The gdk-pixbuf Library
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# GdkPixbufLoader

## Name

GdkPixbufLoader -- Application-driven progressive image loading.

## Synopsis

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

    #define     GDK_PIXBUF_LOADER               (obj)
    GdkPixbufLoader* gdk_pixbuf_loader_new      (void);
    gboolean    gdk_pixbuf_loader_write         (GdkPixbufLoader *loader,
                                                 const guchar *buf,
                                                 size_t count);
    GdkPixbuf*  gdk_pixbuf_loader_get_pixbuf    (GdkPixbufLoader *loader);
    GdkPixbufAnimation* gdk_pixbuf_loader_get_animation
                                                (GdkPixbufLoader *loader);
    void        gdk_pixbuf_loader_close         (GdkPixbufLoader *loader);

## Object Hierarchy

      GtkObject
       +----GdkPixbufLoader

## Signal Prototypes

    "area-updated"
                void        user_function      (GdkPixbufLoader *gdkpixbufloader,
                                                gint arg1,
                                                gint arg2,
                                                gint arg3,
                                                gint arg4,
                                                gpointer user_data);
    "area-prepared"
                void        user_function      (GdkPixbufLoader *gdkpixbufloader,
                                                gpointer user_data);
    "frame-done"
                void        user_function      (GdkPixbufLoader *gdkpixbufloader,
                                                gpointer arg1,
                                                gpointer user_data);
    "animation-done"
                void        user_function      (GdkPixbufLoader *gdkpixbufloader,
                                                gpointer user_data);
    "closed"    void        user_function      (GdkPixbufLoader *gdkpixbufloader,
                                                gpointer user_data);

## 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() 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 two important signals throughout the process. The first, "area_prepared", will be called as soon as the image has enough information to determine the size of the image to be used. It will pass a `GdkPixbuf` in. If you want to use it, you can 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 the gdk_pixbuf_loader_get_pixbuf() once this signal has been emitted and get the same pixbuf.

The other 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 a little more complex then loading an image. In addition to the above signals, there is also a "frame_done" signal, as well as an "animation_done" signal. The first lets the application know that it is dealing with an animation, instead of a static image. It also passes a GdkPixbufFrame in the signal. As before, if you want to keep the frame, you need to ref it. Once the first "frame_done" signal has been emitted, you can call gdk_pixbuf_loader_get_animation() to get the GdkPixbufAnimation struct. Each subsequent frame goes through a similar lifecycle. For example "area_prepared" is re-emitted. Then "area_updated" is emitted as many times as necessary. Finally, "animation_done" is emitted as soon as all frames are done.

## Details

### GDK_PIXBUF_LOADER()

    #define GDK_PIXBUF_LOADER(obj)		   (GTK_CHECK_CAST ((obj), GDK_TYPE_PIXBUF_LOADER, GdkPixbufLoader))

Casts a GtkObject to a GdkPixbufLoader.

`obj` : | A GTK+ object.

### 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_write ()

    gboolean    gdk_pixbuf_loader_write         (GdkPixbufLoader *loader,
                                                 const guchar *buf,
                                                 size_t count);

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.

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

### 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 afer 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 gdk_pixbuf_ref() should be sufficient to continue using it. Additionally, if the loader is an animation, it will return the first frame of the animation.

`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 afer the "area_prepared" signal has been emitted by the loader. If the image is not an animation, then it 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 ()

    void        gdk_pixbuf_loader_close         (GdkPixbufLoader *loader);

Informs a pixbuf loader that no further writes with gdk_pixbuf_load_write() will occur, so that it can free its internal loading structures.

`loader` : | A pixbuf loader.

## Signals

### The "area-updated" signal

    void        user_function                  (GdkPixbufLoader *gdkpixbufloader,
                                                gint arg1,
                                                gint arg2,
                                                gint arg3,
                                                gint arg4,
                                                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.

`loader` : | Loader which emitted 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.

### The "area-prepared" signal

    void        user_function                  (GdkPixbufLoader *gdkpixbufloader,
                                                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 and format of the image that it will create. After this signal is emitted, applications can call gdk_pixbuf_loader_get_pixbuf() to fetch the partially-loaded pixbuf.

`loader` : | Loader which emitted the signal.
`user_data` : | user data set when the signal handler was connected.

### The "frame-done" signal

    void        user_function                  (GdkPixbufLoader *gdkpixbufloader,
                                                gpointer arg1,
                                                gpointer user_data);

This signal is emitted when a frame is done loading. It will be emitted for each frame in an animation data stream.

`loader` : | Loader which emitted the signal.
`frame` : | Frame which just completed loading.
`user_data` : | user data set when the signal handler was connected.

### The "animation-done" signal

    void        user_function                  (GdkPixbufLoader *gdkpixbufloader,
                                                gpointer user_data);

This signal is emitted when an animation is done loading.

`loader` : | Loader which emitted the signal.
`user_data` : | user data set when the signal handler was connected.

### The "closed" signal

    void        user_function                  (GdkPixbufLoader *gdkpixbufloader,
                                                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.

`loader` : | Loader which emitted the signal.
`user_data` : | user data set when the signal handler was connected.

## See Also

gdk_pixbuf_new_from_file()

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