beta-0.89.2

[luatex.git] / source / libs / cairo / cairo-src / src / cairo-png.c

/* cairo - a vector graphics library with display and print output
 *
 * Copyright © 2003 University of Southern California
 *
 * This library is free software; you can redistribute it and/or
 * modify it either under the terms of the GNU Lesser General Public
 * License version 2.1 as published by the Free Software Foundation
 * (the "LGPL") or, at your option, under the terms of the Mozilla
 * Public License Version 1.1 (the "MPL"). If you do not alter this
 * notice, a recipient may use your version of this file under either
 * the MPL or the LGPL.
 *
 * You should have received a copy of the LGPL along with this library
 * in the file COPYING-LGPL-2.1; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA
 * You should have received a copy of the MPL along with this library
 * in the file COPYING-MPL-1.1
 *
 * The contents of this file are subject to the Mozilla Public License
 * Version 1.1 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
 * OF ANY KIND, either express or implied. See the LGPL or the MPL for
 * the specific language governing rights and limitations.
 *
 * The Original Code is the cairo graphics library.
 *
 * The Initial Developer of the Original Code is University of Southern
 * California.
 *
 * Contributor(s):
 *      Carl D. Worth <cworth@cworth.org>
 *      Kristian Høgsberg <krh@redhat.com>
 *      Chris Wilson <chris@chris-wilson.co.uk>
 */

#include "cairoint.h"

#include "cairo-error-private.h"
#include "cairo-image-surface-private.h"
#include "cairo-output-stream-private.h"

#include <stdio.h>
#include <errno.h>
#include <png.h>

/**
 * SECTION:cairo-png
 * @Title: PNG Support
 * @Short_Description: Reading and writing PNG images
 * @See_Also: #cairo_surface_t
 *
 * 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.
 **/

/**
 * CAIRO_HAS_PNG_FUNCTIONS:
 *
 * Defined if the PNG functions are available.
 * This macro can be used to conditionally compile code using the cairo
 * PNG functions.
 *
 * Since: 1.0
 **/

struct png_read_closure_t {
    cairo_read_func_t            read_func;
    void                        *closure;
    cairo_output_stream_t       *png_data;
};


/* Unpremultiplies data and converts native endian ARGB => RGBA bytes */
static void
unpremultiply_data (png_structp png, png_row_infop row_info, png_bytep data)
{
    unsigned int i;

    for (i = 0; i < row_info->rowbytes; i += 4) {
        uint8_t *b = &data[i];
        uint32_t pixel;
        uint8_t  alpha;

        memcpy (&pixel, b, sizeof (uint32_t));
        alpha = (pixel & 0xff000000) >> 24;
        if (alpha == 0) {
            b[0] = b[1] = b[2] = b[3] = 0;
        } else {
            b[0] = (((pixel & 0xff0000) >> 16) * 255 + alpha / 2) / alpha;
            b[1] = (((pixel & 0x00ff00) >>  8) * 255 + alpha / 2) / alpha;
            b[2] = (((pixel & 0x0000ff) >>  0) * 255 + alpha / 2) / alpha;
            b[3] = alpha;
        }
    }
}

/* Converts native endian xRGB => RGBx bytes */
static void
convert_data_to_bytes (png_structp png, png_row_infop row_info, png_bytep data)
{
    unsigned int i;

    for (i = 0; i < row_info->rowbytes; i += 4) {
        uint8_t *b = &data[i];
        uint32_t pixel;

        memcpy (&pixel, b, sizeof (uint32_t));

        b[0] = (pixel & 0xff0000) >> 16;
        b[1] = (pixel & 0x00ff00) >>  8;
        b[2] = (pixel & 0x0000ff) >>  0;
        b[3] = 0;
    }
}

/* Use a couple of simple error callbacks that do not print anything to
 * stderr and rely on the user to check for errors via the #cairo_status_t
 * return.
 */
static void
png_simple_error_callback (png_structp png,
                           png_const_charp error_msg)
{
    cairo_status_t *error = png_get_error_ptr (png);

    /* default to the most likely error */
    if (*error == CAIRO_STATUS_SUCCESS)
        *error = _cairo_error (CAIRO_STATUS_NO_MEMORY);

#ifdef PNG_SETJMP_SUPPORTED
    longjmp (png_jmpbuf (png), 1);
#endif

    /* if we get here, then we have to choice but to abort ... */
}

static void
png_simple_warning_callback (png_structp png,
                             png_const_charp error_msg)
{
    /* png does not expect to abort and will try to tidy up and continue
     * loading the image after a warning. So we also want to return the
     * (incorrect?) surface.
     *
     * We use our own warning callback to squelch any attempts by libpng
     * to write to stderr as we may not be in control of that output.
     */
}


