media/libjpeg/jdmainct.c

   1 /*
   2  * jdmainct.c
   3  *
   4  * This file was part of the Independent JPEG Group's software:
   5  * Copyright (C) 1994-1996, Thomas G. Lane.
   6  * libjpeg-turbo Modifications:
   7  * Copyright (C) 2010, 2016, D. R. Commander.
   8  * For conditions of distribution and use, see the accompanying README.ijg
   9  * file.
  10  *
  11  * This file contains the main buffer controller for decompression.
  12  * The main buffer lies between the JPEG decompressor proper and the
  13  * post-processor; it holds downsampled data in the JPEG colorspace.
  14  *
  15  * Note that this code is bypassed in raw-data mode, since the application
  16  * supplies the equivalent of the main buffer in that case.
  17  */
  18
  19 #include "jinclude.h"
  20 #include "jdmainct.h"
  21 #include "jconfigint.h"
  22
  23
  24 /*
  25  * In the current system design, the main buffer need never be a full-image
  26  * buffer; any full-height buffers will be found inside the coefficient or
  27  * postprocessing controllers.  Nonetheless, the main controller is not
  28  * trivial.  Its responsibility is to provide context rows for upsampling/
  29  * rescaling, and doing this in an efficient fashion is a bit tricky.
  30  *
  31  * Postprocessor input data is counted in "row groups".  A row group
  32  * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
  33  * sample rows of each component.  (We require DCT_scaled_size values to be
  34  * chosen such that these numbers are integers.  In practice DCT_scaled_size
  35  * values will likely be powers of two, so we actually have the stronger
  36  * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
  37  * Upsampling will typically produce max_v_samp_factor pixel rows from each
  38  * row group (times any additional scale factor that the upsampler is
  39  * applying).
  40  *
  41  * The coefficient controller will deliver data to us one iMCU row at a time;
  42  * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
  43  * exactly min_DCT_scaled_size row groups.  (This amount of data corresponds
  44  * to one row of MCUs when the image is fully interleaved.)  Note that the
  45  * number of sample rows varies across components, but the number of row
  46  * groups does not.  Some garbage sample rows may be included in the last iMCU
  47  * row at the bottom of the image.
  48  *
  49  * Depending on the vertical scaling algorithm used, the upsampler may need
  50  * access to the sample row(s) above and below its current input row group.
  51  * The upsampler is required to set need_context_rows TRUE at global selection
  52  * time if so.  When need_context_rows is FALSE, this controller can simply
  53  * obtain one iMCU row at a time from the coefficient controller and dole it
  54  * out as row groups to the postprocessor.
  55  *
  56  * When need_context_rows is TRUE, this controller guarantees that the buffer
  57  * passed to postprocessing contains at least one row group's worth of samples
  58  * above and below the row group(s) being processed.  Note that the context
  59  * rows "above" the first passed row group appear at negative row offsets in
  60  * the passed buffer.  At the top and bottom of the image, the required
  61  * context rows are manufactured by duplicating the first or last real sample
  62  * row; this avoids having special cases in the upsampling inner loops.
  63  *
  64  * The amount of context is fixed at one row group just because that's a
  65  * convenient number for this controller to work with.  The existing
  66  * upsamplers really only need one sample row of context.  An upsampler
  67  * supporting arbitrary output rescaling might wish for more than one row
  68  * group of context when shrinking the image; tough, we don't handle that.
  69  * (This is justified by the assumption that downsizing will be handled mostly
  70  * by adjusting the DCT_scaled_size values, so that the actual scale factor at
  71  * the upsample step needn't be much less than one.)
  72  *
  73  * To provide the desired context, we have to retain the last two row groups
  74  * of one iMCU row while reading in the next iMCU row.  (The last row group
  75  * can't be processed until we have another row group for its below-context,
  76  * and so we have to save the next-to-last group too for its above-context.)
  77  * We could do this most simply by copying data around in our buffer, but
  78  * that'd be very slow.  We can avoid copying any data by creating a rather
  79  * strange pointer structure.  Here's how it works.  We allocate a workspace
  80  * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
  81  * of row groups per iMCU row).  We create two sets of redundant pointers to
  82  * the workspace.  Labeling the physical row groups 0 to M+1, the synthesized
  83  * pointer lists look like this:
  84  *                   M+1                          M-1
  85  * master pointer --> 0         master pointer --> 0
  86  *                    1                            1
  87  *                   ...                          ...
