images/io-libjpeg.c

   1 /*
   2  *      Image Library -- libjpeg
   3  *
   4  *      (c) 2006 Pavel Charvat <pchar@ucw.cz>
   5  *
   6  *      This software may be freely distributed and used according to the terms
   7  *      of the GNU Lesser General Public License.
   8  */
   9
  10 #undef LOCAL_DEBUG
  11
  12 #include "lib/lib.h"
  13 #include "lib/mempool.h"
  14 #include "lib/fastbuf.h"
  15 #include "images/images.h"
  16 #include "images/error.h"
  17 #include "images/color.h"
  18 #include "images/io-main.h"
  19
  20 #include <stdio.h>
  21 #include <sys/types.h>
  22 #include <jpeglib.h>
  23 #include <jerror.h>
  24 #include <setjmp.h>
  25
  26 struct libjpeg_err {
  27   struct jpeg_error_mgr pub;
  28   jmp_buf setjmp_buf;
  29   struct image_io *io;
  30 };
  31
  32 struct libjpeg_read_internals {
  33   struct jpeg_decompress_struct cinfo;
  34   struct jpeg_source_mgr src;
  35   struct libjpeg_err err;
  36   struct fastbuf *fastbuf;
  37   byte *fastbuf_pos;
  38 };
  39
  40 struct libjpeg_write_internals {
  41   struct jpeg_compress_struct cinfo;
  42   struct jpeg_destination_mgr dest;
  43   struct libjpeg_err err;
  44   struct fastbuf *fastbuf;
  45   byte *fastbuf_pos;
  46 };
  47
  48 static void NONRET
  49 libjpeg_read_error_exit(j_common_ptr cinfo)
  50 {
  51   DBG("libjpeg_error_exit()");
  52   struct libjpeg_err *e = (struct libjpeg_err *)cinfo->err;
  53   byte buf[JMSG_LENGTH_MAX];
  54   e->pub.format_message(cinfo, buf);
  55   IMAGE_ERROR(e->io->context, IMAGE_ERROR_READ_FAILED, "libjpeg: %s", buf);
  56   longjmp(e->setjmp_buf, 1);
  57 }
  58
  59 static void NONRET
  60 libjpeg_write_error_exit(j_common_ptr cinfo)
  61 {
  62   DBG("libjpeg_error_exit()");
  63   struct libjpeg_err *e = (struct libjpeg_err *)cinfo->err;
  64   byte buf[JMSG_LENGTH_MAX];
  65   e->pub.format_message(cinfo, buf);
  66   IMAGE_ERROR(e->io->context, IMAGE_ERROR_WRITE_FAILED, "libjpeg: %s", buf);
  67   longjmp(e->setjmp_buf, 1);
  68 }
  69
  70 static void
  71 libjpeg_emit_message(j_common_ptr cinfo UNUSED, int msg_level UNUSED)
  72 {
  73 #ifdef LOCAL_DEBUG
  74   byte buf[JMSG_LENGTH_MAX];
  75   cinfo->err->format_message(cinfo, buf);
  76   DBG("libjpeg_emit_message(): [%d] %s", msg_level, buf);
  77 #endif
  78 #if 0
  79   // Terminate on warning?
