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Raster Sources

Raster Sources — Supplying arbitrary image data

Description

The raster source provides the ability to supply arbitrary pixel data whilst rendering. The pixels are queried at the time of rasterisation by means of user callback functions, allowing for the ultimate flexibility. For example, in handling compressed image sources, you may keep a MRU cache of decompressed images and decompress sources on the fly and discard old ones to conserve memory.

For the raster source to be effective, you must at least specify the acquire and release callbacks which are used to retrieve the pixel data for the region of interest and demark when it can be freed afterwards. Other callbacks are provided for when the pattern is copied temporarily during rasterisation, or more permanently as a snapshot in order to keep the pixel data available for printing.

Functions

cairo_pattern_create_raster_source ()

cairo_pattern_t *
cairo_pattern_create_raster_source (void *user_data,
                                    cairo_content_t content,
                                    int width,
                                    int height);

Creates a new user pattern for providing pixel data.

Use the setter functions to associate callbacks with the returned pattern. The only mandatory callback is acquire.

Parameters

user_data

the user data to be passed to all callbacks

 

content

content type for the pixel data that will be returned. Knowing the content type ahead of time is used for analysing the operation and picking the appropriate rendering path.

 

width

maximum size of the sample area

 

height

maximum size of the sample area

 

Returns

a newly created cairo_pattern_t. Free with cairo_pattern_destroy() when you are done using it.

Since: 1.12


cairo_raster_source_pattern_set_callback_data ()

void
cairo_raster_source_pattern_set_callback_data
                               (cairo_pattern_t *pattern,
                                void *data);

Updates the user data that is provided to all callbacks.

Parameters

pattern

the pattern to update

 

data

the user data to be passed to all callbacks

 

Since: 1.12


cairo_raster_source_pattern_get_callback_data ()

void *
cairo_raster_source_pattern_get_callback_data
                               (cairo_pattern_t *pattern);

Queries the current user data.

Parameters

pattern

the pattern to update

 

Returns

the current user-data passed to each callback

Since: 1.12


cairo_raster_source_pattern_set_acquire ()

void
cairo_raster_source_pattern_set_acquire
                               (cairo_pattern_t *pattern,
                                cairo_raster_source_acquire_func_t acquire,
                                cairo_raster_source_release_func_t release);

Specifies the callbacks used to generate the image surface for a rendering operation (acquire) and the function used to cleanup that surface afterwards.

The acquire callback should create a surface (preferably an image surface created to match the target using cairo_surface_create_similar_image()) that defines at least the region of interest specified by extents. The surface is allowed to be the entire sample area, but if it does contain a subsection of the sample area, the surface extents should be provided by setting the device offset (along with its width and height) using cairo_surface_set_device_offset().

Parameters

pattern

the pattern to update

 

acquire

acquire callback

 

release

release callback

 

Since: 1.12


cairo_raster_source_pattern_get_acquire ()

void
cairo_raster_source_pattern_get_acquire
                               (cairo_pattern_t *pattern,
                                cairo_raster_source_acquire_func_t *acquire,
                                cairo_raster_source_release_func_t *release);

Queries the current acquire and release callbacks.

Parameters

pattern

the pattern to query

 

acquire

return value for the current acquire callback

 

release

return value for the current release callback

 

Since: 1.12


cairo_raster_source_pattern_set_snapshot ()

void
cairo_raster_source_pattern_set_snapshot
                               (cairo_pattern_t *pattern,
                                cairo_raster_source_snapshot_func_t snapshot);

Sets the callback that will be used whenever a snapshot is taken of the pattern, that is whenever the current contents of the pattern should be preserved for later use. This is typically invoked whilst printing.

Parameters

pattern

the pattern to update

 

snapshot

snapshot callback

 

Since: 1.12


cairo_raster_source_pattern_get_snapshot ()

cairo_raster_source_snapshot_func_t
cairo_raster_source_pattern_get_snapshot
                               (cairo_pattern_t *pattern);

Queries the current snapshot callback.

Parameters

pattern

the pattern to query

 

Returns

the current snapshot callback

Since: 1.12


cairo_raster_source_pattern_set_copy ()

void
cairo_raster_source_pattern_set_copy (cairo_pattern_t *pattern,
                                      cairo_raster_source_copy_func_t copy);

Updates the copy callback which is used whenever a temporary copy of the pattern is taken.

