1/* 2 * jdmainct.c 3 * 4 * Copyright (C) 1994-1996, 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/* suppress the warnings about using main for the variable names */ 17#define main jpegMain 18 19#define JPEG_INTERNALS 20#include "jinclude.h" 21#include "jpeglib.h" 22 23/* 24 * In the current system design, the main buffer need never be a full-image 25 * buffer; any full-height buffers will be found inside the coefficient or 26 * postprocessing controllers. Nonetheless, the main controller is not 27 * trivial. Its responsibility is to provide context rows for upsampling/ 28 * rescaling, and doing this in an efficient fashion is a bit tricky. 29 * 30 * Postprocessor input data is counted in "row groups". A row group 31 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size) 32 * sample rows of each component. (We require DCT_scaled_size values to be 33 * chosen such that these numbers are integers. In practice DCT_scaled_size 34 * values will likely be powers of two, so we actually have the stronger 35 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.) 36 * Upsampling will typically produce max_v_samp_factor pixel rows from each 37 * row group (times any additional scale factor that the upsampler is 38 * applying). 39 * 40 * The coefficient controller will deliver data to us one iMCU row at a time; 41 * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or 42 * exactly min_DCT_scaled_size row groups. (This amount of data corresponds 43 * to one row of MCUs when the image is fully interleaved.) Note that the 44 * number of sample rows varies across components, but the number of row 45 * groups does not. Some garbage sample rows may be included in the last iMCU 46 * row at the bottom of the image. 47 * 48 * Depending on the vertical scaling algorithm used, the upsampler may need 49 * access to the sample row(s) above and below its current input row group. 50 * The upsampler is required to set need_context_rows TRUE at global selection 51 * time if so. When need_context_rows is FALSE, this controller can simply 52 * obtain one iMCU row at a time from the coefficient controller and dole it 53 * out as row groups to the postprocessor. 54 * 55 * When need_context_rows is TRUE, this controller guarantees that the buffer 56 * passed to postprocessing contains at least one row group's worth of samples 57 * above and below the row group(s) being processed. Note that the context 58 * rows "above" the first passed row group appear at negative row offsets in 59 * the passed buffer. At the top and bottom of the image, the required 60 * context rows are manufactured by duplicating the first or last real sample 61 * row; this avoids having special cases in the upsampling inner loops. 62 * 63 * The amount of context is fixed at one row group just because that's a 64 * convenient number for this controller to work with. The existing 65 * upsamplers really only need one sample row of context. An upsampler 66 * supporting arbitrary output rescaling might wish for more than one row 67 * group of context when shrinking the image; tough, we don't handle that. 68 * (This is justified by the assumption that downsizing will be handled mostly 69 * by adjusting the DCT_scaled_size values, so that the actual scale factor at 70 * the upsample step needn't be much less than one.) 71 * 72 * To provide the desired context, we have to retain the last two row groups 73 * of one iMCU row while reading in the next iMCU row. (The last row group 74 * can't be processed until we have another row group for its below-context, 75 * and so we have to save the next-to-last group too for its above-context.) 76 * We could do this most simply by copying data around in our buffer, but 77 * that'd be very slow. We can avoid copying any data by creating a rather 78 * strange pointer structure. Here's how it works. We allocate a workspace 79 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number 80 * of row groups per iMCU row). We create two sets of redundant pointers to 81 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized 82 * pointer lists look like this: 83 * M+1 M-1 84 * master pointer --> 0 master pointer --> 0 85 * 1 1 86 * ... ... 87 * M-3 M-3 88 * M-2 M 89 * M-1 M+1 90 * M M-2 91 * M+1 M-1 92 * 0 0 93 * We read alternate iMCU rows using each master pointer; thus the last two 94 * row groups of the previous iMCU row remain un-overwritten in the workspace. 95 * The pointer lists are set up so that the required context rows appear to 96 * be adjacent to the proper places when we pass the pointer lists to the 97 * upsampler. 98 * 99 * The above pictures describe the normal state of the pointer lists. 100 * At top and bottom of the image, we diddle the pointer lists to duplicate 101 * the first or last sample row as necessary (this is cheaper than copying 102 * sample rows around). 103 * 104 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that 105 * situation each iMCU row provides only one row group so the buffering logic 106 * must be different (eg, we must read two iMCU rows before we can emit the 107 * first row group). For now, we simply do not support providing context 108 * rows when min_DCT_scaled_size is 1. That combination seems unlikely to 109 * be worth providing --- if someone wants a 1/8th-size preview, they probably 110 * want it quick and dirty, so a context-free upsampler is sufficient. 