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Description
The PNG functions allow reading PNG images into image surfaces, and writing any surface to a PNG file.
It is a toy API. It only offers very simple support for reading and
writing PNG files, which is sufficient for testing and
demonstration purposes. Applications which need more control over
the generated PNG file should access the pixel data directly, using
cairo_image_surface_get_data() or a backend-specific access
function, and process it with another library, e.g. gdk-pixbuf or
libpng.
Functions
cairo_image_surface_create_from_png ()
cairo_surface_t *
cairo_image_surface_create_from_png (const char *filename);
Creates a new image surface and initializes the contents to the given PNG file.
Returns
a new cairo_surface_t initialized with the contents of the PNG file, or a "nil" surface if any error occurred. A nil surface can be checked for with cairo_surface_status(surface) which may return one of the following values:
CAIRO_STATUS_NO_MEMORY
CAIRO_STATUS_FILE_NOT_FOUND
CAIRO_STATUS_READ_ERROR
CAIRO_STATUS_PNG_ERROR
Alternatively, you can allow errors to propagate through the drawing
operations and check the status on the context upon completion
using cairo_status().
Since: 1.0
cairo_read_func_t ()
cairo_status_t (*cairo_read_func_t) (void *closure,unsigned char *data,unsigned int length);
cairo_read_func_t is the type of function which is called when a
backend needs to read data from an input stream. It is passed the
closure which was specified by the user at the time the read
function was registered, the buffer to read the data into and the
length of the data in bytes. The read function should return
CAIRO_STATUS_SUCCESS if all the data was successfully read,
CAIRO_STATUS_READ_ERROR otherwise.
Parameters
closure |
the input closure |
|
data |
the buffer into which to read the data |
|
length |
the amount of data to read |
Since: 1.0
cairo_image_surface_create_from_png_stream ()
cairo_surface_t * cairo_image_surface_create_from_png_stream (cairo_read_func_t read_func,void *closure);
Creates a new image surface from PNG data read incrementally
via the read_func
function.
Parameters
read_func |
function called to read the data of the file |
|
closure |
data to pass to |
Returns
a new cairo_surface_t initialized with the contents of the PNG file or a "nil" surface if the data read is not a valid PNG image or memory could not be allocated for the operation. A nil surface can be checked for with cairo_surface_status(surface) which may return one of the following values:
CAIRO_STATUS_NO_MEMORY
CAIRO_STATUS_READ_ERROR
CAIRO_STATUS_PNG_ERROR
Alternatively, you can allow errors to propagate through the drawing
operations and check the status on the context upon completion
using cairo_status().
Since: 1.0
cairo_surface_write_to_png ()
cairo_status_t cairo_surface_write_to_png (cairo_surface_t *surface,const char *filename);
Writes the contents of surface
to a new file filename
as a PNG
image.
Parameters
surface |
a cairo_surface_t with pixel contents |
|
filename |
the name of a file to write to; on Windows this filename is encoded in UTF-8. |
Returns
CAIRO_STATUS_SUCCESS if the PNG file was written
successfully. Otherwise, CAIRO_STATUS_NO_MEMORY if memory could not
be allocated for the operation or
CAIRO_STATUS_SURFACE_TYPE_MISMATCH if the surface does not have
pixel contents, or CAIRO_STATUS_WRITE_ERROR if an I/O error occurs
while attempting to write the file, or CAIRO_STATUS_PNG_ERROR if libpng
returned an error.
Since: 1.0
cairo_write_func_t ()
cairo_status_t (*cairo_write_func_t) (void *closure,const unsigned char *data,unsigned int length);
cairo_write_func_t is the type of function which is called when a
backend needs to write data to an output stream. It is passed the
closure which was specified by the user at the time the write
function was registered, the data to write and the length of the
data in bytes. The write function should return
CAIRO_STATUS_SUCCESS if all the data was successfully written,
CAIRO_STATUS_WRITE_ERROR otherwise.
Parameters
closure |
the output closure |
|
data |
the buffer containing the data to write |
|
length |
the amount of data to write |
Since: 1.0
cairo_surface_write_to_png_stream ()
cairo_status_t cairo_surface_write_to_png_stream (cairo_surface_t *surface,cairo_write_func_t write_func,void *closure);
Writes the image surface to the write function.
Parameters
surface |
a cairo_surface_t with pixel contents |
|
write_func |
||
closure |
closure data for the write function |
Returns
CAIRO_STATUS_SUCCESS if the PNG file was written
successfully. Otherwise, CAIRO_STATUS_NO_MEMORY is returned if
memory could not be allocated for the operation,
CAIRO_STATUS_SURFACE_TYPE_MISMATCH if the surface does not have
pixel contents, or CAIRO_STATUS_PNG_ERROR if libpng
returned an error.
Since: 1.0