ref: b1d957de163081057eac05c26d502f6c28fc6dc8
dir: /common/id3lib/src/frame_render.cpp/
// $Id: frame_render.cpp,v 1.1 2002/01/21 08:16:22 menno Exp $
// id3lib: a C++ library for creating and manipulating id3v1/v2 tags
// Copyright 1999, 2000 Scott Thomas Haug
// This library is free software; you can redistribute it and/or modify it
// under the terms of the GNU Library General Public License as published by
// the Free Software Foundation; either version 2 of the License, or (at your
// option) any later version.
//
// This library is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
// License for more details.
//
// You should have received a copy of the GNU Library General Public License
// along with this library; if not, write to the Free Software Foundation,
// Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
// The id3lib authors encourage improvements and optimisations to be sent to
// the id3lib coordinator. Please see the README file for details on where to
// send such submissions. See the AUTHORS file for a list of people who have
// contributed to id3lib. See the ChangeLog file for a list of changes to
// id3lib. These files are distributed with id3lib at
// http://download.sourceforge.net/id3lib/
#include <string.h>
#include <memory.h>
#include <zlib.h>
#include "tag.h"
#include "utils.h"
#if defined HAVE_CONFIG_H
#include <config.h>
#endif
// Ideally, Render should render the frame in the order it is parsed, starting
// with the header, then any extra info (resulting from header flags), and then
// the frame data, one field at a time. This, unfortunately, isn't possible.
// In order to render the frame header, the data size must be known. One could
// query the fields' sizes before rendering them, but it would be faster to
// render the fields and add their sizes (which is calculated and returned in
// the fields' Render function) at the same time.
//
// Even if we determined this extra processing to be acceptable, it isn't
// possible to precompute the frame data size without rendering them all when
// compression is enabled. When compression is enabled, then the header
// contains the size of the compressed data. So all the fields need to
// rendered to a buffer and compressed before the data size can even be
// calculated in this scenario. And the compressed data might even be
// discarded if it is no smaller than the uncompressed data.
//
// So, Render should progress more-or-less as follows. The fields should be
// rendered to the target buffer at its desired position (after the projected
// header and extra bytes (at most 2)). If compression has been specified,
// then compress it into a temporary buffer. If the compressed size is smaller
// than the uncompressed data, copy the temp buffer to the correct place in the
// target buffer. Finally, render the header and the extra info. The
// encryption and grouping id's shouldn't be rendered until after the
// compression takes place, since they will be rendered to a different spots in
// the buffer depending on whether or not the data is compressed. This is
// because the uncompressed data size must come after before the id's if the
// the data is compressed, but won't be rendered if the data isn't compressed.
//
// One could probably implement Render more "naturally" by using more
// dynamically allocated buffers, but that would degrade performance. Whether
// or not this performance degradation would cause a significant impact on the
// overall performane of typeical apps should be looked in to.
//
// So, in short, Render is a more complicated function than it should be, but
// it doesn't look like there's a much better way that's any faster.
size_t ID3_Frame::Render(uchar *buffer) const
{
if (NULL == buffer)
{
ID3_THROW(ID3E_NoBuffer);
}
uchar e_id = this->_GetEncryptionID(), g_id = this->_GetGroupingID();
size_t decompressed_size = 0;
size_t extras = ( e_id > 0 ? 1 : 0 ) + ( g_id > 0 ? 1 : 0 );
ID3_FrameHeader hdr = __hdr;
const size_t hdr_size = hdr.Size();
// 1. Write out the field data to the buffer, with the assumption that
// we won't be decompressing, since this is the usual behavior
ID3_TextEnc enc = ID3TE_ASCII;
size_t data_size = 0;
for (ID3_Field** fi = __fields; fi != __fields + __num_fields; fi++)
{
if ((*fi)->GetID() == ID3FN_TEXTENC)
{
enc = static_cast<ID3_TextEnc>((*fi)->Get());
}
if (*fi && (*fi)->InScope(ID3V2_LATEST))
{
(*fi)->SetEncoding(enc);
data_size += (*fi)->Render(&buffer[data_size + hdr_size + extras]);
}
}
// 2. Attempt to compress if specified
if (this->GetCompression())
{
// The zlib documentation specifies that the destination size needs to be
// an unsigned long at least 0.1% larger than the source buffer, plus 12
// bytes
unsigned long new_data_size = data_size + (data_size / 10) + 12;
uchar* compressed_data = new uchar[new_data_size];
if (NULL == compressed_data)
{
ID3_THROW(ID3E_NoMemory);
}
if (compress(compressed_data, &new_data_size, &buffer[hdr_size + extras],
data_size) != Z_OK)
{
ID3_THROW(ID3E_zlibError);
}
// if the compression actually saves space...
if ((new_data_size + sizeof(uint32)) < data_size)
{
// add 4 bytes to 'extras' for the decompressed size
extras += sizeof(uint32);
memcpy(&buffer[hdr_size + extras], compressed_data, new_data_size);
decompressed_size = data_size;
data_size = new_data_size;
}
delete [] compressed_data;
}
// determine which flags need to be set
hdr.SetDataSize(data_size + extras);
hdr.SetEncryption(e_id > 0);
hdr.SetGrouping(g_id > 0);
hdr.SetCompression(decompressed_size > 0);
hdr.Render(buffer);
uchar* data = buffer + hdr_size;
if (decompressed_size)
{
data += RenderNumber(data, decompressed_size);
}
if (e_id)
{
*data++ = e_id;
}
if (g_id)
{
*data++ = g_id;
}
__changed = false;
return hdr_size + extras + data_size;
}