  80   if (unlikely(msg_level == -1))
  81     {
  82       struct libjpeg_err *e = (struct libjpeg_err *)cinfo->err;
  83       byte buf[JMSG_LENGTH_MAX];
  84       cinfo->err->format_message(cinfo, buf);
  85       IMAGE_ERROR(e->io->context, 0, "libjpeg: %s", buf);
  86       longjmp(e->setjmp_buf, 1);
  87     }
  88 #endif
  89 }
  90
  91 static inline uns
  92 libjpeg_fastbuf_read_prepare(struct libjpeg_read_internals *i)
  93 {
  94   DBG("libjpeg_fb_read_prepare()");
  95   byte *start;
  96   uns len = bdirect_read_prepare(i->fastbuf, &start);
  97   DBG("readed %u bytes at %p", len, start);
  98   if (!len)
  99     {
 100       // XXX: maybe only generate a warning and return EOI markers to recover from such errors (also in skip_input_data)
 101       IMAGE_ERROR(i->err.io->context, IMAGE_ERROR_READ_FAILED, "Incomplete JPEG file");
 102       longjmp(i->err.setjmp_buf, 1);
 103     }
 104   i->fastbuf_pos = start + len;
 105   i->src.next_input_byte = start;
 106   i->src.bytes_in_buffer = len;
 107   return len;
 108 }
 109
 110 static inline void
 111 libjpeg_fastbuf_read_commit(struct libjpeg_read_internals *i)
 112 {
 113   DBG("libjpeg_fb_read_commit()");
 114   bdirect_read_commit(i->fastbuf, i->fastbuf_pos);
 115 }
 116
 117 static void
 118 libjpeg_init_source(j_decompress_ptr cinfo)
 119 {
 120   DBG("libjpeg_init_source()");
 121   libjpeg_fastbuf_read_prepare((struct libjpeg_read_internals *)cinfo);
 122 }
 123
 124 static void
 125 libjpeg_term_source(j_decompress_ptr cinfo UNUSED)
 126 {
 127   DBG("libjpeg_term_source()");
 128   //libjpeg_fastbuf_read_commit((struct libjpeg_read_internals *)cinfo);
 129 }
 130
 131 static boolean
 132 libjpeg_fill_input_buffer(j_decompress_ptr cinfo)
 133 {
 134   DBG("libjpeg_fill_input_buffer()");
 135   struct libjpeg_read_internals *i = (struct libjpeg_read_internals *)cinfo;
 136   libjpeg_fastbuf_read_commit(i);
 137   libjpeg_fastbuf_read_prepare(i);
 138   return 1;
 139 }
 140
 141 static void
 142 libjpeg_skip_input_data(j_decompress_ptr cinfo, long num_bytes)
 143 {
 144   DBG("libjpeg_skip_input_data(num_bytes=%d)", (int)num_bytes);
 145   if (num_bytes > 0)
 146     {
 147       struct libjpeg_read_internals *i = (struct libjpeg_read_internals *)cinfo;
 148       if ((unsigned long)num_bytes <= i->src.bytes_in_buffer)
 149         {
 150           i->src.next_input_byte += num_bytes;
 151           i->src.bytes_in_buffer -= num_bytes;
 152         }
 153       else
 154         {
 155           num_bytes -= i->src.bytes_in_buffer;
 156           libjpeg_fastbuf_read_commit(i);
 157           if (!bskip(i->fastbuf, num_bytes))
 158             {
 159               IMAGE_ERROR(i->err.io->context, IMAGE_ERROR_READ_FAILED, "Incomplete JPEG file");
 160               longjmp(i->err.setjmp_buf, 1);
 161             }
 162           libjpeg_fastbuf_read_prepare(i);
 163         }
 164     }
 165 }
 166
 167 static inline void
 168 libjpeg_fastbuf_write_prepare(struct libjpeg_write_internals *i)
 169 {
 170   byte *start;
 171   uns len = bdirect_write_prepare(i->fastbuf, &start);
 172   i->fastbuf_pos = start + len;
 173   i->dest.next_output_byte = start;
 174   i->dest.free_in_buffer = len;
 175   if (!len)
 176     {
 177       IMAGE_ERROR(i->err.io->context, IMAGE_ERROR_WRITE_FAILED, "Unexpected end of stream");
 178       longjmp(i->err.setjmp_buf, 1);
 179     }
 180 }
 181
