compiler/libjpeg/test/example.c

   1 /*
   2     $Id$
   3 */
   4
   5 /*
   6  * example.c
   7  *
   8  * This file illustrates how to use the IJG code as a subroutine library
   9  * to read or write JPEG image files.  You should look at this code in
  10  * conjunction with the documentation file libjpeg.doc.
  11  *
  12  * This code will not do anything useful as-is, but it may be helpful as a
  13  * skeleton for constructing routines that call the JPEG library.
  14  *
  15  * We present these routines in the same coding style used in the JPEG code
  16  * (ANSI function definitions, etc); but you are of course free to code your
  17  * routines in a different style if you prefer.
  18  */
  19
  20 #include <stdio.h>
  21
  22 /*
  23  * Include file for users of JPEG library.
  24  * You will need to have included system headers that define at least
  25  * the typedefs FILE and size_t before you can include jpeglib.h.
  26  * (stdio.h is sufficient on ANSI-conforming systems.)
  27  * You may also wish to include "jerror.h".
  28  */
  29
  30 #include "jpeglib.h"
  31
  32 /*
  33  * <setjmp.h> is used for the optional error recovery mechanism shown in
  34  * the second part of the example.
  35  */
  36
  37 #include <setjmp.h>
  38
  39
  40
  41 /******************** JPEG COMPRESSION SAMPLE INTERFACE *******************/
  42
  43 /* This half of the example shows how to feed data into the JPEG compressor.
  44  * We present a minimal version that does not worry about refinements such
  45  * as error recovery (the JPEG code will just exit() if it gets an error).
  46  */
  47
  48
  49 /*
  50  * IMAGE DATA FORMATS:
  51  *
  52  * The standard input image format is a rectangular array of pixels, with
  53  * each pixel having the same number of "component" values (color channels).
  54  * Each pixel row is an array of JSAMPLEs (which typically are unsigned chars).
  55  * If you are working with color data, then the color values for each pixel
  56  * must be adjacent in the row; for example, R,G,B,R,G,B,R,G,B,... for 24-bit
  57  * RGB color.
  58  *
  59  * For this example, we'll assume that this data structure matches the way
  60  * our application has stored the image in memory, so we can just pass a
  61  * pointer to our image buffer.  In particular, let's say that the image is
  62  * RGB color and is described by:
  63  */
  64
  65 extern JSAMPLE * image_buffer;  /* Points to large array of R,G,B-order data */
  66 extern int image_height;        /* Number of rows in image */
  67 extern int image_width;         /* Number of columns in image */
  68
  69
  70 /*
  71  * Sample routine for JPEG compression.  We assume that the target file name
  72  * and a compression quality factor are passed in.
  73  */
  74
  75 JGLOBAL(void)
  76 write_JPEG_file (char * filename, int quality)
  77 {
  78   /* This struct contains the JPEG compression parameters and pointers to
  79    * working space (which is allocated as needed by the JPEG library).
  80    * It is possible to have several such structures, representing multiple
  81    * compression/decompression processes, in existence at once.  We refer
  82    * to any one struct (and its associated working data) as a "JPEG object".
  83    */
  84   struct jpeg_compress_struct cinfo;
  85   /* This struct represents a JPEG error handler.  It is declared separately
  86    * because applications often want to supply a specialized error handler
  87    * (see the second half of this file for an example).  But here we just
  88    * take the easy way out and use the standard error handler, which will
  89    * print a message on stderr and call exit() if compression fails.
  90    * Note that this struct must live as long as the main JPEG parameter
  91    * struct, to avoid dangling-pointer problems.
  92    */
  93   struct jpeg_error_mgr jerr;
  94   /* More stuff */
  95   FILE * outfile;               /* target file */
  96   JSAMPROW row_pointer[1];      /* pointer to JSAMPLE row[s] */
  97   int row_stride;               /* physical row width in image buffer */
  98
  99   /* Step 1: allocate and initialize JPEG compression object */
 100
 101   /* We have to set up the error handler first, in case the initialization
 102    * step fails.  (Unlikely, but it could happen if you are out of memory.)
 103    * This routine fills in the contents of struct jerr, and returns jerr's
 104    * address which we place into the link field in cinfo.
 105    */
 106   cinfo.err = jpeg_std_error(&jerr);
 107   /* Now we can initialize the JPEG compression object. */
 108   jpeg_create_compress(&cinfo);
 109
 110   /* Step 2: specify data destination (eg, a file) */
 111   /* Note: steps 2 and 3 can be done in either order. */
 112
 113   /* Here we use the library-supplied code to send compressed data to a
 114    * stdio stream.  You can also write your own code to do something else.