  88  *                   M-3                          M-3
  89  *                   M-2                           M
  90  *                   M-1                          M+1
  91  *                    M                           M-2
  92  *                   M+1                          M-1
  93  *                    0                            0
  94  * We read alternate iMCU rows using each master pointer; thus the last two
  95  * row groups of the previous iMCU row remain un-overwritten in the workspace.
  96  * The pointer lists are set up so that the required context rows appear to
  97  * be adjacent to the proper places when we pass the pointer lists to the
  98  * upsampler.
  99  *
 100  * The above pictures describe the normal state of the pointer lists.
 101  * At top and bottom of the image, we diddle the pointer lists to duplicate
 102  * the first or last sample row as necessary (this is cheaper than copying
 103  * sample rows around).
 104  *
 105  * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1.  In that
 106  * situation each iMCU row provides only one row group so the buffering logic
 107  * must be different (eg, we must read two iMCU rows before we can emit the
 108  * first row group).  For now, we simply do not support providing context
 109  * rows when min_DCT_scaled_size is 1.  That combination seems unlikely to
 110  * be worth providing --- if someone wants a 1/8th-size preview, they probably
 111  * want it quick and dirty, so a context-free upsampler is sufficient.
 112  */
 113
 114
 115 /* Forward declarations */
 116 METHODDEF(void) process_data_simple_main(j_decompress_ptr cinfo,
 117                                          JSAMPARRAY output_buf,
 118                                          JDIMENSION *out_row_ctr,
 119                                          JDIMENSION out_rows_avail);
 120 METHODDEF(void) process_data_context_main(j_decompress_ptr cinfo,
 121                                           JSAMPARRAY output_buf,
 122                                           JDIMENSION *out_row_ctr,
 123                                           JDIMENSION out_rows_avail);
 124 #ifdef QUANT_2PASS_SUPPORTED
 125 METHODDEF(void) process_data_crank_post(j_decompress_ptr cinfo,
 126                                         JSAMPARRAY output_buf,
 127                                         JDIMENSION *out_row_ctr,
 128                                         JDIMENSION out_rows_avail);
 129 #endif
 130
 131
 132 LOCAL(void)
 133 alloc_funny_pointers(j_decompress_ptr cinfo)
 134 /* Allocate space for the funny pointer lists.
 135  * This is done only once, not once per pass.
 136  */
 137 {
 138   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
 139   int ci, rgroup;
 140   int M = cinfo->_min_DCT_scaled_size;
 141   jpeg_component_info *compptr;
 142   JSAMPARRAY xbuf;
 143
 144   /* Get top-level space for component array pointers.
 145    * We alloc both arrays with one call to save a few cycles.
 146    */
 147   main_ptr->xbuffer[0] = (JSAMPIMAGE)
 148     (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
 149                                 cinfo->num_components * 2 * sizeof(JSAMPARRAY));
 150   main_ptr->xbuffer[1] = main_ptr->xbuffer[0] + cinfo->num_components;
 151
 152   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 153        ci++, compptr++) {
 154     rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
 155       cinfo->_min_DCT_scaled_size; /* height of a row group of component */
 156     /* Get space for pointer lists --- M+4 row groups in each list.
 157      * We alloc both pointer lists with one call to save a few cycles.
 158      */
 159     xbuf = (JSAMPARRAY)
 160       (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
 161                                   2 * (rgroup * (M + 4)) * sizeof(JSAMPROW));
 162     xbuf += rgroup;             /* want one row group at negative offsets */
 163     main_ptr->xbuffer[0][ci] = xbuf;
 164     xbuf += rgroup * (M + 4);
 165     main_ptr->xbuffer[1][ci] = xbuf;
 166   }
 167 }
 168
 169
 170 LOCAL(void)
 171 make_funny_pointers(j_decompress_ptr cinfo)
 172 /* Create the funny pointer lists discussed in the comments above.
 173  * The actual workspace is already allocated (in main_ptr->buffer),
 174  * and the space for the pointer lists is allocated too.