 182 static void
 183 libjpeg_init_destination(j_compress_ptr cinfo)
 184 {
 185   DBG("libjpeg_init_destination()");
 186   libjpeg_fastbuf_write_prepare((struct libjpeg_write_internals *)cinfo);
 187 }
 188
 189 static void
 190 libjpeg_term_destination(j_compress_ptr cinfo)
 191 {
 192   DBG("libjpeg_term_destination()");
 193   struct libjpeg_write_internals *i = (struct libjpeg_write_internals *)cinfo;
 194   bdirect_write_commit(i->fastbuf, (byte *)i->dest.next_output_byte);
 195 }
 196
 197 static boolean
 198 libjpeg_empty_output_buffer(j_compress_ptr cinfo)
 199 {
 200   DBG("libjpeg_empty_output_buffer()");
 201   struct libjpeg_write_internals *i = (struct libjpeg_write_internals *)cinfo;
 202   bdirect_write_commit(i->fastbuf, i->fastbuf_pos);
 203   libjpeg_fastbuf_write_prepare(i);
 204   return TRUE;
 205 }
 206
 207 static inline uns
 208 libjpeg_read_byte(struct libjpeg_read_internals *i)
 209 {
 210   DBG("libjpeg_read_byte()");
 211   if (!i->src.bytes_in_buffer)
 212     if (!libjpeg_fill_input_buffer(&i->cinfo))
 213       ERREXIT(&i->cinfo, JERR_CANT_SUSPEND);
 214   i->src.bytes_in_buffer--;
 215   return *i->src.next_input_byte++;
 216 }
 217
 218 static inline void
 219 libjpeg_read_buf(struct libjpeg_read_internals *i, byte *buf, uns len)
 220 {
 221   DBG("libjpeg_read_buf(len=%u)", len);
 222   while (len)
 223     {
 224       if (!i->src.bytes_in_buffer)
 225         if (!libjpeg_fill_input_buffer(&i->cinfo))
 226           ERREXIT(&i->cinfo, JERR_CANT_SUSPEND);
 227       uns buf_size = i->src.bytes_in_buffer;
 228       uns read_size = MIN(buf_size, len);
 229       memcpy(buf, i->src.next_input_byte, read_size);
 230       i->src.bytes_in_buffer -= read_size;
 231       i->src.next_input_byte += read_size;
 232       len -= read_size;
 233     }
 234 }
 235
 236 static byte libjpeg_exif_header[6] = { 'E', 'x', 'i', 'f', 0, 0 };
 237
 238 static boolean
 239 libjpeg_app1_preprocessor(j_decompress_ptr cinfo)
 240 {
 241   struct libjpeg_read_internals *i = (struct libjpeg_read_internals *)cinfo;
 242   struct image_io *io = i->err.io;
 243   uns len = libjpeg_read_byte(i) << 8;
 244   len += libjpeg_read_byte(i);
 245   DBG("Found APP1 marker, len=%u", len);
 246   if (len < 2)
 247     return TRUE;
 248   len -= 2;
 249   if (len < 7 /*|| io->exif_size*/)
 250     {
 251       libjpeg_skip_input_data(cinfo, len);
 252       return TRUE;
 253     }
 254   byte header[6];
 255   libjpeg_read_buf(i, header, 6);
 256   if (memcmp(header, libjpeg_exif_header, 6))
 257     {
 258       libjpeg_skip_input_data(cinfo, len - 6);
 259       return TRUE;
 260     }
 261   io->exif_size = len;
 262   io->exif_data = mp_alloc(io->internal_pool, len);
 263   memcpy(io->exif_data, header, 6);
 264   libjpeg_read_buf(i, io->exif_data + 6, len - 6);
 265   DBG("Parsed EXIF of length %u", len);
 266   return TRUE;
 267 }
 268
 269 static void
 270 libjpeg_read_cancel(struct image_io *io)
 271 {
 272   DBG("libjpeg_read_cancel()");
 273   struct libjpeg_read_internals *i = io->read_data;
 274   jpeg_destroy_decompress(&i->cinfo);
 275 }
 276
 277 int
 278 libjpeg_read_header(struct image_io *io)
 279 {
 280   DBG("libjpeg_read_header()");
 281   struct libjpeg_read_internals *i = io->read_data = mp_alloc(io->internal_pool, sizeof(*i));
 282   i->fastbuf = io->fastbuf;
 283
 284   /* Create libjpeg read structure */
 285   DBG("Creating libjpeg read structure");