 115    * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
 116    * requires it in order to write binary files.
 117    */
 118   if ((outfile = fopen(filename, "wb")) == NULL) {
 119     fprintf(stderr, "can't open %s\n", filename);
 120     exit(1);
 121   }
 122   jpeg_stdio_dest(&cinfo, outfile);
 123
 124   /* Step 3: set parameters for compression */
 125
 126   /* First we supply a description of the input image.
 127    * Four fields of the cinfo struct must be filled in:
 128    */
 129   cinfo.image_width = image_width;      /* image width and height, in pixels */
 130   cinfo.image_height = image_height;
 131   cinfo.input_components = 3;           /* # of color components per pixel */
 132   cinfo.in_color_space = JCS_RGB;       /* colorspace of input image */
 133   /* Now use the library's routine to set default compression parameters.
 134    * (You must set at least cinfo.in_color_space before calling this,
 135    * since the defaults depend on the source color space.)
 136    */
 137   jpeg_set_defaults(&cinfo);
 138   /* Now you can set any non-default parameters you wish to.
 139    * Here we just illustrate the use of quality (quantization table) scaling:
 140    */
 141   jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */);
 142
 143   /* Step 4: Start compressor */
 144
 145   /* TRUE ensures that we will write a complete interchange-JPEG file.
 146    * Pass TRUE unless you are very sure of what you're doing.
 147    */
 148   jpeg_start_compress(&cinfo, TRUE);
 149
 150   /* Step 5: while (scan lines remain to be written) */
 151   /*           jpeg_write_scanlines(...); */
 152
 153   /* Here we use the library's state variable cinfo.next_scanline as the
 154    * loop counter, so that we don't have to keep track ourselves.
 155    * To keep things simple, we pass one scanline per call; you can pass
 156    * more if you wish, though.
 157    */
 158   row_stride = image_width * 3; /* JSAMPLEs per row in image_buffer */
 159
 160   while (cinfo.next_scanline < cinfo.image_height) {
 161     /* jpeg_write_scanlines expects an array of pointers to scanlines.
 162      * Here the array is only one element long, but you could pass
 163      * more than one scanline at a time if that's more convenient.
 164      */
 165     row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride];
 166     (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
 167   }
 168
 169   /* Step 6: Finish compression */
 170
 171   jpeg_finish_compress(&cinfo);
 172   /* After finish_compress, we can close the output file. */
 173   fclose(outfile);
 174
 175   /* Step 7: release JPEG compression object */
 176
 177   /* This is an important step since it will release a good deal of memory. */
 178   jpeg_destroy_compress(&cinfo);
 179
 180   /* And we're done! */
 181 }
 182
 183
 184 /*
 185  * SOME FINE POINTS:
 186  *
 187  * In the above loop, we ignored the return value of jpeg_write_scanlines,
 188  * which is the number of scanlines actually written.  We could get away
 189  * with this because we were only relying on the value of cinfo.next_scanline,
 190  * which will be incremented correctly.  If you maintain additional loop
 191  * variables then you should be careful to increment them properly.
 192  * Actually, for output to a stdio stream you needn't worry, because
 193  * then jpeg_write_scanlines will write all the lines passed (or else exit
 194  * with a fatal error).  Partial writes can only occur if you use a data
 195  * destination module that can demand suspension of the compressor.
 196  * (If you don't know what that's for, you don't need it.)
 197  *
 198  * If the compressor requires full-image buffers (for entropy-coding
 199  * optimization or a multi-scan JPEG file), it will create temporary
 200  * files for anything that doesn't fit within the maximum-memory setting.
 201  * (Note that temp files are NOT needed if you use the default parameters.)
 202  * On some systems you may need to set up a signal handler to ensure that
 203  * temporary files are deleted if the program is interrupted.  See libjpeg.doc.
 204  *
 205  * Scanlines MUST be supplied in top-to-bottom order if you want your JPEG
 206  * files to be compatible with everyone else's.  If you cannot readily read
 207  * your data in that order, you'll need an intermediate array to hold the
 208  * image.  See rdtarga.c or rdbmp.c for examples of handling bottom-to-top
 209  * source data using the JPEG code's internal virtual-array mechanisms.
 210  */
 211
 212
 213
 214 /******************** JPEG DECOMPRESSION SAMPLE INTERFACE *******************/
 215
 216 /* This half of the example shows how to read data from the JPEG decompressor.
