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35 GdkPixbufLoader

Application-driven progressive image loading.

35.1 Overview

<gdk-pixbuf-loader> 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 <gdk-pixbuf-loader> 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.

35.2 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 <gdk-pixbuf-animation> struct and gdk-pixbuf-animation-get-iter to get an <gdk-pixbuf-animation-iter> for displaying it.

35.3 Usage

— Class: <gdk-pixbuf-loader>

Derives from <gobject>.

This class defines no direct slots.

— Signal on <gdk-pixbuf-loader>: closed

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.

— Signal on <gdk-pixbuf-loader>: size-prepared (arg0 <gint>) (arg1 <gint>)

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.

— Signal on <gdk-pixbuf-loader>: area-prepared

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.

— Signal on <gdk-pixbuf-loader>: area-updated (arg0 <gint>) (arg1 <gint>) (arg2 <gint>) (arg3 <gint>)

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.

— Function: gdk-pixbuf-loader-new ⇒  (ret <gdk-pixbuf-loader>)

Creates a new pixbuf loader object.

ret
A newly-created pixbuf loader.
— Function: gdk-pixbuf-loader-new-with-type (image_type mchars) ⇒  (ret <gdk-pixbuf-loader>)

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 <gdk-pixbuf-format> structs returned by gdk-pixbuf-get-formats.

image-type
name of the image format to be loaded with the image
error
return location for an allocated <g-error>, or ‘#f’ to ignore errors
ret
A newly-created pixbuf loader.
— Function: gdk-pixbuf-loader-get-format (self <gdk-pixbuf-loader>) ⇒  (ret <gdk-pixbuf-format*>)
— Method: get-format

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

loader
A pixbuf loader.
ret
A <gdk-pixbuf-format> or ‘#f’. The return value is owned by GdkPixbuf and should not be freed.

Since 2.2

— Function: gdk-pixbuf-loader-set-size (self <gdk-pixbuf-loader>) (width int) (height int)
— Method: set-size

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.

Since 2.2

— Function: gdk-pixbuf-loader-get-pixbuf (self <gdk-pixbuf-loader>) ⇒  (ret <gdk-pixbuf>)
— Method: get-pixbuf

Queries the <gdk-pixbuf> 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 ‘#f’. 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.
ret
The <gdk-pixbuf> that the loader is creating, or ‘#f’ if not enough data has been read to determine how to create the image buffer.
— Function: gdk-pixbuf-loader-get-animation (self <gdk-pixbuf-loader>) ⇒  (ret <gdk-pixbuf-animation>)
— Method: get-animation

Queries the <gdk-pixbuf-animation> 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 ‘#f’.

loader
A pixbuf loader
ret
The <gdk-pixbuf-animation> that the loader is loading, or ‘#f’ if not enough data has been read to determine the information.
— Function: gdk-pixbuf-loader-close (self <gdk-pixbuf-loader>) ⇒  (ret bool)
— Method: close

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 ‘#f’ 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 ‘#f’ for error to ignore it is reasonable.

loader
A pixbuf loader.
error
return location for a <g-error>, or ‘#f’ to ignore errors
ret
‘#t’ if all image data written so far was successfully passed out via the update_area signal