 286   i->cinfo.err = jpeg_std_error(&i->err.pub);
 287   i->err.pub.error_exit = libjpeg_read_error_exit;
 288   i->err.pub.emit_message = libjpeg_emit_message;
 289   i->err.io = io;
 290   if (setjmp(i->err.setjmp_buf))
 291     {
 292       DBG("Libjpeg failed to read the image, longjump saved us");
 293       jpeg_destroy_decompress(&i->cinfo);
 294       return 0;
 295     }
 296   jpeg_create_decompress(&i->cinfo);
 297
 298   /* Initialize source manager */
 299   i->cinfo.src = &i->src;
 300   i->src.init_source = libjpeg_init_source;
 301   i->src.fill_input_buffer = libjpeg_fill_input_buffer;
 302   i->src.skip_input_data = libjpeg_skip_input_data;
 303   i->src.resync_to_restart = jpeg_resync_to_restart;
 304   i->src.term_source = libjpeg_term_source;
 305
 306   if (io->flags & IMAGE_IO_WANT_EXIF)
 307     jpeg_set_marker_processor(&i->cinfo, JPEG_APP0 + 1, libjpeg_app1_preprocessor);
 308
 309   /* Read JPEG header and setup decompression options */
 310   DBG("Reading image header");
 311   jpeg_read_header(&i->cinfo, TRUE);
 312   switch (i->cinfo.jpeg_color_space)
 313     {
 314       case JCS_GRAYSCALE:
 315         io->flags = COLOR_SPACE_GRAYSCALE;
 316         break;
 317       case JCS_RGB:
 318         io->flags = COLOR_SPACE_RGB;
 319         break;
 320       case JCS_YCbCr:
 321         io->flags = COLOR_SPACE_YCBCR;
 322         break;
 323       case JCS_CMYK:
 324         io->flags = COLOR_SPACE_CMYK;
 325         break;
 326       case JCS_YCCK:
 327         io->flags = COLOR_SPACE_YCCK;
 328         break;
 329       default:
 330         if (unlikely(i->cinfo.num_components < 1 || i->cinfo.num_components > 4))
 331           {
 332             jpeg_destroy_decompress(&i->cinfo);
 333             IMAGE_ERROR(io->context, IMAGE_ERROR_INVALID_PIXEL_FORMAT, "Invalid color space.");
 334             return 0;
 335           }
 336         io->flags = COLOR_SPACE_UNKNOWN + i->cinfo.num_components;
 337         break;
 338     }
 339   if (unlikely(i->cinfo.num_components != (int)color_space_channels[io->flags]))
 340     {
 341       jpeg_destroy_decompress(&i->cinfo);
 342       IMAGE_ERROR(io->context, IMAGE_ERROR_INVALID_PIXEL_FORMAT, "Invalid number of color channels.");
 343       return 0;
 344     }
 345   io->cols = i->cinfo.image_width;
 346   io->rows = i->cinfo.image_height;
 347   io->number_of_colors = (i->cinfo.num_components < 4) ? (1U << (i->cinfo.num_components * 8)) : 0xffffffff;
 348   io->read_cancel = libjpeg_read_cancel;
 349   return 1;
 350 }
 351
 352 int
 353 libjpeg_read_data(struct image_io *io)
 354 {
 355   DBG("libjpeg_read_data()");
 356
 357   struct libjpeg_read_internals *i = io->read_data;
 358   uns read_flags = io->flags;
 359
 360   /* Select color space */
 361   switch (read_flags & IMAGE_COLOR_SPACE)
 362     {
 363       case COLOR_SPACE_GRAYSCALE:
 364         i->cinfo.out_color_space = JCS_GRAYSCALE;
 365         break;
 366       case COLOR_SPACE_YCBCR:
 367         i->cinfo.out_color_space = JCS_YCbCr;
 368         break;
 369       case COLOR_SPACE_CMYK:
 370         i->cinfo.out_color_space = JCS_CMYK;
 371         break;
 372       case COLOR_SPACE_YCCK:
 373         i->cinfo.out_color_space = JCS_YCCK;
 374         break;
 375       default:
 376         switch (i->cinfo.jpeg_color_space)
 377           {
 378             case JCS_CMYK:
 379               read_flags = (read_flags & ~IMAGE_COLOR_SPACE & IMAGE_CHANNELS_FORMAT) | COLOR_SPACE_CMYK;
 380               i->cinfo.out_color_space = JCS_CMYK;
 381               break;
 382             case JCS_YCCK:
 383               read_flags = (read_flags & ~IMAGE_COLOR_SPACE & IMAGE_CHANNELS_FORMAT) | COLOR_SPACE_YCCK;
 384               i->cinfo.out_color_space = JCS_YCCK;
 385               break;
 386             default:
 387               read_flags = (read_flags & ~IMAGE_COLOR_SPACE & IMAGE_CHANNELS_FORMAT) | COLOR_SPACE_RGB;
 388               i->cinfo.out_color_space = JCS_RGB;
 389               break;
 390           }
 391         break;
 392     }
 393
 394   /* Prepare the image  */
 395   struct image_io_read_data_internals rdi;
 396   if (io->cols <= (i->cinfo.image_width >> 3) && io->rows <= (i->cinfo.image_height >> 3))
 397     {
 398       DBG("Scaling to 1/8");
 399       i->cinfo.scale_num = 1;
 400       i->cinfo.scale_denom = 8;
 401     }
 402   else if (io->cols <= (i->cinfo.image_width >> 2) && io->rows <= (i->cinfo.image_height >> 2))
 403     {
 404       DBG("Scaling to 1/4");
 405       i->cinfo.scale_num = 1;
 406       i->cinfo.scale_denom = 4;
 407     }
 408   else if (io->cols <= (i->cinfo.image_width >> 1) && io->rows <= (i->cinfo.image_height >> 1))
 409     {
 410       DBG("Scaling to 1/2");
 411       i->cinfo.scale_num = 1;
 412       i->cinfo.scale_denom = 2;
 413     }
 414   jpeg_calc_output_dimensions(&i->cinfo);
 415   DBG("Output dimensions %ux%u", (uns)i->cinfo.output_width, (uns)i->cinfo.output_height);
 416   if (unlikely(!image_io_read_data_prepare(&rdi, io, i->cinfo.output_width, i->cinfo.output_height, read_flags)))
 417     {
 418       jpeg_destroy_decompress(&i->cinfo);
 419       return 0;
 420     }
 421
 422   /* Setup fallback */
 423   if (setjmp(i->err.setjmp_buf))
 424     {
 425       DBG("Libjpeg failed to read the image, longjump saved us");
 426       jpeg_destroy_decompress(&i->cinfo);
 427       image_io_read_data_break(&rdi, io);
 428       return 0;
 429     }
 430
 431   /* Decompress the image */
 432   struct image *img = rdi.image;
 433   jpeg_start_decompress(&i->cinfo);
 434   if ((int)img->pixel_size == i->cinfo.output_components)
 435     {
 436       byte *pixels = img->pixels;
 437       for (uns r = img->rows; r--; )
 438         {
 439           jpeg_read_scanlines(&i->cinfo, (JSAMPLE **)&pixels, 1);
 440           pixels += img->row_size;
 441         }
 442     }
 443   else
 444     {
 445       switch (img->pixel_size)
 446         {
 447           case 2: /* Grayscale -> Grayscale+Alpha */
 448             {
 449               ASSERT(i->cinfo.output_components == 1);
 450               byte buf[img->cols], *src;
 451 #             define IMAGE_WALK_PREFIX(x) walk_##x
 452 #             define IMAGE_WALK_INLINE
 453 #             define IMAGE_WALK_IMAGE img
 454 #             define IMAGE_WALK_UNROLL 4
 455 #             define IMAGE_WALK_COL_STEP 2
 456 #             define IMAGE_WALK_DO_ROW_START do{ src = buf; jpeg_read_scanlines(&i->cinfo, (JSAMPLE **)&src, 1); }while(0)
 457 #             define IMAGE_WALK_DO_STEP do{ walk_pos[0] = *src++; walk_pos[1] = 255; }while(0)
 458 #             include "images/image-walk.h"
 459             }
 460             break;
 461           case 4: /* * -> *+Alpha or aligned * */
 462             {
 463               ASSERT(i->cinfo.output_components == 3);