/* Starting with libpng-1.2.30, we must explicitly specify an output_flush_fn.
 * Otherwise, we will segfault if we are writing to a stream. */
static void
png_simple_output_flush_fn (png_structp png_ptr)
{
}

static cairo_status_t
write_png (cairo_surface_t      *surface,
           png_rw_ptr           write_func,
           void                 *closure)
{
    int i;
    cairo_int_status_t status;
    cairo_image_surface_t *image;
    cairo_image_surface_t * volatile clone;
    void *image_extra;
    png_struct *png;
    png_info *info;
    png_byte **volatile rows = NULL;
    png_color_16 white;
    int png_color_type;
    int bpc;

    status = _cairo_surface_acquire_source_image (surface,
                                                  &image,
                                                  &image_extra);

    if (status == CAIRO_INT_STATUS_UNSUPPORTED)
        return _cairo_error (CAIRO_STATUS_SURFACE_TYPE_MISMATCH);
    else if (unlikely (status))
        return status;

    /* PNG complains about "Image width or height is zero in IHDR" */
    if (image->width == 0 || image->height == 0) {
        status = _cairo_error (CAIRO_STATUS_WRITE_ERROR);
        goto BAIL1;
    }

    /* Handle the various fallback formats (e.g. low bit-depth XServers)
     * by coercing them to a simpler format using pixman.
     */
    clone = _cairo_image_surface_coerce (image);
    status = clone->base.status;
    if (unlikely (status))
        goto BAIL1;

    rows = _cairo_malloc_ab (clone->height, sizeof (png_byte*));
    if (unlikely (rows == NULL)) {
        status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
        goto BAIL2;
    }

    for (i = 0; i < clone->height; i++)
        rows[i] = (png_byte *) clone->data + i * clone->stride;

    png = png_create_write_struct (PNG_LIBPNG_VER_STRING, &status,
                                   png_simple_error_callback,
                                   png_simple_warning_callback);
    if (unlikely (png == NULL)) {
        status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
        goto BAIL3;
    }

    info = png_create_info_struct (png);
    if (unlikely (info == NULL)) {
        status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
        goto BAIL4;
    }

#ifdef PNG_SETJMP_SUPPORTED
    if (setjmp (png_jmpbuf (png)))
        goto BAIL4;
#endif

    png_set_write_fn (png, closure, write_func, png_simple_output_flush_fn);

    switch (clone->format) {
    case CAIRO_FORMAT_ARGB32:
        bpc = 8;
        if (_cairo_image_analyze_transparency (clone) == CAIRO_IMAGE_IS_OPAQUE)
            png_color_type = PNG_COLOR_TYPE_RGB;
        else
            png_color_type = PNG_COLOR_TYPE_RGB_ALPHA;
        break;
    case CAIRO_FORMAT_RGB30:
        bpc = 10;
        png_color_type = PNG_COLOR_TYPE_RGB;
        break;
    case CAIRO_FORMAT_RGB24:
        bpc = 8;
        png_color_type = PNG_COLOR_TYPE_RGB;
        break;
    case CAIRO_FORMAT_A8:
        bpc = 8;
        png_color_type = PNG_COLOR_TYPE_GRAY;
        break;
    case CAIRO_FORMAT_A1:
        bpc = 1;
        png_color_type = PNG_COLOR_TYPE_GRAY;
#ifndef WORDS_BIGENDIAN
        png_set_packswap (png);
#endif
        break;
    case CAIRO_FORMAT_INVALID:
    case CAIRO_FORMAT_RGB16_565:
    default:
        status = _cairo_error (CAIRO_STATUS_INVALID_FORMAT);
        goto BAIL4;
    }

    png_set_IHDR (png, info,
                  clone->width,
                  clone->height, bpc,
                  png_color_type,
                  PNG_INTERLACE_NONE,
                  PNG_COMPRESSION_TYPE_DEFAULT,
                  PNG_FILTER_TYPE_DEFAULT);

    white.gray = (1 << bpc) - 1;
    white.red = white.blue = white.green = white.gray;
    png_set_bKGD (png, info, &white);

    if (0) { /* XXX extract meta-data from surface (i.e. creation date) */
        png_time pt;

        png_convert_from_time_t (&pt, time (NULL));
        png_set_tIME (png, info, &pt);
    }