 217  * It's a bit more refined than the above, in that we show:
 218  *   (a) how to modify the JPEG library's standard error-reporting behavior;
 219  *   (b) how to allocate workspace using the library's memory manager.
 220  *
 221  * Just to make this example a little different from the first one, we'll
 222  * assume that we do not intend to put the whole image into an in-memory
 223  * buffer, but to send it line-by-line someplace else.  We need a one-
 224  * scanline-high JSAMPLE array as a work buffer, and we will let the JPEG
 225  * memory manager allocate it for us.  This approach is actually quite useful
 226  * because we don't need to remember to deallocate the buffer separately: it
 227  * will go away automatically when the JPEG object is cleaned up.
 228  */
 229
 230
 231 /*
 232  * ERROR HANDLING:
 233  *
 234  * The JPEG library's standard error handler (jerror.c) is divided into
 235  * several "methods" which you can override individually.  This lets you
 236  * adjust the behavior without duplicating a lot of code, which you might
 237  * have to update with each future release.
 238  *
 239  * Our example here shows how to override the "error_exit" method so that
 240  * control is returned to the library's caller when a fatal error occurs,
 241  * rather than calling exit() as the standard error_exit method does.
 242  *
 243  * We use C's setjmp/longjmp facility to return control.  This means that the
 244  * routine which calls the JPEG library must first execute a setjmp() call to
 245  * establish the return point.  We want the replacement error_exit to do a
 246  * longjmp().  But we need to make the setjmp buffer accessible to the
 247  * error_exit routine.  To do this, we make a private extension of the
 248  * standard JPEG error handler object.  (If we were using C++, we'd say we
 249  * were making a subclass of the regular error handler.)
 250  *
 251  * Here's the extended error handler struct:
 252  */
 253
 254 struct my_error_mgr {
 255   struct jpeg_error_mgr pub;    /* "public" fields */
 256
 257   jmp_buf setjmp_buffer;        /* for return to caller */
 258 };
 259
 260 typedef struct my_error_mgr * my_error_ptr;
 261
 262 /*
 263  * Here's the routine that will replace the standard error_exit method:
 264  */
 265
 266 METHODDEF(void)
 267 my_error_exit (j_common_ptr cinfo)
 268 {
 269   /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */
 270   my_error_ptr myerr = (my_error_ptr) cinfo->err;
 271
 272   /* Always display the message. */
 273   /* We could postpone this until after returning, if we chose. */
 274   (*cinfo->err->output_message) (cinfo);
 275
 276   /* Return control to the setjmp point */
 277   longjmp(myerr->setjmp_buffer, 1);
 278 }
 279
 280
 281 /*
 282  * Sample routine for JPEG decompression.  We assume that the source file name
 283  * is passed in.  We want to return 1 on success, 0 on error.
 284  */
 285
 286
 287 JGLOBAL(int)
 288 read_JPEG_file (char * filename)
 289 {
 290   /* This struct contains the JPEG decompression parameters and pointers to
 291    * working space (which is allocated as needed by the JPEG library).
 292    */
 293   struct jpeg_decompress_struct cinfo;
 294   /* We use our private extension JPEG error handler.
 295    * Note that this struct must live as long as the main JPEG parameter
 296    * struct, to avoid dangling-pointer problems.
 297    */
 298   struct my_error_mgr jerr;
 299   /* More stuff */
 300   FILE * infile;                /* source file */
 301   JSAMPARRAY buffer;            /* Output row buffer */
 302   int row_stride;               /* physical row width in output buffer */
 303
 304   /* In this example we want to open the input file before doing anything else,
 305    * so that the setjmp() error recovery below can assume the file is open.
 306    * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
 307    * requires it in order to read binary files.
 308    */
 309
 310   if ((infile = fopen(filename, "rb")) == NULL) {
 311     fprintf(stderr, "can't open %s\n", filename);
 312     return 0;
 313   }
 314
 315   /* Step 1: allocate and initialize JPEG decompression object */
 316
 317   /* We set up the normal JPEG error routines, then override error_exit. */
 318   cinfo.err = jpeg_std_error(&jerr.pub);
 319   jerr.pub.error_exit = my_error_exit;
 320   /* Establish the setjmp return context for my_error_exit to use. */
 321   if (setjmp(jerr.setjmp_buffer)) {
 322     /* If we get here, the JPEG code has signaled an error.
 323      * We need to clean up the JPEG object, close the input file, and return.