111 */ 112 113 114/* Private buffer controller object */ 115 116typedef struct { 117 struct jpeg_d_main_controller pub; /* public fields */ 118 119 /* Pointer to allocated workspace (M or M+2 row groups). */ 120 JSAMPARRAY buffer[MAX_COMPONENTS]; 121 122 wxjpeg_boolean buffer_full; /* Have we gotten an iMCU row from decoder? */ 123 JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */ 124 125 /* Remaining fields are only used in the context case. */ 126 127 /* These are the master pointers to the funny-order pointer lists. */ 128 JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */ 129 130 int whichptr; /* indicates which pointer set is now in use */ 131 int context_state; /* process_data state machine status */ 132 JDIMENSION rowgroups_avail; /* row groups available to postprocessor */ 133 JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */ 134} my_main_controller; 135 136typedef my_main_controller * my_main_ptr; 137 138/* context_state values: */ 139#define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */ 140#define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */ 141#define CTX_POSTPONED_ROW 2 /* feeding postponed row group */ 142 143 144#if defined(__VISAGECPP__) 145/* Visual Age fixups for multiple declarations */ 146# define start_pass_main start_pass_main2 /* already in jcmaint.c */ 147# define process_data_simple_main process_data_simple_main2 /* already in jcmaint.c */ 148#endif 149 150/* Forward declarations */ 151METHODDEF(void) process_data_simple_main 152 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf, 153 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)); 154METHODDEF(void) process_data_context_main 155 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf, 156 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)); 157#ifdef QUANT_2PASS_SUPPORTED 158METHODDEF(void) process_data_crank_post 159 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf, 160 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)); 161#endif 162 163 164LOCAL(void) 165alloc_funny_pointers (j_decompress_ptr cinfo) 166/* Allocate space for the funny pointer lists. 167 * This is done only once, not once per pass. 168 */ 169{ 170 my_main_ptr main = (my_main_ptr) cinfo->main; 171 int ci, rgroup; 172 int M = cinfo->min_DCT_scaled_size; 173 jpeg_component_info *compptr; 174 JSAMPARRAY xbuf; 175 176 /* Get top-level space for component array pointers. 177 * We alloc both arrays with one call to save a few cycles. 178 */ 179 main->xbuffer[0] = (JSAMPIMAGE) 180 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 181 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY)); 182 main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components; 183 184 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 185 ci++, compptr++) { 186 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 187 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 188 /* Get space for pointer lists --- M+4 row groups in each list. 189 * We alloc both pointer lists with one call to save a few cycles. 190 */ 191 xbuf = (JSAMPARRAY) 192 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 193 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW)); 194 xbuf += rgroup; /* want one row group at negative offsets */ 195 main->xbuffer[0][ci] = xbuf; 196 xbuf += rgroup * (M + 4); 197 main->xbuffer[1][ci] = xbuf; 198 } 199} 200 201 202LOCAL(void) 203make_funny_pointers (j_decompress_ptr cinfo) 204/* Create the funny pointer lists discussed in the comments above. 205 * The actual workspace is already allocated (in main->buffer), 206 * and the space for the pointer lists is allocated too. 207 * This routine just fills in the curiously ordered lists. 208 * This will be repeated at the beginning of each pass. 209 */ 210{ 211 my_main_ptr main = (my_main_ptr) cinfo->main; 212 int ci, i, rgroup; 213 int M = cinfo->min_DCT_scaled_size; 214 jpeg_component_info *compptr; 215 JSAMPARRAY buf, xbuf0, xbuf1; 216 217 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 218 ci++, compptr++) { 219 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 220 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 221 xbuf0 = main->xbuffer[0][ci]; 222 xbuf1 = main->xbuffer[1][ci]; 223 /* First copy the workspace pointers as-is */ 224 buf = main->buffer[ci]; 225 for (i = 0; i < rgroup * (M + 2); i++) { 226 xbuf0[i] = xbuf1[i] = buf[i]; 227 } 228 /* In the second list, put the last four row groups in swapped order */ 229 for (i = 0; i < rgroup * 2; i++) { 230 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i]; 231 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i]; 232 } 233 /* The wraparound pointers at top and bottom will be filled later 234 * (see set_wraparound_pointers, below). Initially we want the "above" 235 * pointers to duplicate the first actual data line. This only needs 236 * to happen in xbuffer[0]. 237 */ 238 for (i = 0; i < rgroup; i++) { 239 xbuf0[i - rgroup] = xbuf0[0]; 240 } 241 } 242} 243 244 245LOCAL(void) 246set_wraparound_pointers (j_decompress_ptr cinfo) 247/* Set up the "wraparound" pointers at top and bottom of the pointer lists. 