jdmainct.c (20645B)
1 /* 2 * jdmainct.c 3 * 4 * Copyright (C) 1994-1995, Thomas G. Lane. 5 * This file is part of the Independent JPEG Group's software. 6 * For conditions of distribution and use, see the accompanying README file. 7 * 8 * This file contains the main buffer controller for decompression. 9 * The main buffer lies between the JPEG decompressor proper and the 10 * post-processor; it holds downsampled data in the JPEG colorspace. 11 * 12 * Note that this code is bypassed in raw-data mode, since the application 13 * supplies the equivalent of the main buffer in that case. 14 */ 15 16 #define JPEG_INTERNALS 17 #include "jinclude.h" 18 #include "jpeglib.h" 19 20 21 /* 22 * In the current system design, the main buffer need never be a full-image 23 * buffer; any full-height buffers will be found inside the coefficient or 24 * postprocessing controllers. Nonetheless, the main controller is not 25 * trivial. Its responsibility is to provide context rows for upsampling/ 26 * rescaling, and doing this in an efficient fashion is a bit tricky. 27 * 28 * Postprocessor input data is counted in "row groups". A row group 29 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size) 30 * sample rows of each component. (We require DCT_scaled_size values to be 31 * chosen such that these numbers are integers. In practice DCT_scaled_size 32 * values will likely be powers of two, so we actually have the stronger 33 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.) 34 * Upsampling will typically produce max_v_samp_factor pixel rows from each 35 * row group (times any additional scale factor that the upsampler is 36 * applying). 37 * 38 * The coefficient controller will deliver data to us one iMCU row at a time; 39 * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or 40 * exactly min_DCT_scaled_size row groups. (This amount of data corresponds 41 * to one row of MCUs when the image is fully interleaved.) Note that the 42 * number of sample rows varies across components, but the number of row 43 * groups does not. Some garbage sample rows may be included in the last iMCU 44 * row at the bottom of the image. 45 * 46 * Depending on the vertical scaling algorithm used, the upsampler may need 47 * access to the sample row(s) above and below its current input row group. 48 * The upsampler is required to set need_context_rows TRUE at global selection 49 * time if so. When need_context_rows is FALSE, this controller can simply 50 * obtain one iMCU row at a time from the coefficient controller and dole it 51 * out as row groups to the postprocessor. 52 * 53 * When need_context_rows is TRUE, this controller guarantees that the buffer 54 * passed to postprocessing contains at least one row group's worth of samples 55 * above and below the row group(s) being processed. Note that the context 56 * rows "above" the first passed row group appear at negative row offsets in 57 * the passed buffer. At the top and bottom of the image, the required 58 * context rows are manufactured by duplicating the first or last real sample 59 * row; this avoids having special cases in the upsampling inner loops. 60 * 61 * The amount of context is fixed at one row group just because that's a 62 * convenient number for this controller to work with. The existing 63 * upsamplers really only need one sample row of context. An upsampler 64 * supporting arbitrary output rescaling might wish for more than one row 65 * group of context when shrinking the image; tough, we don't handle that. 66 * (This is justified by the assumption that downsizing will be handled mostly 67 * by adjusting the DCT_scaled_size values, so that the actual scale factor at 68 * the upsample step needn't be much less than one.) 69 * 70 * To provide the desired context, we have to retain the last two row groups 71 * of one iMCU row while reading in the next iMCU row. (The last row group 72 * can't be processed until we have another row group for its below-context, 73 * and so we have to save the next-to-last group too for its above-context.) 