 464               byte buf[img->cols * 3], *src;
 465 #             define IMAGE_WALK_PREFIX(x) walk_##x
 466 #             define IMAGE_WALK_INLINE
 467 #             define IMAGE_WALK_IMAGE img
 468 #             define IMAGE_WALK_UNROLL 4
 469 #             define IMAGE_WALK_COL_STEP 4
 470 #             define IMAGE_WALK_DO_ROW_START do{ src = buf; jpeg_read_scanlines(&i->cinfo, (JSAMPLE **)&src, 1); }while(0)
 471 #             define IMAGE_WALK_DO_STEP do{ *(u32 *)walk_pos = *(u32 *)src; walk_pos[3] = 255; src += 3; }while(0)
 472 #             include "images/image-walk.h"
 473             }
 474             break;
 475           default:
 476             ASSERT(0);
 477         }
 478
 479     }
 480
 481   ASSERT(i->cinfo.output_scanline == i->cinfo.output_height);
 482
 483   /* Destroy libjpeg object */
 484   jpeg_finish_decompress(&i->cinfo);
 485   jpeg_destroy_decompress(&i->cinfo);
 486
 487   /* Finish the image */
 488   return image_io_read_data_finish(&rdi, io);
 489 }
 490
 491 int
 492 libjpeg_write(struct image_io *io)
 493 {
 494   DBG("libjpeg_write()");
 495   struct libjpeg_write_internals i;
 496   i.fastbuf = io->fastbuf;
 497
 498   /* Create libjpeg write structure */
 499   DBG("Creating libjpeg write structure");
 500   i.cinfo.err = jpeg_std_error(&i.err.pub);
 501   i.err.pub.error_exit = libjpeg_write_error_exit;
 502   i.err.pub.emit_message = libjpeg_emit_message;
 503   i.err.io = io;
 504   if (setjmp(i.err.setjmp_buf))
 505     {
 506       DBG("Libjpeg failed to write the image, longjump saved us");
 507       jpeg_destroy_compress(&i.cinfo);
 508       return 0;
 509     }
 510   jpeg_create_compress(&i.cinfo);
 511
 512   /* Initialize destination manager */
 513   i.cinfo.dest = &i.dest;
 514   i.dest.init_destination = libjpeg_init_destination;
 515   i.dest.term_destination = libjpeg_term_destination;
 516   i.dest.empty_output_buffer = libjpeg_empty_output_buffer;
 517
 518   /* Set output parameters */
 519   struct image *img = io->image;
 520   i.cinfo.image_width = img->cols;
 521   i.cinfo.image_height = img->rows;
 522   switch (img->flags & IMAGE_COLOR_SPACE)
 523     {
 524       case COLOR_SPACE_GRAYSCALE:
 525         i.cinfo.in_color_space = JCS_GRAYSCALE;
 526         break;
 527       case COLOR_SPACE_RGB:
 528         i.cinfo.in_color_space = JCS_RGB;
 529         break;
 530       case COLOR_SPACE_YCBCR:
 531         i.cinfo.in_color_space = JCS_YCbCr;
 532         break;
 533       case COLOR_SPACE_CMYK:
 534         i.cinfo.in_color_space = JCS_CMYK;
 535         break;
 536       case COLOR_SPACE_YCCK:
 537         i.cinfo.in_color_space = JCS_YCCK;
 538         break;
 539       default:
 540         jpeg_destroy_compress(&i.cinfo);
 541         IMAGE_ERROR(io->context, IMAGE_ERROR_INVALID_PIXEL_FORMAT, "Unsupported pixel format.");
 542         return 0;
 543     }
 544   i.cinfo.input_components = color_space_channels[img->flags & IMAGE_COLOR_SPACE];
 545   jpeg_set_defaults(&i.cinfo);
 546   jpeg_set_colorspace(&i.cinfo, i.cinfo.in_color_space);
 547   if (io->jpeg_quality)
 548     jpeg_set_quality(&i.cinfo, MIN(io->jpeg_quality, 100), 1);
 549   if (io->exif_size)
 550     {
 551       /* According to the Exif specification, the Exif APP1 marker has to follow immediately after the SOI,
 552        * just as the JFIF specification requires the same for the JFIF APP0 marker!