    /* We have to call png_write_info() before setting up the write
     * transformation, since it stores data internally in 'png'
     * that is needed for the write transformation functions to work.
     */
    png_write_info (png, info);

    if (png_color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
        png_set_write_user_transform_fn (png, unpremultiply_data);
    } else if (png_color_type == PNG_COLOR_TYPE_RGB) {
        png_set_write_user_transform_fn (png, convert_data_to_bytes);
        png_set_filler (png, 0, PNG_FILLER_AFTER);
    }

    png_write_image (png, rows);
    png_write_end (png, info);

BAIL4:
    png_destroy_write_struct (&png, &info);
BAIL3:
    free (rows);
BAIL2:
    cairo_surface_destroy (&clone->base);
BAIL1:
    _cairo_surface_release_source_image (surface, image, image_extra);

    return status;
}

static void
stdio_write_func (png_structp png, png_bytep data, png_size_t size)
{
    FILE *fp;

    fp = png_get_io_ptr (png);
    while (size) {
        size_t ret = fwrite (data, 1, size, fp);
        size -= ret;
        data += ret;
        if (size && ferror (fp)) {
            cairo_status_t *error = png_get_error_ptr (png);
            if (*error == CAIRO_STATUS_SUCCESS)
                *error = _cairo_error (CAIRO_STATUS_WRITE_ERROR);
            png_error (png, NULL);
        }
    }
}

/**
 * cairo_surface_write_to_png:
 * @surface: a #cairo_surface_t with pixel contents
 * @filename: the name of a file to write to
 *
 * Writes the contents of @surface to a new file @filename as a PNG
 * image.
 *
 * Return value: %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_status_t
cairo_surface_write_to_png (cairo_surface_t     *surface,
                            const char          *filename)
{
    FILE *fp;
    cairo_status_t status;

    if (surface->status)
        return surface->status;

    if (surface->finished)
        return _cairo_error (CAIRO_STATUS_SURFACE_FINISHED);

    fp = fopen (filename, "wb");
    if (fp == NULL) {
        switch (errno) {
        case ENOMEM:
            return _cairo_error (CAIRO_STATUS_NO_MEMORY);
        default:
            return _cairo_error (CAIRO_STATUS_WRITE_ERROR);
        }
    }

    status = write_png (surface, stdio_write_func, fp);

    if (fclose (fp) && status == CAIRO_STATUS_SUCCESS)
        status = _cairo_error (CAIRO_STATUS_WRITE_ERROR);

    return status;
}

struct png_write_closure_t {
    cairo_write_func_t           write_func;
    void                        *closure;
};

static void
stream_write_func (png_structp png, png_bytep data, png_size_t size)
{
    cairo_status_t status;
    struct png_write_closure_t *png_closure;

    png_closure = png_get_io_ptr (png);
    status = png_closure->write_func (png_closure->closure, data, size);
    if (unlikely (status)) {
        cairo_status_t *error = png_get_error_ptr (png);
        if (*error == CAIRO_STATUS_SUCCESS)
            *error = status;
        png_error (png, NULL);
    }
}

/**
 * cairo_surface_write_to_png_stream:
 * @surface: a #cairo_surface_t with pixel contents
 * @write_func: a #cairo_write_func_t
 * @closure: closure data for the write function
 *
 * Writes the image surface to the write function.
 *
 * Return value: %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
 **/
cairo_status_t
cairo_surface_write_to_png_stream (cairo_surface_t      *surface,
                                   cairo_write_func_t   write_func,
                                   void                 *closure)
{
    struct png_write_closure_t png_closure;

    if (surface->status)
        return surface->status;

    if (surface->finished)
        return _cairo_error (CAIRO_STATUS_SURFACE_FINISHED);

    png_closure.write_func = write_func;
    png_closure.closure = closure;

    return write_png (surface, stream_write_func, &png_closure);
}
slim_hidden_def (cairo_surface_write_to_png_stream);

static inline int
multiply_alpha (int alpha, int color)
{
    int temp = (alpha * color) + 0x80;
    return ((temp + (temp >> 8)) >> 8);
}

/* Premultiplies data and converts RGBA bytes => native endian */
static void
premultiply_data (png_structp   png,
                  png_row_infop row_info,
                  png_bytep     data)
{
    unsigned int i;

    for (i = 0; i < row_info->rowbytes; i += 4) {
        uint8_t *base  = &data[i];
        uint8_t  alpha = base[3];
        uint32_t p;

        if (alpha == 0) {
            p = 0;
        } else {
            uint8_t  red   = base[0];
            uint8_t  green = base[1];
            uint8_t  blue  = base[2];

            if (alpha != 0xff) {
                red   = multiply_alpha (alpha, red);
                green = multiply_alpha (alpha, green);
                blue  = multiply_alpha (alpha, blue);
            }
            p = (alpha << 24) | (red << 16) | (green << 8) | (blue << 0);
        }
        memcpy (base, &p, sizeof (uint32_t));
    }
}