74 * We could do this most simply by copying data around in our buffer, but 75 * that'd be very slow. We can avoid copying any data by creating a rather 76 * strange pointer structure. Here's how it works. We allocate a workspace 77 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number 78 * of row groups per iMCU row). We create two sets of redundant pointers to 79 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized 80 * pointer lists look like this: 81 * M+1 M-1 82 * master pointer --> 0 master pointer --> 0 83 * 1 1 84 * ... ... 85 * M-3 M-3 86 * M-2 M 87 * M-1 M+1 88 * M M-2 89 * M+1 M-1 90 * 0 0 91 * We read alternate iMCU rows using each master pointer; thus the last two 92 * row groups of the previous iMCU row remain un-overwritten in the workspace. 93 * The pointer lists are set up so that the required context rows appear to 94 * be adjacent to the proper places when we pass the pointer lists to the 95 * upsampler. 96 * 97 * The above pictures describe the normal state of the pointer lists. 98 * At top and bottom of the image, we diddle the pointer lists to duplicate 99 * the first or last sample row as necessary (this is cheaper than copying 100 * sample rows around). 101 * 102 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that 103 * situation each iMCU row provides only one row group so the buffering logic 104 * must be different (eg, we must read two iMCU rows before we can emit the 105 * first row group). For now, we simply do not support providing context 106 * rows when min_DCT_scaled_size is 1. That combination seems unlikely to 107 * be worth providing --- if someone wants a 1/8th-size preview, they probably 108 * want it quick and dirty, so a context-free upsampler is sufficient. 109 */ 110 111 112 /* Private buffer controller object */ 113 114 typedef struct { 115 struct jpeg_d_main_controller pub; /* public fields */ 116 117 /* Pointer to allocated workspace (M or M+2 row groups). */ 118 JSAMPARRAY buffer[MAX_COMPONENTS]; 119 120 boolean buffer_full; /* Have we gotten an iMCU row from decoder? */ 121 JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */ 122 123 /* Remaining fields are only used in the context case. */ 124 125 /* These are the master pointers to the funny-order pointer lists. */ 126 JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */ 127 128 int whichptr; /* indicates which pointer set is now in use */ 129 int context_state; /* process_data state machine status */ 130 JDIMENSION rowgroups_avail; /* row groups available to postprocessor */ 131 JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */ 132 } my_main_controller; 133 134 typedef my_main_controller * my_main_ptr; 135 136 /* context_state values: */ 137 #define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */ 138 #define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */ 139 #define CTX_POSTPONED_ROW 2 /* feeding postponed row group */ 140 141 142 /* Forward declarations */ 143 METHODDEF void process_data_simple_main 144 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf, 145 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)); 146 METHODDEF void process_data_context_main 147 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf, 148 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)); 149 #ifdef QUANT_2PASS_SUPPORTED 150 METHODDEF void process_data_crank_post 151 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf, 152 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)); 153 #endif 154 155 156 LOCAL void 157 alloc_funny_pointers (j_decompress_ptr cinfo) 158 /* Allocate space for the funny pointer lists. 159 * This is done only once, not once per pass. 160 */ 161 { 162 // bk001204 - no use main 163 my_main_ptr jmain = (my_main_ptr) cinfo->main; 164 int ci, rgroup; 165 int M = cinfo->min_DCT_scaled_size; 166 jpeg_component_info *compptr; 167 JSAMPARRAY xbuf; 168 169 /* Get top-level space for component array pointers. 170 * We alloc both arrays with one call to save a few cycles. 