00001 /* 00002 * jdatadst_stdio.c 00003 * 00004 * Copyright (C) 1994-1996, Thomas G. Lane. 00005 * Modified 2009 by Guido Vollbeding. 00006 * This file is part of the Independent JPEG Group's software. 00007 * For conditions of distribution and use, see the accompanying README file. 00008 * 00009 * This file contains compression data destination routines for the case of 00010 * emitting JPEG data to memory or to a file (or any stdio stream). 00011 * While these routines are sufficient for most applications, 00012 * some will want to use a different destination manager. 00013 * IMPORTANT: we assume that fwrite() will correctly transcribe an array of 00014 * JOCTETs into 8-bit-wide elements on external storage. If char is wider 00015 * than 8 bits on your machine, you may need to do some tweaking. 00016 */ 00017 00018 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */ 00019 #include "jinclude.h" 00020 #include "jpeglib.h" 00021 #include "jerror.h" 00022 00023 #ifndef HAVE_STDLIB_H /* <stdlib.h> should declare malloc(),free() */ 00024 extern void * malloc JPP((size_t size)); 00025 extern void free JPP((void *ptr)); 00026 #endif 00027 00028 /* Expanded data destination object for stdio output */ 00029 00030 typedef struct { 00031 struct jpeg_destination_mgr pub; /* public fields */ 00032 00033 FILE * outfile; /* target stream */ 00034 JOCTET * buffer; /* start of buffer */ 00035 } my_destination_mgr; 00036 00037 typedef my_destination_mgr * my_dest_ptr; 00038 00039 #define OUTPUT_BUF_SIZE 4096 /* choose an efficiently fwrite'able size */ 00040 00041 /* 00042 * Initialize destination --- called by jpeg_start_compress 00043 * before any data is actually written. 00044 */ 00045 00046 METHODDEF(void) 00047 init_destination (j_compress_ptr cinfo) 00048 { 00049 my_dest_ptr dest = (my_dest_ptr) cinfo->dest; 00050 00051 /* Allocate the output buffer --- it will be released when done with image */ 00052 dest->buffer = (JOCTET *) 00053 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 00054 OUTPUT_BUF_SIZE * SIZEOF(JOCTET)); 00055 00056 dest->pub.next_output_byte = dest->buffer; 00057 dest->pub.free_in_buffer = OUTPUT_BUF_SIZE; 00058 } 00059 00060 /* 00061 * Empty the output buffer --- called whenever buffer fills up. 00062 * 00063 * In typical applications, this should write the entire output buffer 00064 * (ignoring the current state of next_output_byte & free_in_buffer), 00065 * reset the pointer & count to the start of the buffer, and return TRUE 00066 * indicating that the buffer has been dumped. 00067 * 00068 * In applications that need to be able to suspend compression due to output 00069 * overrun, a FALSE return indicates that the buffer cannot be emptied now. 00070 * In this situation, the compressor will return to its caller (possibly with 00071 * an indication that it has not accepted all the supplied scanlines). The 00072 * application should resume compression after it has made more room in the 00073 * output buffer. Note that there are substantial restrictions on the use of 00074 * suspension --- see the documentation. 00075 * 00076 * When suspending, the compressor will back up to a convenient restart point 00077 * (typically the start of the current MCU). next_output_byte & free_in_buffer 00078 * indicate where the restart point will be if the current call returns FALSE. 00079 * Data beyond this point will be regenerated after resumption, so do not 00080 * write it out when emptying the buffer externally. 00081 */ 00082 00083 METHODDEF(boolean) 00084 empty_output_buffer (j_compress_ptr cinfo) 00085 { 00086 my_dest_ptr dest = (my_dest_ptr) cinfo->dest; 00087 00088 if (JFWRITE(dest->outfile, dest->buffer, OUTPUT_BUF_SIZE) != 00089 (size_t) OUTPUT_BUF_SIZE) 00090 ERREXIT(cinfo, JERR_FILE_WRITE); 00091 00092 dest->pub.next_output_byte = dest->buffer; 00093 dest->pub.free_in_buffer = OUTPUT_BUF_SIZE; 00094 00095 return TRUE; 00096 } 00097 00098 /* 00099 * Terminate destination --- called by jpeg_finish_compress 00100 * after all data has been written. Usually needs to flush buffer. 00101 * 00102 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding 00103 * application must deal with any cleanup that should happen even 00104 * for error exit. 00105 */ 00106 00107 METHODDEF(void) 00108 term_destination (j_compress_ptr cinfo) 00109 { 00110 my_dest_ptr dest = (my_dest_ptr) cinfo->dest; 00111 size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer; 00112 00113 /* Write any data remaining in the buffer */ 00114 if (datacount > 0) { 00115 if (JFWRITE(dest->outfile, dest->buffer, datacount) != datacount) 00116 ERREXIT(cinfo, JERR_FILE_WRITE); 00117 } 00118 fflush(dest->outfile); 00119 /* Make sure we wrote the output file OK */ 00120 if (ferror(dest->outfile)) 00121 ERREXIT(cinfo, JERR_FILE_WRITE); 00122 } 00123 00124 /* 00125 * Prepare for output to a stdio stream. 00126 * The caller must have already opened the stream, and is responsible 00127 * for closing it after finishing compression. 00128 */ 00129 00130 GLOBAL(void) 00131 jpeg_stdio_dest (j_compress_ptr cinfo, FILE * outfile) 00132 { 00133 my_dest_ptr dest; 00134 00135 /* The destination object is made permanent so that multiple JPEG images 00136 * can be written to the same file without re-executing jpeg_stdio_dest. 00137 * This makes it dangerous to use this manager and a different destination 00138 * manager serially with the same JPEG object, because their private object 00139 * sizes may be different. Caveat programmer. 00140 */ 00141 if (cinfo->dest == NULL) { /* first time for this JPEG object? */ 00142 cinfo->dest = (struct jpeg_destination_mgr *) 00143 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT, 00144 SIZEOF(my_destination_mgr)); 00145 } 00146 00147 dest = (my_dest_ptr) cinfo->dest; 00148 dest->pub.init_destination = init_destination; 00149 dest->pub.empty_output_buffer = empty_output_buffer; 00150 dest->pub.term_destination = term_destination; 00151 dest->outfile = outfile; 00152 }