/* Converts RGBx bytes to native endian xRGB */
static void
convert_bytes_to_data (png_structp png, png_row_infop row_info, png_bytep data)
{
    unsigned int i;

    for (i = 0; i < row_info->rowbytes; i += 4) {
        uint8_t *base  = &data[i];
        uint8_t  red   = base[0];
        uint8_t  green = base[1];
        uint8_t  blue  = base[2];
        uint32_t pixel;

        pixel = (0xff << 24) | (red << 16) | (green << 8) | (blue << 0);
        memcpy (base, &pixel, sizeof (uint32_t));
    }
}

static cairo_status_t
stdio_read_func (void *closure, unsigned char *data, unsigned int size)
{
    FILE *file = closure;

    while (size) {
        size_t ret;

        ret = fread (data, 1, size, file);
        size -= ret;
        data += ret;

        if (size && (feof (file) || ferror (file)))
            return _cairo_error (CAIRO_STATUS_READ_ERROR);
    }

    return CAIRO_STATUS_SUCCESS;
}

static void
stream_read_func (png_structp png, png_bytep data, png_size_t size)
{
    cairo_status_t status;
    struct png_read_closure_t *png_closure;

    png_closure = png_get_io_ptr (png);
    status = png_closure->read_func (png_closure->closure, data, size);
    if (unlikely (status)) {
        cairo_status_t *error = png_get_error_ptr (png);
        if (*error == CAIRO_STATUS_SUCCESS)
            *error = status;
        png_error (png, NULL);
    }

    _cairo_output_stream_write (png_closure->png_data, data, size);
}

static cairo_surface_t *
read_png (struct png_read_closure_t *png_closure)
{
    cairo_surface_t *surface;
    png_struct *png = NULL;
    png_info *info;
    png_byte *data = NULL;
    png_byte **row_pointers = NULL;
    png_uint_32 png_width, png_height;
    int depth, color_type, interlace, stride;
    unsigned int i;
    cairo_format_t format;
    cairo_status_t status;
    unsigned char *mime_data;
    unsigned long mime_data_length;

    png_closure->png_data = _cairo_memory_stream_create ();

    /* XXX: Perhaps we'll want some other error handlers? */
    png = png_create_read_struct (PNG_LIBPNG_VER_STRING,
                                  &status,
                                  png_simple_error_callback,
                                  png_simple_warning_callback);
    if (unlikely (png == NULL)) {
        surface = _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_NO_MEMORY));
        goto BAIL;
    }

    info = png_create_info_struct (png);
    if (unlikely (info == NULL)) {
        surface = _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_NO_MEMORY));
        goto BAIL;
    }

    png_set_read_fn (png, png_closure, stream_read_func);

    status = CAIRO_STATUS_SUCCESS;
#ifdef PNG_SETJMP_SUPPORTED
    if (setjmp (png_jmpbuf (png))) {
        surface = _cairo_surface_create_in_error (status);
        goto BAIL;
    }
#endif

    png_read_info (png, info);

    png_get_IHDR (png, info,
                  &png_width, &png_height, &depth,
                  &color_type, &interlace, NULL, NULL);
    if (unlikely (status)) { /* catch any early warnings */
        surface = _cairo_surface_create_in_error (status);
        goto BAIL;
    }

    /* convert palette/gray image to rgb */
    if (color_type == PNG_COLOR_TYPE_PALETTE)
        png_set_palette_to_rgb (png);

    /* expand gray bit depth if needed */
    if (color_type == PNG_COLOR_TYPE_GRAY) {
#if PNG_LIBPNG_VER >= 10209
        png_set_expand_gray_1_2_4_to_8 (png);
#else
        png_set_gray_1_2_4_to_8 (png);
#endif
    }

    /* transform transparency to alpha */
    if (png_get_valid (png, info, PNG_INFO_tRNS))
        png_set_tRNS_to_alpha (png);

    if (depth == 16)
        png_set_strip_16 (png);

    if (depth < 8)
        png_set_packing (png);

    /* convert grayscale to RGB */
    if (color_type == PNG_COLOR_TYPE_GRAY ||
        color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
    {
        png_set_gray_to_rgb (png);
    }

    if (interlace != PNG_INTERLACE_NONE)
        png_set_interlace_handling (png);

    png_set_filler (png, 0xff, PNG_FILLER_AFTER);

