Description
GdkPixbufLoader provides a way for applications to drive the
process of loading an image, by letting them send the image data
directly. 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.
gdk_pixbuf_loader_new ()
Creates a new pixbuf loader object.
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.
gdk_pixbuf_loader_get_pixbuf ()
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.
gdk_pixbuf_loader_get_animation ()
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.
gdk_pixbuf_loader_close ()
Informs a pixbuf loader that no further writes with gdk_pixbuf_load_write()
will occur, so that it can free its internal loading structures.
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.
The "area-prepared" signal
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.
The "animation-done" signal
The "closed" signal
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.