 175  * This routine just fills in the curiously ordered lists.
 176  * This will be repeated at the beginning of each pass.
 177  */
 178 {
 179   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
 180   int ci, i, rgroup;
 181   int M = cinfo->_min_DCT_scaled_size;
 182   jpeg_component_info *compptr;
 183   JSAMPARRAY buf, xbuf0, xbuf1;
 184
 185   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 186        ci++, compptr++) {
 187     rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
 188       cinfo->_min_DCT_scaled_size; /* height of a row group of component */
 189     xbuf0 = main_ptr->xbuffer[0][ci];
 190     xbuf1 = main_ptr->xbuffer[1][ci];
 191     /* First copy the workspace pointers as-is */
 192     buf = main_ptr->buffer[ci];
 193     for (i = 0; i < rgroup * (M + 2); i++) {
 194       xbuf0[i] = xbuf1[i] = buf[i];
 195     }
 196     /* In the second list, put the last four row groups in swapped order */
 197     for (i = 0; i < rgroup * 2; i++) {
 198       xbuf1[rgroup * (M - 2) + i] = buf[rgroup * M + i];
 199       xbuf1[rgroup * M + i] = buf[rgroup * (M - 2) + i];
 200     }
 201     /* The wraparound pointers at top and bottom will be filled later
 202      * (see set_wraparound_pointers, below).  Initially we want the "above"
 203      * pointers to duplicate the first actual data line.  This only needs
 204      * to happen in xbuffer[0].
 205      */
 206     for (i = 0; i < rgroup; i++) {
 207       xbuf0[i - rgroup] = xbuf0[0];
 208     }
 209   }
 210 }
 211
 212
 213 LOCAL(void)
 214 set_bottom_pointers(j_decompress_ptr cinfo)
 215 /* Change the pointer lists to duplicate the last sample row at the bottom
 216  * of the image.  whichptr indicates which xbuffer holds the final iMCU row.
 217  * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
 218  */
 219 {
 220   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
 221   int ci, i, rgroup, iMCUheight, rows_left;
 222   jpeg_component_info *compptr;
 223   JSAMPARRAY xbuf;
 224
 225   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 226        ci++, compptr++) {
 227     /* Count sample rows in one iMCU row and in one row group */
 228     iMCUheight = compptr->v_samp_factor * compptr->_DCT_scaled_size;
 229     rgroup = iMCUheight / cinfo->_min_DCT_scaled_size;
 230     /* Count nondummy sample rows remaining for this component */
 231     rows_left = (int)(compptr->downsampled_height % (JDIMENSION)iMCUheight);
 232     if (rows_left == 0) rows_left = iMCUheight;
 233     /* Count nondummy row groups.  Should get same answer for each component,
 234      * so we need only do it once.
 235      */
 236     if (ci == 0) {
 237       main_ptr->rowgroups_avail = (JDIMENSION)((rows_left - 1) / rgroup + 1);
 238     }
 239     /* Duplicate the last real sample row rgroup*2 times; this pads out the
 240      * last partial rowgroup and ensures at least one full rowgroup of context.
 241      */
 242     xbuf = main_ptr->xbuffer[main_ptr->whichptr][ci];
 243     for (i = 0; i < rgroup * 2; i++) {
 244       xbuf[rows_left + i] = xbuf[rows_left - 1];
 245     }
 246   }
 247 }
 248
 249
 250 /*
 251  * Initialize for a processing pass.
 252  */
 253
 254 METHODDEF(void)
 255 start_pass_main(j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
 256 {
 257   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
 258
 259   switch (pass_mode) {
 260   case JBUF_PASS_THRU:
 261     if (cinfo->upsample->need_context_rows) {
 262       main_ptr->pub.process_data = process_data_context_main;
 263       make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
 264       main_ptr->whichptr = 0;   /* Read first iMCU row into xbuffer[0] */
 265       main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
 266       main_ptr->iMCU_row_ctr = 0;
 267     } else {
 268       /* Simple case with no context needed */
 269       main_ptr->pub.process_data = process_data_simple_main;
 270     }
 271     main_ptr->buffer_full = FALSE;      /* Mark buffer empty */
 272     main_ptr->rowgroup_ctr = 0;
 273     break;
 274 #ifdef QUANT_2PASS_SUPPORTED
 275   case JBUF_CRANK_DEST:
 276     /* For last pass of 2-pass quantization, just crank the postprocessor */
 277     main_ptr->pub.process_data = process_data_crank_post;
 278     break;
 279 #endif
 280   default:
 281     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
 282     break;
 283   }
 284 }
 285
 286
 287 /*
 288  * Process some data.