171 */ 172 jmain->xbuffer[0] = (JSAMPIMAGE) 173 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 174 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY)); 175 jmain->xbuffer[1] = jmain->xbuffer[0] + cinfo->num_components; 176 177 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 178 ci++, compptr++) { 179 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 180 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 181 /* Get space for pointer lists --- M+4 row groups in each list. 182 * We alloc both pointer lists with one call to save a few cycles. 183 */ 184 xbuf = (JSAMPARRAY) 185 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 186 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW)); 187 xbuf += rgroup; /* want one row group at negative offsets */ 188 jmain->xbuffer[0][ci] = xbuf; 189 xbuf += rgroup * (M + 4); 190 jmain->xbuffer[1][ci] = xbuf; 191 } 192 } 193 194 195 LOCAL void 196 make_funny_pointers (j_decompress_ptr cinfo) 197 /* Create the funny pointer lists discussed in the comments above. 198 * The actual workspace is already allocated (in main->buffer), 199 * and the space for the pointer lists is allocated too. 200 * This routine just fills in the curiously ordered lists. 201 * This will be repeated at the beginning of each pass. 202 */ 203 { 204 // bk001204 - no use main 205 my_main_ptr jmain = (my_main_ptr) cinfo->main; 206 int ci, i, rgroup; 207 int M = cinfo->min_DCT_scaled_size; 208 jpeg_component_info *compptr; 209 JSAMPARRAY buf, xbuf0, xbuf1; 210 211 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 212 ci++, compptr++) { 213 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 214 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 215 xbuf0 = jmain->xbuffer[0][ci]; 216 xbuf1 = jmain->xbuffer[1][ci]; 217 /* First copy the workspace pointers as-is */ 218 buf = jmain->buffer[ci]; 219 for (i = 0; i < rgroup * (M + 2); i++) { 220 xbuf0[i] = xbuf1[i] = buf[i]; 221 } 222 /* In the second list, put the last four row groups in swapped order */ 223 for (i = 0; i < rgroup * 2; i++) { 224 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i]; 225 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i]; 226 } 227 /* The wraparound pointers at top and bottom will be filled later 228 * (see set_wraparound_pointers, below). Initially we want the "above" 229 * pointers to duplicate the first actual data line. This only needs 230 * to happen in xbuffer[0]. 231 */ 232 for (i = 0; i < rgroup; i++) { 233 xbuf0[i - rgroup] = xbuf0[0]; 234 } 235 } 236 } 237 238 239 LOCAL void 240 set_wraparound_pointers (j_decompress_ptr cinfo) 241 /* Set up the "wraparound" pointers at top and bottom of the pointer lists. 242 * This changes the pointer list state from top-of-image to the normal state. 243 */ 244 { 245 // bk001204 - no use main 246 my_main_ptr jmain = (my_main_ptr) cinfo->main; 247 int ci, i, rgroup; 248 int M = cinfo->min_DCT_scaled_size; 249 jpeg_component_info *compptr; 250 JSAMPARRAY xbuf0, xbuf1; 251 252 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 253 ci++, compptr++) { 254 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 255 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 256 xbuf0 = jmain->xbuffer[0][ci]; 257 xbuf1 = jmain->xbuffer[1][ci]; 258 for (i = 0; i < rgroup; i++) { 259 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i]; 260 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i]; 261 xbuf0[rgroup*(M+2) + i] = xbuf0[i]; 262 xbuf1[rgroup*(M+2) + i] = xbuf1[i]; 263 } 264 } 265 } 266 267 268 LOCAL void 269 set_bottom_pointers (j_decompress_ptr cinfo) 270 /* Change the pointer lists to duplicate the last sample row at the bottom 271 * of the image. whichptr indicates which xbuffer holds the final iMCU row. 272 * Also sets rowgroups_avail to indicate number of nondummy row groups in row. 273 */ 274 { 275 // bk001204 - no use main 276 my_main_ptr jmain = (my_main_ptr) cinfo->main; 277 int ci, i, rgroup, iMCUheight, rows_left; 278 jpeg_component_info *compptr; 279 JSAMPARRAY xbuf; 280 281 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 282 ci++, compptr++) { 283 /* Count sample rows in one iMCU row and in one row group */ 284 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size; 285 rgroup = iMCUheight / cinfo->min_DCT_scaled_size; 286 /* Count nondummy sample rows remaining for this component */ 287 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight); 288 if (rows_left == 0) rows_left = iMCUheight; 289 /* Count nondummy row groups. Should get same answer for each component, 290 * so we need only do it once. 291 */ 292 if (ci == 0) { 293 jmain->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1); 294 } 295 /* Duplicate the last real sample row rgroup*2 times; this pads out the 296 * last partial rowgroup and ensures at least one full rowgroup of context. 