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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 } |