 289  * This handles the simple case where no context is required.
 290  */
 291
 292 METHODDEF(void)
 293 process_data_simple_main(j_decompress_ptr cinfo, JSAMPARRAY output_buf,
 294                          JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
 295 {
 296   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
 297   JDIMENSION rowgroups_avail;
 298
 299   /* Read input data if we haven't filled the main buffer yet */
 300   if (!main_ptr->buffer_full) {
 301     if (!(*cinfo->coef->decompress_data) (cinfo, main_ptr->buffer))
 302       return;                   /* suspension forced, can do nothing more */
 303     main_ptr->buffer_full = TRUE;       /* OK, we have an iMCU row to work with */
 304   }
 305
 306   /* There are always min_DCT_scaled_size row groups in an iMCU row. */
 307   rowgroups_avail = (JDIMENSION)cinfo->_min_DCT_scaled_size;
 308   /* Note: at the bottom of the image, we may pass extra garbage row groups
 309    * to the postprocessor.  The postprocessor has to check for bottom
 310    * of image anyway (at row resolution), so no point in us doing it too.
 311    */
 312
 313   /* Feed the postprocessor */
 314   (*cinfo->post->post_process_data) (cinfo, main_ptr->buffer,
 315                                      &main_ptr->rowgroup_ctr, rowgroups_avail,
 316                                      output_buf, out_row_ctr, out_rows_avail);
 317
 318   /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
 319   if (main_ptr->rowgroup_ctr >= rowgroups_avail) {
 320     main_ptr->buffer_full = FALSE;
 321     main_ptr->rowgroup_ctr = 0;
 322   }
 323 }
 324
 325
 326 /*
 327  * Process some data.
 328  * This handles the case where context rows must be provided.
 329  */
 330
 331 METHODDEF(void)
 332 process_data_context_main(j_decompress_ptr cinfo, JSAMPARRAY output_buf,
 333                           JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
 334 {
 335   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
 336
 337   /* Read input data if we haven't filled the main buffer yet */
 338   if (!main_ptr->buffer_full) {
 339     if (!(*cinfo->coef->decompress_data) (cinfo,
 340                                           main_ptr->xbuffer[main_ptr->whichptr]))
 341       return;                   /* suspension forced, can do nothing more */
 342     main_ptr->buffer_full = TRUE;       /* OK, we have an iMCU row to work with */
 343     main_ptr->iMCU_row_ctr++;   /* count rows received */
 344   }
 345
 346   /* Postprocessor typically will not swallow all the input data it is handed
 347    * in one call (due to filling the output buffer first).  Must be prepared
 348    * to exit and restart.  This switch lets us keep track of how far we got.
 349    * Note that each case falls through to the next on successful completion.
 350    */
 351   switch (main_ptr->context_state) {
 352   case CTX_POSTPONED_ROW:
 353     /* Call postprocessor using previously set pointers for postponed row */
 354     (*cinfo->post->post_process_data) (cinfo,
 355                                        main_ptr->xbuffer[main_ptr->whichptr],
 356                                        &main_ptr->rowgroup_ctr,
 357                                        main_ptr->rowgroups_avail, output_buf,
 358                                        out_row_ctr, out_rows_avail);
 359     if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)
 360       return;                   /* Need to suspend */
 361     main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
 362     if (*out_row_ctr >= out_rows_avail)
 363       return;                   /* Postprocessor exactly filled output buf */
 364     FALLTHROUGH                 /*FALLTHROUGH*/
 365   case CTX_PREPARE_FOR_IMCU:
 366     /* Prepare to process first M-1 row groups of this iMCU row */
 367     main_ptr->rowgroup_ctr = 0;
 368     main_ptr->rowgroups_avail = (JDIMENSION)(cinfo->_min_DCT_scaled_size - 1);
 369     /* Check for bottom of image: if so, tweak pointers to "duplicate"
 370      * the last sample row, and adjust rowgroups_avail to ignore padding rows.
