4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * This file is part of the Independent JPEG Group's software.
6 * For conditions of distribution and use, see the accompanying README file.
8 * This file contains compression data destination routines for the case of
9 * emitting JPEG data to a file (or any stdio stream). While these routines
10 * are sufficient for most applications, some will want to use a different
11 * destination manager.
12 * IMPORTANT: we assume that fwrite() will correctly transcribe an array of
13 * JOCTETs into 8-bit-wide elements on external storage. If char is wider
14 * than 8 bits on your machine, you may need to do some tweaking.
17 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
20 /* Expanded data destination object for stdio output */
23 typedef boolean(*boolean_jpeg_compress_struct)(jpeg_compress_struct*);
24 typedef void(*void_jpeg_compress_struct)(jpeg_compress_struct*);
28 struct jpeg_destination_mgr pub; /* public fields */
30 std::ostream * outfile; /* target stream */
31 JOCTET * buffer; /* start of buffer */
32 // boolean start_of_file; /* have we gotten any data yet? */
34 size_t frag_length; //we have to control this one to spec the size of the frag
38 typedef my_destination_mgr * my_dest_ptr;
40 #define OUTPUT_BUF_SIZE 4096 /* choose an efficiently fwrite'able size */
44 * Initialize destination --- called by jpeg_start_compress
45 * before any data is actually written.
49 init_destination (j_compress_ptr cinfo)
51 my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
53 /* Allocate the output buffer --- it will be released when done with image */
54 dest->buffer = (JOCTET *)
55 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
56 OUTPUT_BUF_SIZE * SIZEOF(JOCTET));
58 dest->pub.next_output_byte = dest->buffer;
59 dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
64 * Empty the output buffer --- called whenever buffer fills up.
66 * In typical applications, this should write the entire output buffer
67 * (ignoring the current state of next_output_byte & free_in_buffer),
68 * reset the pointer & count to the start of the buffer, and return TRUE
69 * indicating that the buffer has been dumped.
71 * In applications that need to be able to suspend compression due to output
72 * overrun, a FALSE return indicates that the buffer cannot be emptied now.
73 * In this situation, the compressor will return to its caller (possibly with
74 * an indication that it has not accepted all the supplied scanlines). The
75 * application should resume compression after it has made more room in the
76 * output buffer. Note that there are substantial restrictions on the use of
77 * suspension --- see the documentation.
79 * When suspending, the compressor will back up to a convenient restart point
80 * (typically the start of the current MCU). next_output_byte & free_in_buffer
81 * indicate where the restart point will be if the current call returns FALSE.
82 * Data beyond this point will be regenerated after resumption, so do not
83 * write it out when emptying the buffer externally.
87 empty_output_buffer (j_compress_ptr cinfo)
89 my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
91 if( dest->bytes_written == dest->frag_length )
93 // Start the I/O suspension simply by returning false here:
97 size_t output_buf_size = OUTPUT_BUF_SIZE;
98 if( (dest->bytes_written + OUTPUT_BUF_SIZE) > dest->frag_length )
100 output_buf_size = dest->frag_length - dest->bytes_written;
102 dest->outfile->write((char*)dest->buffer, output_buf_size);
103 size_t nbytes = output_buf_size; //dest->outfile->gcount();
106 ERREXIT(cinfo, JERR_FILE_WRITE);
108 if( dest->outfile->fail() )
109 ERREXIT(cinfo, JERR_FILE_WRITE);
111 dest->pub.next_output_byte = dest->buffer;
112 dest->pub.free_in_buffer = nbytes; //OUTPUT_BUF_SIZE;
113 dest->bytes_written += nbytes;
120 * Terminate destination --- called by jpeg_finish_compress
121 * after all data has been written. Usually needs to flush buffer.
123 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
124 * application must deal with any cleanup that should happen even
129 term_destination (j_compress_ptr cinfo)
131 my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
132 size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;
134 /* Write any data remaining in the buffer */
137 if (JFWRITE(dest->outfile, dest->buffer, datacount) != datacount)
138 ERREXIT(cinfo, JERR_FILE_WRITE);
140 fflush(dest->outfile);
141 /* Make sure we wrote the output file OK */
142 if (ferror(dest->outfile))
143 ERREXIT(cinfo, JERR_FILE_WRITE);
146 dest->outfile->write((char*)dest->buffer, datacount);
147 if (dest->outfile->fail())
148 ERREXIT(cinfo, JERR_FILE_WRITE);
149 dest->outfile->flush();
150 /* Make sure we wrote the output file OK */
151 if (dest->outfile->fail())
152 ERREXIT(cinfo, JERR_FILE_WRITE);
159 * Prepare for output to a stdio stream.
160 * The caller must have already opened the stream, and is responsible
161 * for closing it after finishing compression.
165 jpeg_stdio_dest (j_compress_ptr cinfo, std::ostream * outfile, size_t frag_length, int flag)
169 /* The destination object is made permanent so that multiple JPEG images
170 * can be written to the same file without re-executing jpeg_stdio_dest.
171 * This makes it dangerous to use this manager and a different destination
172 * manager serially with the same JPEG object, because their private object
173 * sizes may be different. Caveat programmer.
175 if (cinfo->dest == NULL) { /* first time for this JPEG object? */
176 cinfo->dest = (struct jpeg_destination_mgr *)
177 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
178 SIZEOF(my_destination_mgr));
181 dest = (my_dest_ptr) cinfo->dest;
182 dest->pub.init_destination = reinterpret_cast<void_jpeg_compress_struct>(init_destination);
183 dest->pub.empty_output_buffer = reinterpret_cast<boolean_jpeg_compress_struct>(empty_output_buffer);
184 dest->pub.term_destination = reinterpret_cast<void_jpeg_compress_struct>(term_destination);
185 dest->outfile = outfile;
187 // Need to setup a new buffer, clean bytes_in_buffer and next_input_byte
190 dest->bytes_written = 0;
192 // only upate the new fragment, valid for both 'flag' value
193 dest->frag_length = frag_length;