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1 /*
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2 * jdatadst.c
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3 *
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4 * Copyright (C) 1994-1996, Thomas G. Lane.
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5 * This file is part of the Independent JPEG Group's software.
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6 * For conditions of distribution and use, see the accompanying README file.
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7 *
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8 * This file contains compression data destination routines for the case of
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9 * emitting JPEG data to a file (or any stdio stream). While these routines
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10 * are sufficient for most applications, some will want to use a different
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11 * destination manager.
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12 * IMPORTANT: we assume that fwrite() will correctly transcribe an array of
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13 * JOCTETs into 8-bit-wide elements on external storage. If char is wider
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14 * than 8 bits on your machine, you may need to do some tweaking.
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15 */
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16
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17 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
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18 #include "jinclude.h"
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19 #include "jpeglib.h"
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20 #include "jerror.h"
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21
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22
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23 /* Expanded data destination object for stdio output */
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24
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25 typedef struct {
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26 struct jpeg_destination_mgr pub; /* public fields */
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27
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28 FILE * outfile; /* target stream */
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29 JOCTET * buffer; /* start of buffer */
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30 } my_destination_mgr;
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31
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32 typedef my_destination_mgr * my_dest_ptr;
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33
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34 #define OUTPUT_BUF_SIZE 4096 /* choose an efficiently fwrite'able size */
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35
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36
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37 /*
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38 * Initialize destination --- called by jpeg_start_compress
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39 * before any data is actually written.
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40 */
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41
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42 METHODDEF(void)
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43 init_destination (j_compress_ptr cinfo)
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44 {
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45 my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
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46
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47 /* Allocate the output buffer --- it will be released when done with image */
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48 dest->buffer = (JOCTET *)
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49 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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50 OUTPUT_BUF_SIZE * SIZEOF(JOCTET));
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51
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52 dest->pub.next_output_byte = dest->buffer;
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53 dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
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54 }
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55
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56
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57 /*
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58 * Empty the output buffer --- called whenever buffer fills up.
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59 *
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60 * In typical applications, this should write the entire output buffer
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61 * (ignoring the current state of next_output_byte & free_in_buffer),
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62 * reset the pointer & count to the start of the buffer, and return TRUE
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63 * indicating that the buffer has been dumped.
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64 *
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65 * In applications that need to be able to suspend compression due to output
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66 * overrun, a FALSE return indicates that the buffer cannot be emptied now.
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67 * In this situation, the compressor will return to its caller (possibly with
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68 * an indication that it has not accepted all the supplied scanlines). The
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69 * application should resume compression after it has made more room in the
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70 * output buffer. Note that there are substantial restrictions on the use of
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71 * suspension --- see the documentation.
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72 *
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73 * When suspending, the compressor will back up to a convenient restart point
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74 * (typically the start of the current MCU). next_output_byte & free_in_buffer
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75 * indicate where the restart point will be if the current call returns FALSE.
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76 * Data beyond this point will be regenerated after resumption, so do not
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77 * write it out when emptying the buffer externally.
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78 */
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79
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80 METHODDEF(boolean)
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81 empty_output_buffer (j_compress_ptr cinfo)
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82 {
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83 my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
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84
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85 if (JFWRITE(dest->outfile, dest->buffer, OUTPUT_BUF_SIZE) !=
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86 (size_t) OUTPUT_BUF_SIZE)
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87 ERREXIT(cinfo, JERR_FILE_WRITE);
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88
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89 dest->pub.next_output_byte = dest->buffer;
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90 dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
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91
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92 return TRUE;
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93 }
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94
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95
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96 /*
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97 * Terminate destination --- called by jpeg_finish_compress
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98 * after all data has been written. Usually needs to flush buffer.
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99 *
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100 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
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101 * application must deal with any cleanup that should happen even
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102 * for error exit.
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103 */
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104
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105 METHODDEF(void)
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106 term_destination (j_compress_ptr cinfo)
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107 {
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108 my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
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109 size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;
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110
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111 /* Write any data remaining in the buffer */
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112 if (datacount > 0) {
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113 if (JFWRITE(dest->outfile, dest->buffer, datacount) != datacount)
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114 ERREXIT(cinfo, JERR_FILE_WRITE);
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115 }
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116 fflush(dest->outfile);
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117 /* Make sure we wrote the output file OK */
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118 if (ferror(dest->outfile))
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119 ERREXIT(cinfo, JERR_FILE_WRITE);
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120 }
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121
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122
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123 /*
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124 * Prepare for output to a stdio stream.
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125 * The caller must have already opened the stream, and is responsible
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126 * for closing it after finishing compression.
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127 */
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128
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129 GLOBAL(void)
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130 jpeg_stdio_dest (j_compress_ptr cinfo, FILE * outfile)
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131 {
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132 my_dest_ptr dest;
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133
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134 /* The destination object is made permanent so that multiple JPEG images
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135 * can be written to the same file without re-executing jpeg_stdio_dest.
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136 * This makes it dangerous to use this manager and a different destination
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137 * manager serially with the same JPEG object, because their private object
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138 * sizes may be different. Caveat programmer.
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139 */
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140 if (cinfo->dest == NULL) { /* first time for this JPEG object? */
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141 cinfo->dest = (struct jpeg_destination_mgr *)
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142 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
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143 SIZEOF(my_destination_mgr));
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144 }
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145
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146 dest = (my_dest_ptr) cinfo->dest;
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147 dest->pub.init_destination = init_destination;
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148 dest->pub.empty_output_buffer = empty_output_buffer;
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149 dest->pub.term_destination = term_destination;
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150 dest->outfile = outfile;
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151 }
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