297 */ 298 xbuf = jmain->xbuffer[jmain->whichptr][ci]; 299 for (i = 0; i < rgroup * 2; i++) { 300 xbuf[rows_left + i] = xbuf[rows_left-1]; 301 } 302 } 303 } 304 305 306 /* 307 * Initialize for a processing pass. 308 */ 309 310 METHODDEF void 311 start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode) 312 { 313 // bk001204 - no use main 314 my_main_ptr jmain = (my_main_ptr) cinfo->main; 315 316 switch (pass_mode) { 317 case JBUF_PASS_THRU: 318 if (cinfo->upsample->need_context_rows) { 319 jmain->pub.process_data = process_data_context_main; 320 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */ 321 jmain->whichptr = 0; /* Read first iMCU row into xbuffer[0] */ 322 jmain->context_state = CTX_PREPARE_FOR_IMCU; 323 jmain->iMCU_row_ctr = 0; 324 } else { 325 /* Simple case with no context needed */ 326 jmain->pub.process_data = process_data_simple_main; 327 } 328 jmain->buffer_full = FALSE; /* Mark buffer empty */ 329 jmain->rowgroup_ctr = 0; 330 break; 331 #ifdef QUANT_2PASS_SUPPORTED 332 case JBUF_CRANK_DEST: 333 /* For last pass of 2-pass quantization, just crank the postprocessor */ 334 jmain->pub.process_data = process_data_crank_post; 335 break; 336 #endif 337 default: 338 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 339 break; 340 } 341 } 342 343 344 /* 345 * Process some data. 346 * This handles the simple case where no context is required. 347 */ 348 349 METHODDEF void 350 process_data_simple_main (j_decompress_ptr cinfo, 351 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, 352 JDIMENSION out_rows_avail) 353 { 354 // bk001204 - no use main 355 my_main_ptr jmain = (my_main_ptr) cinfo->main; 356 JDIMENSION rowgroups_avail; 357 358 /* Read input data if we haven't filled the main buffer yet */ 359 if (! jmain->buffer_full) { 360 if (! (*cinfo->coef->decompress_data) (cinfo, jmain->buffer)) 361 return; /* suspension forced, can do nothing more */ 362 jmain->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 363 } 364 365 /* There are always min_DCT_scaled_size row groups in an iMCU row. */ 366 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size; 367 /* Note: at the bottom of the image, we may pass extra garbage row groups 368 * to the postprocessor. The postprocessor has to check for bottom 369 * of image anyway (at row resolution), so no point in us doing it too. 370 */ 371 372 /* Feed the postprocessor */ 373 (*cinfo->post->post_process_data) (cinfo, jmain->buffer, 374 &jmain->rowgroup_ctr, rowgroups_avail, 375 output_buf, out_row_ctr, out_rows_avail); 376 377 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */ 378 if (jmain->rowgroup_ctr >= rowgroups_avail) { 379 jmain->buffer_full = FALSE; 380 jmain->rowgroup_ctr = 0; 381 } 382 } 383 384 385 /* 386 * Process some data. 387 * This handles the case where context rows must be provided. 388 */ 389 390 METHODDEF void 391 process_data_context_main (j_decompress_ptr cinfo, 392 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, 393 JDIMENSION out_rows_avail) 394 { 395 // bk001204 - no use main 396 my_main_ptr jmain = (my_main_ptr) cinfo->main; 397 398 /* Read input data if we haven't filled the main buffer yet */ 399 if (! jmain->buffer_full) { 400 if (! (*cinfo->coef->decompress_data) (cinfo, 401 jmain->xbuffer[jmain->whichptr])) 402 return; /* suspension forced, can do nothing more */ 403 jmain->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 404 jmain->iMCU_row_ctr++; /* count rows received */ 405 } 406 407 /* Postprocessor typically will not swallow all the input data it is handed 408 * in one call (due to filling the output buffer first). Must be prepared 409 * to exit and restart. This switch lets us keep track of how far we got. 410 * Note that each case falls through to the next on successful completion. 