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png-write.cpp

#define __SP_PNG_WRITE_C__

/*
 * PNG file format utilities
 *
 * Authors:
 *   Lauris Kaplinski <lauris@kaplinski.com>
 *   Whoever wrote this example in libpng documentation
 *
 * Copyright (C) 1999-2002 authors
 *
 * Released under GNU GPL, read the file 'COPYING' for more information
 */

#include "config.h"

#include <png.h>
#include <glib.h>
#include "png-write.h"
#include "io/sys.h"

/* This is an example of how to use libpng to read and write PNG files.
 * The file libpng.txt is much more verbose then this.  If you have not
 * read it, do so first.  This was designed to be a starting point of an
 * implementation.  This is not officially part of libpng, and therefore
 * does not require a copyright notice.
 *
 * This file does not currently compile, because it is missing certain
 * parts, like allocating memory to hold an image.  You will have to
 * supply these parts to get it to compile.  For an example of a minimal
 * working PNG reader/writer, see pngtest.c, included in this distribution.
 */

/* write a png file */

typedef struct SPPNGBD {
      const guchar *px;
      int rowstride;
} SPPNGBD;

static int
sp_png_get_block_stripe (const guchar **rows, int row, int num_rows, void *data)
{
      SPPNGBD *bd = (SPPNGBD *) data;

      for (int r = 0; r < num_rows; r++) {
            rows[r] = bd->px + (row + r) * bd->rowstride;
      }

      return num_rows;
}

int
sp_png_write_rgba (const gchar *filename, const guchar *px, int width, int height, int rowstride)
{
      SPPNGBD bd;

      bd.px = px;
      bd.rowstride = rowstride;

      return sp_png_write_rgba_striped (filename, width, height, sp_png_get_block_stripe, &bd);
}

int
sp_png_write_rgba_striped (const gchar *filename, int width, int height,
                     int (* get_rows) (const guchar **rows, int row, int num_rows, void *data),
                     void *data)
{
      FILE *fp;
      png_structp png_ptr;
      png_infop info_ptr;
      png_color_8 sig_bit;
      png_text text_ptr[3];
      png_uint_32 r;

      g_return_val_if_fail (filename != NULL, FALSE);

      /* open the file */

      Inkscape::IO::dump_fopen_call(filename, "M");
      fp = Inkscape::IO::fopen_utf8name(filename, "wb");
      g_return_val_if_fail (fp != NULL, FALSE);

      /* Create and initialize the png_struct with the desired error handler
       * functions.  If you want to use the default stderr and longjump method,
       * you can supply NULL for the last three parameters.  We also check that
       * the library version is compatible with the one used at compile time,
       * in case we are using dynamically linked libraries.  REQUIRED.
       */
      png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);

      if (png_ptr == NULL) {
            fclose(fp);
            return FALSE;
      }

      /* Allocate/initialize the image information data.  REQUIRED */
      info_ptr = png_create_info_struct(png_ptr);
      if (info_ptr == NULL) {
            fclose(fp);
            png_destroy_write_struct(&png_ptr, NULL);
            return FALSE;
      }

      /* Set error handling.  REQUIRED if you aren't supplying your own
       * error hadnling functions in the png_create_write_struct() call.
       */
      if (setjmp(png_ptr->jmpbuf)) {
            /* If we get here, we had a problem reading the file */
            fclose(fp);
            png_destroy_write_struct(&png_ptr, &info_ptr);
            return FALSE;
      }

      /* set up the output control if you are using standard C streams */
      png_init_io(png_ptr, fp);

      /* Set the image information here.  Width and height are up to 2^31,
       * bit_depth is one of 1, 2, 4, 8, or 16, but valid values also depend on
       * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,
       * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,
       * or PNG_COLOR_TYPE_RGB_ALPHA.  interlace is either PNG_INTERLACE_NONE or
       * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST
       * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE. REQUIRED
       */
      png_set_IHDR(png_ptr, info_ptr,
                 width,
                 height,
                 8, /* bit_depth */
                 PNG_COLOR_TYPE_RGB_ALPHA,
                 PNG_INTERLACE_NONE,
                 PNG_COMPRESSION_TYPE_BASE,
                 PNG_FILTER_TYPE_BASE);

      /* otherwise, if we are dealing with a color image then */
      sig_bit.red = 8;
      sig_bit.green = 8;
      sig_bit.blue = 8;
      /* if the image has an alpha channel then */
      sig_bit.alpha = 8;
      png_set_sBIT(png_ptr, info_ptr, &sig_bit);

      /* Made by Inkscape comment */
      text_ptr[0].key = "Software";
      text_ptr[0].text = "www.inkscape.org";
      text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE;
      png_set_text(png_ptr, info_ptr, text_ptr, 1);

      /* other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs, */
      /* note that if sRGB is present the cHRM chunk must be ignored
       * on read and must be written in accordance with the sRGB profile */

      /* Write the file header information.  REQUIRED */
      png_write_info(png_ptr, info_ptr);

      /* Once we write out the header, the compression type on the text
       * chunks gets changed to PNG_TEXT_COMPRESSION_NONE_WR or
       * PNG_TEXT_COMPRESSION_zTXt_WR, so it doesn't get written out again
       * at the end.
       */

      /* set up the transformations you want.  Note that these are
       * all optional.  Only call them if you want them.
       */

      /* --- CUT --- */

      /* The easiest way to write the image (you may have a different memory
       * layout, however, so choose what fits your needs best).  You need to
       * use the first method if you aren't handling interlacing yourself.
       */

      r = 0;
      while (r < static_cast< png_uint_32 > (height) ) {
            png_bytep row_pointers[64];
            int h, n;

            h = MIN (height - r, 64);
            n = get_rows ((const unsigned char **) row_pointers, r, h, data);
            if (!n) break;
            png_write_rows (png_ptr, row_pointers, n);
            r += n;
      }

      /* You can write optional chunks like tEXt, zTXt, and tIME at the end
       * as well.
       */

      /* It is REQUIRED to call this to finish writing the rest of the file */
      png_write_end(png_ptr, info_ptr);

      /* if you allocated any text comments, free them here */

      /* clean up after the write, and free any memory allocated */
      png_destroy_write_struct(&png_ptr, &info_ptr);

      /* close the file */
      fclose(fp);

      /* that's it */
      return TRUE;
}


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