152 lines
5.1 KiB
C
152 lines
5.1 KiB
C
/*
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* jdatadst.c
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*
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* Copyright (C) 1994-1996, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This file contains compression data destination routines for the case of
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* emitting JPEG data to a file (or any stdio stream). While these routines
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* are sufficient for most applications, some will want to use a different
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* destination manager.
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* IMPORTANT: we assume that fwrite() will correctly transcribe an array of
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* JOCTETs into 8-bit-wide elements on external storage. If char is wider
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* than 8 bits on your machine, you may need to do some tweaking.
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*/
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/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
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#include "jinclude.h"
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#include "jpeglib.h"
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#include "jerror.h"
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/* Expanded data destination object for stdio output */
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typedef struct {
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struct jpeg_destination_mgr pub; /* public fields */
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FILE * outfile; /* target stream */
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JOCTET * buffer; /* start of buffer */
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} my_destination_mgr;
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typedef my_destination_mgr * my_dest_ptr;
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#define OUTPUT_BUF_SIZE 4096 /* choose an efficiently fwrite'able size */
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/*
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* Initialize destination --- called by jpeg_start_compress
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* before any data is actually written.
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*/
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METHODDEF(void)
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init_destination (j_compress_ptr cinfo)
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{
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my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
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/* Allocate the output buffer --- it will be released when done with image */
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dest->buffer = (JOCTET *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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OUTPUT_BUF_SIZE * SIZEOF(JOCTET));
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dest->pub.next_output_byte = dest->buffer;
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dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
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}
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/*
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* Empty the output buffer --- called whenever buffer fills up.
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*
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* In typical applications, this should write the entire output buffer
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* (ignoring the current state of next_output_byte & free_in_buffer),
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* reset the pointer & count to the start of the buffer, and return TRUE
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* indicating that the buffer has been dumped.
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*
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* In applications that need to be able to suspend compression due to output
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* overrun, a FALSE return indicates that the buffer cannot be emptied now.
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* In this situation, the compressor will return to its caller (possibly with
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* an indication that it has not accepted all the supplied scanlines). The
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* application should resume compression after it has made more room in the
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* output buffer. Note that there are substantial restrictions on the use of
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* suspension --- see the documentation.
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*
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* When suspending, the compressor will back up to a convenient restart point
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* (typically the start of the current MCU). next_output_byte & free_in_buffer
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* indicate where the restart point will be if the current call returns FALSE.
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* Data beyond this point will be regenerated after resumption, so do not
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* write it out when emptying the buffer externally.
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*/
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METHODDEF(boolean)
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empty_output_buffer (j_compress_ptr cinfo)
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{
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my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
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if (JFWRITE(dest->outfile, dest->buffer, OUTPUT_BUF_SIZE) !=
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(size_t) OUTPUT_BUF_SIZE)
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ERREXIT(cinfo, JERR_FILE_WRITE);
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dest->pub.next_output_byte = dest->buffer;
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dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
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return TRUE;
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}
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/*
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* Terminate destination --- called by jpeg_finish_compress
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* after all data has been written. Usually needs to flush buffer.
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*
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* NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
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* application must deal with any cleanup that should happen even
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* for error exit.
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*/
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METHODDEF(void)
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term_destination (j_compress_ptr cinfo)
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{
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my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
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size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;
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/* Write any data remaining in the buffer */
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if (datacount > 0) {
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if (JFWRITE(dest->outfile, dest->buffer, datacount) != datacount)
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ERREXIT(cinfo, JERR_FILE_WRITE);
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}
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fflush(dest->outfile);
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/* Make sure we wrote the output file OK */
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if (ferror(dest->outfile))
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ERREXIT(cinfo, JERR_FILE_WRITE);
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}
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/*
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* Prepare for output to a stdio stream.
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* The caller must have already opened the stream, and is responsible
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* for closing it after finishing compression.
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*/
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GLOBAL(void)
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jpeg_stdio_dest (j_compress_ptr cinfo, FILE * outfile)
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{
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my_dest_ptr dest;
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/* The destination object is made permanent so that multiple JPEG images
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* can be written to the same file without re-executing jpeg_stdio_dest.
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* This makes it dangerous to use this manager and a different destination
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* manager serially with the same JPEG object, because their private object
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* sizes may be different. Caveat programmer.
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*/
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if (cinfo->dest == NULL) { /* first time for this JPEG object? */
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cinfo->dest = (struct jpeg_destination_mgr *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
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SIZEOF(my_destination_mgr));
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}
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dest = (my_dest_ptr) cinfo->dest;
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dest->pub.init_destination = init_destination;
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dest->pub.empty_output_buffer = empty_output_buffer;
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dest->pub.term_destination = term_destination;
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dest->outfile = outfile;
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}
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