 553        * Therefore a JPEG file cannot legally be both Exif and JFIF.  */
 554       i.cinfo.write_JFIF_header = FALSE;
 555       i.cinfo.write_Adobe_marker = FALSE;
 556     }
 557
 558   /* Compress the image */
 559   jpeg_start_compress(&i.cinfo, TRUE);
 560   if (io->exif_size)
 561     {
 562       DBG("Writing EXIF");
 563       jpeg_write_marker(&i.cinfo, JPEG_APP0 + 1, io->exif_data, io->exif_size);
 564     }
 565   if ((int)img->pixel_size == i.cinfo.input_components)
 566     {
 567       byte *pixels = img->pixels;
 568       for (uns r = img->rows; r--; )
 569         {
 570           jpeg_write_scanlines(&i.cinfo, (JSAMPLE **)&pixels, 1);
 571           pixels += img->row_size;
 572         }
 573     }
 574   else
 575     {
 576       switch (img->pixel_size)
 577         {
 578           case 2: /* Grayscale+Alpha -> Grayscale */
 579             {
 580               ASSERT(i.cinfo.input_components == 1);
 581               byte buf[img->cols], *dest = buf;
 582 #             define IMAGE_WALK_PREFIX(x) walk_##x
 583 #             define IMAGE_WALK_INLINE
 584 #             define IMAGE_WALK_IMAGE img
 585 #             define IMAGE_WALK_UNROLL 4
 586 #             define IMAGE_WALK_COL_STEP 2
 587 #             define IMAGE_WALK_DO_ROW_END do{ dest = buf; jpeg_write_scanlines(&i.cinfo, (JSAMPLE **)&dest, 1); }while(0)
 588 #             define IMAGE_WALK_DO_STEP do{ *dest++ = walk_pos[0]; }while(0)
 589 #             include "images/image-walk.h"
 590               break;
 591             }
 592           case 4: /* *+Alpha or aligned * -> * */
 593             {
 594               ASSERT(i.cinfo.input_components == 3);
 595               byte buf[img->cols * 3], *dest = buf;
 596 #             define IMAGE_WALK_PREFIX(x) walk_##x
 597 #             define IMAGE_WALK_INLINE
 598 #             define IMAGE_WALK_IMAGE img
 599 #             define IMAGE_WALK_UNROLL 4
 600 #             define IMAGE_WALK_COL_STEP 4
 601 #             define IMAGE_WALK_DO_ROW_END do{ dest = buf; jpeg_write_scanlines(&i.cinfo, (JSAMPLE **)&dest, 1); }while(0)
 602 #             define IMAGE_WALK_DO_STEP do{ *dest++ = walk_pos[0]; *dest++ = walk_pos[1]; *dest++ = walk_pos[2]; }while(0)
 603 #             include "images/image-walk.h"
 604               break;
 605             }
 606           default:
 607             ASSERT(0);
 608         }
 609     }
 610   ASSERT(i.cinfo.next_scanline == i.cinfo.image_height);
 611   jpeg_finish_compress(&i.cinfo);
 612   jpeg_destroy_compress(&i.cinfo);
 613   return 1;
 614 }