jdatadst.cpp

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          http://www.mrpt.org/                          |
   |                                                                        |
   | Copyright (c) 2005-2017, Individual contributors, see AUTHORS file     |
   | See: http://www.mrpt.org/Authors - All rights reserved.                |
   | Released under BSD License. See details in http://www.mrpt.org/License |
   +------------------------------------------------------------------------+ */

/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
#include "jinclude.h"
#include "mrpt_jpeglib.h"
#include "jerror.h"

/* Expanded data destination object for stdio output */

typedef struct
{
        struct jpeg_destination_mgr pub; /* public fields */

        FILE* outfile; /* target stream */
        JOCTET* buffer; /* start of buffer */
} my_destination_mgr;

typedef my_destination_mgr* my_dest_ptr;

#define OUTPUT_BUF_SIZE 4096 /* choose an efficiently fwrite'able size */

/*
 * Initialize destination --- called by jpeg_start_compress
 * before any data is actually written.
 */

METHODDEF(void)
init_destination(j_compress_ptr cinfo)
{
        my_dest_ptr dest = (my_dest_ptr)cinfo->dest;

        /* Allocate the output buffer --- it will be released when done with image
         */
        dest->buffer = (JOCTET*)(*cinfo->mem->alloc_small)(
                (j_common_ptr)cinfo, JPOOL_IMAGE, OUTPUT_BUF_SIZE * SIZEOF(JOCTET));

        dest->pub.next_output_byte = dest->buffer;
        dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
}

/*
 * Empty the output buffer --- called whenever buffer fills up.
 *
 * In typical applications, this should write the entire output buffer
 * (ignoring the current state of next_output_byte & free_in_buffer),
 * reset the pointer & count to the start of the buffer, and return TRUE
 * indicating that the buffer has been dumped.
 *
 * In applications that need to be able to suspend compression due to output
 * overrun, a FALSE return indicates that the buffer cannot be emptied now.
 * In this situation, the compressor will return to its caller (possibly with
 * an indication that it has not accepted all the supplied scanlines).  The
 * application should resume compression after it has made more room in the
 * output buffer.  Note that there are substantial restrictions on the use of
 * suspension --- see the documentation.
 *
 * When suspending, the compressor will back up to a convenient restart point
 * (typically the start of the current MCU). next_output_byte & free_in_buffer
 * indicate where the restart point will be if the current call returns FALSE.
 * Data beyond this point will be regenerated after resumption, so do not
 * write it out when emptying the buffer externally.
 */

METHODDEF(boolean)
empty_output_buffer(j_compress_ptr cinfo)
{
        my_dest_ptr dest = (my_dest_ptr)cinfo->dest;

        if (JFWRITE(dest->outfile, dest->buffer, OUTPUT_BUF_SIZE) !=
                (size_t)OUTPUT_BUF_SIZE)
                ERREXIT(cinfo, JERR_FILE_WRITE);

        dest->pub.next_output_byte = dest->buffer;
        dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;

        return TRUE;
}

/*
 * Terminate destination --- called by jpeg_finish_compress
 * after all data has been written.  Usually needs to flush buffer.
 *
 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 * application must deal with any cleanup that should happen even
 * for error exit.
 */

METHODDEF(void)
term_destination(j_compress_ptr cinfo)
{
        my_dest_ptr dest = (my_dest_ptr)cinfo->dest;
        size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;

        /* Write any data remaining in the buffer */
        if (datacount > 0)
        {
                if (JFWRITE(dest->outfile, dest->buffer, datacount) != datacount)
                        ERREXIT(cinfo, JERR_FILE_WRITE);
        }
        fflush(dest->outfile);
        /* Make sure we wrote the output file OK */
        if (ferror(dest->outfile)) ERREXIT(cinfo, JERR_FILE_WRITE);
}

/*
 * Prepare for output to a stdio stream.
 * The caller must have already opened the stream, and is responsible
 * for closing it after finishing compression.
 */

GLOBAL(void)
jpeg_stdio_dest(j_compress_ptr cinfo, FILE* outfile)
{
        my_dest_ptr dest;

        /* The destination object is made permanent so that multiple JPEG images
         * can be written to the same file without re-executing jpeg_stdio_dest.
         * This makes it dangerous to use this manager and a different destination
         * manager serially with the same JPEG object, because their private object
         * sizes may be different.  Caveat programmer.
         */
        if (cinfo->dest == nullptr)
        { /* first time for this JPEG object? */
                cinfo->dest = (struct jpeg_destination_mgr*)(*cinfo->mem->alloc_small)(
                        (j_common_ptr)cinfo, JPOOL_PERMANENT, SIZEOF(my_destination_mgr));
        }

        dest = (my_dest_ptr)cinfo->dest;
        dest->pub.init_destination = init_destination;
        dest->pub.empty_output_buffer = empty_output_buffer;
        dest->pub.term_destination = term_destination;
        dest->outfile = outfile;
}