    /* recheck header after setting EXPAND options */
    png_read_update_info (png, info);
    png_get_IHDR (png, info,
                  &png_width, &png_height, &depth,
                  &color_type, &interlace, NULL, NULL);
    if (depth != 8 ||
        ! (color_type == PNG_COLOR_TYPE_RGB ||
           color_type == PNG_COLOR_TYPE_RGB_ALPHA))
    {
        surface = _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_READ_ERROR));
        goto BAIL;
    }

    switch (color_type) {
        default:
            ASSERT_NOT_REACHED;
            /* fall-through just in case ;-) */

        case PNG_COLOR_TYPE_RGB_ALPHA:
            format = CAIRO_FORMAT_ARGB32;
            png_set_read_user_transform_fn (png, premultiply_data);
            break;

        case PNG_COLOR_TYPE_RGB:
            format = CAIRO_FORMAT_RGB24;
            png_set_read_user_transform_fn (png, convert_bytes_to_data);
            break;
    }

    stride = cairo_format_stride_for_width (format, png_width);
    if (stride < 0) {
        surface = _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_INVALID_STRIDE));
        goto BAIL;
    }

    data = _cairo_malloc_ab (png_height, stride);
    if (unlikely (data == NULL)) {
        surface = _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_NO_MEMORY));
        goto BAIL;
    }

    row_pointers = _cairo_malloc_ab (png_height, sizeof (char *));
    if (unlikely (row_pointers == NULL)) {
        surface = _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_NO_MEMORY));
        goto BAIL;
    }

    for (i = 0; i < png_height; i++)
        row_pointers[i] = &data[i * stride];

    png_read_image (png, row_pointers);
    png_read_end (png, info);

    if (unlikely (status)) { /* catch any late warnings - probably hit an error already */
        surface = _cairo_surface_create_in_error (status);
        goto BAIL;
    }

    surface = cairo_image_surface_create_for_data (data, format,
                                                   png_width, png_height,
                                                   stride);
    if (surface->status)
        goto BAIL;

    _cairo_image_surface_assume_ownership_of_data ((cairo_image_surface_t*)surface);
    data = NULL;

    _cairo_debug_check_image_surface_is_defined (surface);

    status = _cairo_memory_stream_destroy (png_closure->png_data,
                                           &mime_data,
                                           &mime_data_length);
    png_closure->png_data = NULL;
    if (unlikely (status)) {
        cairo_surface_destroy (surface);
        surface = _cairo_surface_create_in_error (status);
        goto BAIL;
    }

    status = cairo_surface_set_mime_data (surface,
                                          CAIRO_MIME_TYPE_PNG,
                                          mime_data,
                                          mime_data_length,
                                          free,
                                          mime_data);
    if (unlikely (status)) {
        free (mime_data);
        cairo_surface_destroy (surface);
        surface = _cairo_surface_create_in_error (status);
        goto BAIL;
    }

 BAIL:
    free (row_pointers);
    free (data);
    if (png != NULL)
        png_destroy_read_struct (&png, &info, NULL);
    if (png_closure->png_data != NULL) {
        cairo_status_t status_ignored;

        status_ignored = _cairo_output_stream_destroy (png_closure->png_data);
    }

    return surface;
}

/**
 * cairo_image_surface_create_from_png:
 * @filename: name of PNG file to load
 *
 * Creates a new image surface and initializes the contents to the
 * given PNG file.
 *
 * Return value: 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_surface_t *
cairo_image_surface_create_from_png (const char *filename)
{
    struct png_read_closure_t png_closure;
    cairo_surface_t *surface;

    png_closure.closure = fopen (filename, "rb");
    if (png_closure.closure == NULL) {
        cairo_status_t status;
        switch (errno) {
        case ENOMEM:
            status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
            break;
        case ENOENT:
            status = _cairo_error (CAIRO_STATUS_FILE_NOT_FOUND);
            break;
        default:
            status = _cairo_error (CAIRO_STATUS_READ_ERROR);
            break;
        }
        return _cairo_surface_create_in_error (status);
    }

    png_closure.read_func = stdio_read_func;

    surface = read_png (&png_closure);

    fclose (png_closure.closure);

    return surface;
}

/**
 * cairo_image_surface_create_from_png_stream:
 * @read_func: function called to read the data of the file
 * @closure: data to pass to @read_func.
 *
 * Creates a new image surface from PNG data read incrementally
 * via the @read_func function.
 *
 * Return value: 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_t *
cairo_image_surface_create_from_png_stream (cairo_read_func_t   read_func,
                                            void                *closure)
{
    struct png_read_closure_t png_closure;

    png_closure.read_func = read_func;
    png_closure.closure = closure;

    return read_png (&png_closure);
}