411 */ 412 switch (jmain->context_state) { 413 case CTX_POSTPONED_ROW: 414 /* Call postprocessor using previously set pointers for postponed row */ 415 (*cinfo->post->post_process_data) (cinfo, jmain->xbuffer[jmain->whichptr], 416 &jmain->rowgroup_ctr, jmain->rowgroups_avail, 417 output_buf, out_row_ctr, out_rows_avail); 418 if (jmain->rowgroup_ctr < jmain->rowgroups_avail) 419 return; /* Need to suspend */ 420 jmain->context_state = CTX_PREPARE_FOR_IMCU; 421 if (*out_row_ctr >= out_rows_avail) 422 return; /* Postprocessor exactly filled output buf */ 423 /*FALLTHROUGH*/ 424 case CTX_PREPARE_FOR_IMCU: 425 /* Prepare to process first M-1 row groups of this iMCU row */ 426 jmain->rowgroup_ctr = 0; 427 jmain->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1); 428 /* Check for bottom of image: if so, tweak pointers to "duplicate" 429 * the last sample row, and adjust rowgroups_avail to ignore padding rows. 430 */ 431 if (jmain->iMCU_row_ctr == cinfo->total_iMCU_rows) 432 set_bottom_pointers(cinfo); 433 jmain->context_state = CTX_PROCESS_IMCU; 434 /*FALLTHROUGH*/ 435 case CTX_PROCESS_IMCU: 436 /* Call postprocessor using previously set pointers */ 437 (*cinfo->post->post_process_data) (cinfo, jmain->xbuffer[jmain->whichptr], 438 &jmain->rowgroup_ctr, jmain->rowgroups_avail, 439 output_buf, out_row_ctr, out_rows_avail); 440 if (jmain->rowgroup_ctr < jmain->rowgroups_avail) 441 return; /* Need to suspend */ 442 /* After the first iMCU, change wraparound pointers to normal state */ 443 if (jmain->iMCU_row_ctr == 1) 444 set_wraparound_pointers(cinfo); 445 /* Prepare to load new iMCU row using other xbuffer list */ 446 jmain->whichptr ^= 1; /* 0=>1 or 1=>0 */ 447 jmain->buffer_full = FALSE; 448 /* Still need to process last row group of this iMCU row, */ 449 /* which is saved at index M+1 of the other xbuffer */ 450 jmain->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1); 451 jmain->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2); 452 jmain->context_state = CTX_POSTPONED_ROW; 453 } 454 } 455 456 457 /* 458 * Process some data. 459 * Final pass of two-pass quantization: just call the postprocessor. 460 * Source data will be the postprocessor controller's internal buffer. 461 */ 462 463 #ifdef QUANT_2PASS_SUPPORTED 464 465 METHODDEF void 466 process_data_crank_post (j_decompress_ptr cinfo, 467 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, 468 JDIMENSION out_rows_avail) 469 { 470 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL, 471 (JDIMENSION *) NULL, (JDIMENSION) 0, 472 output_buf, out_row_ctr, out_rows_avail); 473 } 474 475 #endif /* QUANT_2PASS_SUPPORTED */ 476 477 478 /* 479 * Initialize main buffer controller. 480 */ 481 482 GLOBAL void 483 jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer) 484 { 485 // bk001204 - no use main 486 my_main_ptr jmain; 487 int ci, rgroup, ngroups; 488 jpeg_component_info *compptr; 489 490 jmain = (my_main_ptr) 491 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 492 SIZEOF(my_main_controller)); 493 cinfo->main = (struct jpeg_d_main_controller *) jmain; 494 jmain->pub.start_pass = start_pass_main; 495 496 if (need_full_buffer) /* shouldn't happen */ 497 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 498 499 /* Allocate the workspace. 500 * ngroups is the number of row groups we need. 501 */ 502 if (cinfo->upsample->need_context_rows) { 503 if (cinfo->min_DCT_scaled_size < 2) /* unsupported, see comments above */ 504 ERREXIT(cinfo, JERR_NOTIMPL); 505 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */ 506 ngroups = cinfo->min_DCT_scaled_size + 2; 507 } else { 508 ngroups = cinfo->min_DCT_scaled_size; 509 } 510 511 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 512 ci++, compptr++) { 513 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 514 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 515 jmain->buffer[ci] = (*cinfo->mem->alloc_sarray) 516 ((j_common_ptr) cinfo, JPOOL_IMAGE, 517 compptr->width_in_blocks * compptr->DCT_scaled_size, 518 (JDIMENSION) (rgroup * ngroups)); 519 } 520 }