 371      */
 372     if (main_ptr->iMCU_row_ctr == cinfo->total_iMCU_rows)
 373       set_bottom_pointers(cinfo);
 374     main_ptr->context_state = CTX_PROCESS_IMCU;
 375     FALLTHROUGH                 /*FALLTHROUGH*/
 376   case CTX_PROCESS_IMCU:
 377     /* Call postprocessor using previously set pointers */
 378     (*cinfo->post->post_process_data) (cinfo,
 379                                        main_ptr->xbuffer[main_ptr->whichptr],
 380                                        &main_ptr->rowgroup_ctr,
 381                                        main_ptr->rowgroups_avail, output_buf,
 382                                        out_row_ctr, out_rows_avail);
 383     if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)
 384       return;                   /* Need to suspend */
 385     /* After the first iMCU, change wraparound pointers to normal state */
 386     if (main_ptr->iMCU_row_ctr == 1)
 387       set_wraparound_pointers(cinfo);
 388     /* Prepare to load new iMCU row using other xbuffer list */
 389     main_ptr->whichptr ^= 1;    /* 0=>1 or 1=>0 */
 390     main_ptr->buffer_full = FALSE;
 391     /* Still need to process last row group of this iMCU row, */
 392     /* which is saved at index M+1 of the other xbuffer */
 393     main_ptr->rowgroup_ctr = (JDIMENSION)(cinfo->_min_DCT_scaled_size + 1);
 394     main_ptr->rowgroups_avail = (JDIMENSION)(cinfo->_min_DCT_scaled_size + 2);
 395     main_ptr->context_state = CTX_POSTPONED_ROW;
 396   }
 397 }
 398
 399
 400 /*
 401  * Process some data.
 402  * Final pass of two-pass quantization: just call the postprocessor.
 403  * Source data will be the postprocessor controller's internal buffer.
 404  */
 405
 406 #ifdef QUANT_2PASS_SUPPORTED
 407
 408 METHODDEF(void)
 409 process_data_crank_post(j_decompress_ptr cinfo, JSAMPARRAY output_buf,
 410                         JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
 411 {
 412   (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE)NULL,
 413                                      (JDIMENSION *)NULL, (JDIMENSION)0,
 414                                      output_buf, out_row_ctr, out_rows_avail);
 415 }
 416
 417 #endif /* QUANT_2PASS_SUPPORTED */
 418
 419
 420 /*
 421  * Initialize main buffer controller.
 422  */
 423
 424 GLOBAL(void)
 425 jinit_d_main_controller(j_decompress_ptr cinfo, boolean need_full_buffer)
 426 {
 427   my_main_ptr main_ptr;
 428   int ci, rgroup, ngroups;
 429   jpeg_component_info *compptr;
 430
 431   main_ptr = (my_main_ptr)
 432     (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
 433                                 sizeof(my_main_controller));
 434   cinfo->main = (struct jpeg_d_main_controller *)main_ptr;
 435   main_ptr->pub.start_pass = start_pass_main;
 436
 437   if (need_full_buffer)         /* shouldn't happen */
 438     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
 439
 440   /* Allocate the workspace.
 441    * ngroups is the number of row groups we need.
 442    */
 443   if (cinfo->upsample->need_context_rows) {
 444     if (cinfo->_min_DCT_scaled_size < 2) /* unsupported, see comments above */
 445       ERREXIT(cinfo, JERR_NOTIMPL);
 446     alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
 447     ngroups = cinfo->_min_DCT_scaled_size + 2;
 448   } else {
 449     ngroups = cinfo->_min_DCT_scaled_size;
 450   }
 451
 452   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 453        ci++, compptr++) {
 454     rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
 455       cinfo->_min_DCT_scaled_size; /* height of a row group of component */
 456     main_ptr->buffer[ci] = (*cinfo->mem->alloc_sarray)
 457                         ((j_common_ptr)cinfo, JPOOL_IMAGE,
 458                          compptr->width_in_blocks * compptr->_DCT_scaled_size,
 459                          (JDIMENSION)(rgroup * ngroups));
 460   }
 461 }