## PNG Support

PNG Support — Reading and writing PNG images

## Synopsis

    #define             CAIRO_HAS_PNG_FUNCTIONS
    cairo_surface_t *   cairo_image_surface_create_from_png (const char *filename);
    cairo_status_t      (*cairo_read_func_t)                (void *closure,
                                                             unsigned char *data,
                                                             unsigned int length);
    cairo_surface_t *   cairo_image_surface_create_from_png_stream
                                                            (cairo_read_func_t read_func,
                                                             void *closure);
    cairo_status_t      cairo_surface_write_to_png          (cairo_surface_t *surface,
                                                             const char *filename);
    cairo_status_t      (*cairo_write_func_t)               (void *closure,
                                                             unsigned char *data,
                                                             unsigned int length);
    cairo_status_t      cairo_surface_write_to_png_stream   (cairo_surface_t *surface,
                                                             cairo_write_func_t write_func,
                                                             void *closure);

## Description

The PNG functions allow reading PNG images into image surfaces, and writing any surface to a PNG file.

## Details

### 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.

### 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.

`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()`.

### 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.

`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

### 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.

`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()`.

### 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.

`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.

### cairo_write_func_t ()

    cairo_status_t      (*cairo_write_func_t)               (void *closure,
                                                             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.

`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

### 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.

`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.

## See Also

cairo_surface_t