PNG Support

PNG Support — Reading and writing PNG images

Functions

Types and Values

Object Hierarchy


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.

Parameters

filename

name of PNG file to load

 

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

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

 

Returns

the status code of the read operation

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 read_func .

 

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

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

 

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.

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

 

Returns

the status code of the write operation

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

a cairo_write_func_t

 

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.

Since 1.0

Types and Values

CAIRO_HAS_PNG_FUNCTIONS

#define CAIRO_HAS_PNG_FUNCTIONS 1

Defined if the PNG functions are available. This macro can be used to conditionally compile code using the cairo PNG functions.

Since 1.0

See Also

cairo_surface_t