Parameters

pattern

the pattern to update

 

copy

the copy callback

 

Since: 1.12


cairo_raster_source_pattern_get_copy ()

cairo_raster_source_copy_func_t
cairo_raster_source_pattern_get_copy (cairo_pattern_t *pattern);

Queries the current copy callback.

Parameters

pattern

the pattern to query

 

Returns

the current copy callback

Since: 1.12


cairo_raster_source_pattern_set_finish ()

void
cairo_raster_source_pattern_set_finish
                               (cairo_pattern_t *pattern,
                                cairo_raster_source_finish_func_t finish);

Updates the finish callback which is used whenever a pattern (or a copy thereof) will no longer be used.

Parameters

pattern

the pattern to update

 

finish

the finish callback

 

Since: 1.12


cairo_raster_source_pattern_get_finish ()

cairo_raster_source_finish_func_t
cairo_raster_source_pattern_get_finish
                               (cairo_pattern_t *pattern);

Queries the current finish callback.

Parameters

pattern

the pattern to query

 

Returns

the current finish callback

Since: 1.12


cairo_raster_source_acquire_func_t ()

cairo_surface_t
(*cairo_raster_source_acquire_func_t) (cairo_pattern_t *pattern,
                                       void *callback_data,
                                       cairo_surface_t *target,
                                       const cairo_rectangle_int_t *extents);

cairo_raster_source_acquire_func_t is the type of function which is called when a pattern is being rendered from. It should create a surface that provides the pixel data for the region of interest as defined by extents, though the surface itself does not have to be limited to that area. For convenience the surface should probably be of image type, created with cairo_surface_create_similar_image() for the target (which enables the number of copies to be reduced during transfer to the device). Another option, might be to return a similar surface to the target for explicit handling by the application of a set of cached sources on the device. The region of sample data provided should be defined using cairo_surface_set_device_offset() to specify the top-left corner of the sample data (along with width and height of the surface).

Parameters

pattern

the pattern being rendered from

 

callback_data

the user data supplied during creation

 

target

the rendering target surface

 

extents

rectangular region of interest in pixels in sample space

 

Returns

a cairo_surface_t

Since: 1.12


cairo_raster_source_release_func_t ()

void
(*cairo_raster_source_release_func_t) (cairo_pattern_t *pattern,
                                       void *callback_data,
                                       cairo_surface_t *surface);

cairo_raster_source_release_func_t is the type of function which is called when the pixel data is no longer being access by the pattern for the rendering operation. Typically this function will simply destroy the surface created during acquire.

Parameters

pattern

the pattern being rendered from

 

callback_data

the user data supplied during creation

 

surface

the surface created during acquire

 

Since: 1.12


cairo_raster_source_snapshot_func_t ()

cairo_status_t
(*cairo_raster_source_snapshot_func_t)
                               (cairo_pattern_t *pattern,
                                void *callback_data);

cairo_raster_source_snapshot_func_t is the type of function which is called when the pixel data needs to be preserved for later use during printing. This pattern will be accessed again later, and it is expected to provide the pixel data that was current at the time of snapshotting.

Parameters

pattern

the pattern being rendered from

 

callback_data

the user data supplied during creation

 

Returns

CAIRO_STATUS_SUCCESS on success, or one of the cairo_status_t error codes for failure.

Since: 1.12


cairo_raster_source_copy_func_t ()

cairo_status_t
(*cairo_raster_source_copy_func_t) (cairo_pattern_t *pattern,
                                    void *callback_data,
                                    const cairo_pattern_t *other);

cairo_raster_source_copy_func_t is the type of function which is called when the pattern gets copied as a normal part of rendering.

Parameters

pattern

the cairo_pattern_t that was copied to

 

callback_data

the user data supplied during creation

 

other

the cairo_pattern_t being used as the source for the copy

 

Returns

CAIRO_STATUS_SUCCESS on success, or one of the cairo_status_t error codes for failure.

Since: 1.12


cairo_raster_source_finish_func_t ()

void
(*cairo_raster_source_finish_func_t) (cairo_pattern_t *pattern,
                                      void *callback_data);

cairo_raster_source_finish_func_t is the type of function which is called when the pattern (or a copy thereof) is no longer required.

Parameters

pattern

the pattern being rendered from

 

callback_data

the user data supplied during creation

 

Since: 1.12

Types and Values

See Also

cairo_pattern_t

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