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