Parameters

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.

[transfer none]


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.

Parameters

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.

[transfer none]


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.

Remember that this does not unref the loader, so if you plan not to use it anymore, please g_object_unref() it.

Parameters

loader

A pixbuf loader.

 

error

return location for a GError, or NULL to ignore errors.

[allow-none]

Returns

TRUE if all image data written so far was successfully passed out via the update_area signal

Types and Values

struct GdkPixbufLoader

struct GdkPixbufLoader;

The GdkPixbufLoader struct contains only private fields.

Signal Details

The “area-prepared” signal

void
user_function (GdkPixbufLoader *loader,
               gpointer         user_data)

This signal is emitted when the pixbuf loader has allocated the pixbuf in the desired size. After this signal is emitted, applications can call gdk_pixbuf_loader_get_pixbuf() to fetch the partially-loaded pixbuf.

Parameters

loader

the object which received the signal.

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last


The “area-updated” signal

void
user_function (GdkPixbufLoader *loader,
               gint             x,
               gint             y,
               gint             width,
               gint             height,
               gpointer         user_data)

This signal is emitted when a significant area of the image being loaded has been updated. Normally it means that a complete scanline has been read in, but it could be a different area as well. Applications can use this signal to know when to repaint areas of an image that is being loaded.

Parameters

loader

the object which received the signal.

 

x

X offset of upper-left corner of the updated area.

 

y

Y offset of upper-left corner of the updated area.

 

width

Width of updated area.

 

height

Height of updated area.

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last


The “closed” signal

void
user_function (GdkPixbufLoader *loader,
               gpointer         user_data)

This signal is emitted when gdk_pixbuf_loader_close() is called. It can be used by different parts of an application to receive notification when an image loader is closed by the code that drives it.

Parameters

loader

the object which received the signal.

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last


The “size-prepared” signal

void
user_function (GdkPixbufLoader *loader,
               gint             width,
               gint             height,
               gpointer         user_data)

This signal is emitted when the pixbuf loader has been fed the initial amount of data that is required to figure out the size of the image that it will create. Applications can call gdk_pixbuf_loader_set_size() in response to this signal to set the desired size to which the image should be scaled.

Parameters

loader

the object which received the signal.

 

width

the original width of the image

 

height

the original height of the image

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last

See Also

gdk_pixbuf_new_from_file(), gdk_pixbuf_animation_new_from_file()

© manpagez.com 2000-2017
Individual documents may contain additional copyright information.