128 lines
6.3 KiB
C++
128 lines
6.3 KiB
C++
//$T JDATADST.C GC! 1.081 01/25/01 08:49:34
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// * jdatadst.c Copyright (C) 1994, Thomas G. Lane. This file is part of the
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// * Independent JPEG Group's software. For conditions of distribution and use, see
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// * the accompanying README file. This file contains compression data destination
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// * routines for the case of emitting JPEG data to a file (or any stdio stream).
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// * While these routines are sufficient for most applications, some will want to
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// * use a different destination manager. IMPORTANT: we assume that fwrite() will
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// * correctly transcribe an array of JOCTETs into 8-bit-wide elements on external
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// * storage. If char is wider than 8 bits on your machine, you may need to do some
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// * tweaking.
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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 "INTERFCE.h"
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#include "JPEGLIB.h"
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#include "JERROR.h"
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// -----------------------------------------------------------------------------------------------------------------------
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// Expanded data destination object for stdio output
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// -----------------------------------------------------------------------------------------------------------------------
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typedef struct
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{
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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 before any data is actually written.
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// =======================================================================================================================
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METHODDEF void init_destination(j_compress_ptr cinfo)
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{
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my_dest_ptr dest;
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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 *) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 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. In typical applications, this should write the entire
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// output buffer (ignoring the current state of next_output_byte & free_in_buffer), reset the pointer & count to the
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// start of the buffer, and return TRUE indicating that the buffer has been dumped. In applications that need to be
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// able to suspend compression due to output 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 an indication that it has not accepted
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// all the supplied scanlines). The application should resume compression after it has made more room in the output
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// buffer. Note that there are substantial restrictions on the use of suspension --- see the documentation. When
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// suspending, the compressor will back up to a convenient restart point (typically the start of the current MCU).
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// next_output_byte & free_in_buffer indicate where the restart point will be if the current call returns FALSE. Data
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// beyond this point will be regenerated after resumption, so do not write it out when emptying the buffer externally.
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// =======================================================================================================================
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METHODDEF boolean empty_output_buffer(j_compress_ptr cinfo)
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{
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my_dest_ptr pst_Dest;
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char *pc_Buffer;
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pst_Dest = (my_dest_ptr) cinfo->dest;
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pc_Buffer = ((char *) pst_Dest->outfile) + lJPEG_INPOUT_FILE_LENGHT;
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JFWRITE(pc_Buffer, pst_Dest->buffer, OUTPUT_BUF_SIZE);
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lJPEG_INPOUT_FILE_LENGHT += OUTPUT_BUF_SIZE;
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pst_Dest->pub.next_output_byte = pst_Dest->buffer;
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pst_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 after all data has been written. Usually needs to flush
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// buffer. NB: *not* called by jpeg_abort or jpeg_destroy; surrounding application must deal with any cleanup that
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// should happen even for error exit.
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// =======================================================================================================================
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METHODDEF void term_destination(j_compress_ptr cinfo)
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{
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my_dest_ptr pst_Dest;
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char *pc_Buffer;
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size_t datacount;
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pst_Dest = (my_dest_ptr) cinfo->dest;
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datacount = OUTPUT_BUF_SIZE - pst_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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{
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pc_Buffer = ((char *) pst_Dest->outfile) + lJPEG_INPOUT_FILE_LENGHT;
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JFWRITE(pc_Buffer, pst_Dest->buffer, OUTPUT_BUF_SIZE);
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lJPEG_INPOUT_FILE_LENGHT += datacount;
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}
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}
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// =======================================================================================================================
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// Prepare for output to a stdio stream. The caller must have already opened the stream, and is responsible for
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// closing it after finishing compression.
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// =======================================================================================================================
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GLOBAL void 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 can be
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// * written to the same file without re-executing jpeg_stdio_dest. This makes it
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// * dangerous to use this manager and a different destination manager serially with
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// * the same JPEG object, because their private object sizes may be different.
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// * Caveat programmer.
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if(cinfo->dest == NULL) // first time for this JPEG object?
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{
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cinfo->dest = (struct jpeg_destination_mgr *) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT, 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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