 324      */
 325     jpeg_destroy_decompress(&cinfo);
 326     fclose(infile);
 327     return 0;
 328   }
 329   /* Now we can initialize the JPEG decompression object. */
 330   jpeg_create_decompress(&cinfo);
 331
 332   /* Step 2: specify data source (eg, a file) */
 333
 334   jpeg_stdio_src(&cinfo, infile);
 335
 336   /* Step 3: read file parameters with jpeg_read_header() */
 337
 338   (void) jpeg_read_header(&cinfo, TRUE);
 339   /* We can ignore the return value from jpeg_read_header since
 340    *   (a) suspension is not possible with the stdio data source, and
 341    *   (b) we passed TRUE to reject a tables-only JPEG file as an error.
 342    * See libjpeg.doc for more info.
 343    */
 344
 345   /* Step 4: set parameters for decompression */
 346
 347   /* In this example, we don't need to change any of the defaults set by
 348    * jpeg_read_header(), so we do nothing here.
 349    */
 350
 351   /* Step 5: Start decompressor */
 352
 353   (void) jpeg_start_decompress(&cinfo);
 354   /* We can ignore the return value since suspension is not possible
 355    * with the stdio data source.
 356    */
 357
 358   /* We may need to do some setup of our own at this point before reading
 359    * the data.  After jpeg_start_decompress() we have the correct scaled
 360    * output image dimensions available, as well as the output colormap
 361    * if we asked for color quantization.
 362    * In this example, we need to make an output work buffer of the right size.
 363    */
 364   /* JSAMPLEs per row in output buffer */
 365   row_stride = cinfo.output_width * cinfo.output_components;
 366   /* Make a one-row-high sample array that will go away when done with image */
 367   buffer = (*cinfo.mem->alloc_sarray)
 368                 ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
 369
 370   /* Step 6: while (scan lines remain to be read) */
 371   /*           jpeg_read_scanlines(...); */
 372
 373   /* Here we use the library's state variable cinfo.output_scanline as the
 374    * loop counter, so that we don't have to keep track ourselves.
 375    */
 376   while (cinfo.output_scanline < cinfo.output_height) {
 377     /* jpeg_read_scanlines expects an array of pointers to scanlines.
 378      * Here the array is only one element long, but you could ask for
 379      * more than one scanline at a time if that's more convenient.
 380      */
 381     (void) jpeg_read_scanlines(&cinfo, buffer, 1);
 382     /* Assume put_scanline_someplace wants a pointer and sample count. */
 383     put_scanline_someplace(buffer[0], row_stride);
 384   }
 385
 386   /* Step 7: Finish decompression */
 387
 388   (void) jpeg_finish_decompress(&cinfo);
 389   /* We can ignore the return value since suspension is not possible
 390    * with the stdio data source.
 391    */
 392
 393   /* Step 8: Release JPEG decompression object */
 394
 395   /* This is an important step since it will release a good deal of memory. */
 396   jpeg_destroy_decompress(&cinfo);
 397
 398   /* After finish_decompress, we can close the input file.
 399    * Here we postpone it until after no more JPEG errors are possible,
 400    * so as to simplify the setjmp error logic above.  (Actually, I don't
 401    * think that jpeg_destroy can do an error exit, but why assume anything...)
 402    */
 403   fclose(infile);
 404
 405   /* At this point you may want to check to see whether any corrupt-data
 406    * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
 407    */
 408
 409   /* And we're done! */
 410   return 1;
 411 }
 412
 413
 414 /*
 415  * SOME FINE POINTS:
 416  *
 417  * In the above code, we ignored the return value of jpeg_read_scanlines,
 418  * which is the number of scanlines actually read.  We could get away with
 419  * this because we asked for only one line at a time and we weren't using
 420  * a suspending data source.  See libjpeg.doc for more info.
 421  *
 422  * We cheated a bit by calling alloc_sarray() after jpeg_start_decompress();
 423  * we should have done it beforehand to ensure that the space would be
 424  * counted against the JPEG max_memory setting.  In some systems the above
 425  * code would risk an out-of-memory error.  However, in general we don't
 426  * know the output image dimensions before jpeg_start_decompress(), unless we
 427  * call jpeg_calc_output_dimensions().  See libjpeg.doc for more about this.
 428  *
 429  * Scanlines are returned in the same order as they appear in the JPEG file,
 430  * which is standardly top-to-bottom.  If you must emit data bottom-to-top,
 431  * you can use one of the virtual arrays provided by the JPEG memory manager
 432  * to invert the data.  See wrbmp.c for an example.
 433  *
 434  * As with compression, some operating modes may require temporary files.
 435  * On some systems you may need to set up a signal handler to ensure that
 436  * temporary files are deleted if the program is interrupted.  See libjpeg.doc.
 437  */