248 * This changes the pointer list state from top-of-image to the normal state. 249 */ 250{ 251 my_main_ptr main = (my_main_ptr) cinfo->main; 252 int ci, i, rgroup; 253 int M = cinfo->min_DCT_scaled_size; 254 jpeg_component_info *compptr; 255 JSAMPARRAY xbuf0, xbuf1; 256 257 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 258 ci++, compptr++) { 259 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 260 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 261 xbuf0 = main->xbuffer[0][ci]; 262 xbuf1 = main->xbuffer[1][ci]; 263 for (i = 0; i < rgroup; i++) { 264 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i]; 265 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i]; 266 xbuf0[rgroup*(M+2) + i] = xbuf0[i]; 267 xbuf1[rgroup*(M+2) + i] = xbuf1[i]; 268 } 269 } 270} 271 272 273LOCAL(void) 274set_bottom_pointers (j_decompress_ptr cinfo) 275/* Change the pointer lists to duplicate the last sample row at the bottom 276 * of the image. whichptr indicates which xbuffer holds the final iMCU row. 277 * Also sets rowgroups_avail to indicate number of nondummy row groups in row. 278 */ 279{ 280 my_main_ptr main = (my_main_ptr) cinfo->main; 281 int ci, i, rgroup, iMCUheight, rows_left; 282 jpeg_component_info *compptr; 283 JSAMPARRAY xbuf; 284 285 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 286 ci++, compptr++) { 287 /* Count sample rows in one iMCU row and in one row group */ 288 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size; 289 rgroup = iMCUheight / cinfo->min_DCT_scaled_size; 290 /* Count nondummy sample rows remaining for this component */ 291 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight); 292 if (rows_left == 0) rows_left = iMCUheight; 293 /* Count nondummy row groups. Should get same answer for each component, 294 * so we need only do it once. 295 */ 296 if (ci == 0) { 297 main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1); 298 } 299 /* Duplicate the last real sample row rgroup*2 times; this pads out the 300 * last partial rowgroup and ensures at least one full rowgroup of context. 301 */ 302 xbuf = main->xbuffer[main->whichptr][ci]; 303 for (i = 0; i < rgroup * 2; i++) { 304 xbuf[rows_left + i] = xbuf[rows_left-1]; 305 } 306 } 307} 308 309 310/* 311 * Initialize for a processing pass. 312 */ 313 314METHODDEF(void) 315start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode) 316{ 317 my_main_ptr main = (my_main_ptr) cinfo->main; 318 319 switch (pass_mode) { 320 case JBUF_PASS_THRU: 321 if (cinfo->upsample->need_context_rows) { 322 main->pub.process_data = process_data_context_main; 323 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */ 324 main->whichptr = 0; /* Read first iMCU row into xbuffer[0] */ 325 main->context_state = CTX_PREPARE_FOR_IMCU; 326 main->iMCU_row_ctr = 0; 327 } else { 328 /* Simple case with no context needed */ 329 main->pub.process_data = process_data_simple_main; 330 } 331 main->buffer_full = FALSE; /* Mark buffer empty */ 332 main->rowgroup_ctr = 0; 333 break; 334#ifdef QUANT_2PASS_SUPPORTED 335 case JBUF_CRANK_DEST: 336 /* For last pass of 2-pass quantization, just crank the postprocessor */ 337 main->pub.process_data = process_data_crank_post; 338 break; 339#endif 340 default: 341 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 342 break; 343 } 344} 345 346 347/* 348 * Process some data. 349 * This handles the simple case where no context is required. 350 */ 351 352METHODDEF(void) 353process_data_simple_main (j_decompress_ptr cinfo, 354 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, 355 JDIMENSION out_rows_avail) 356{ 357 my_main_ptr main = (my_main_ptr) cinfo->main; 358 JDIMENSION rowgroups_avail; 359 360 /* Read input data if we haven't filled the main buffer yet */ 361 if (! main->buffer_full) { 362 if (! (*cinfo->coef->decompress_data) (cinfo, main->buffer)) 363 return; /* suspension forced, can do nothing more */ 364 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 365 } 366 367 /* There are always min_DCT_scaled_size row groups in an iMCU row. */ 368 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size; 369 /* Note: at the bottom of the image, we may pass extra garbage row groups 370 * to the postprocessor. The postprocessor has to check for bottom 371 * of image anyway (at row resolution), so no point in us doing it too. 372 */ 373 374 /* Feed the postprocessor */ 375 (*cinfo->post->post_process_data) (cinfo, main->buffer, 376 &main->rowgroup_ctr, rowgroups_avail, 377 output_buf, out_row_ctr, out_rows_avail); 378 379 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */ 380 if (main->rowgroup_ctr >= rowgroups_avail) { 381 main->buffer_full = FALSE; 382 main->rowgroup_ctr = 0; 383 } 384} 385 386 387/* 388 * Process some data. 389 * This handles the case where context rows must be provided. 390 */ 391 392METHODDEF(void) 393process_data_context_main (j_decompress_ptr cinfo, 394 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, 395 JDIMENSION out_rows_avail) 396{ 397 my_main_ptr main = (my_main_ptr) cinfo->main; 398 399 /* Read input data if we haven't filled the main buffer yet */ 400 if (! main->buffer_full) { 401 if (! (*cinfo->coef->decompress_data) (cinfo, 402 main->xbuffer[main->whichptr])) 403 return; /* suspension forced, can do nothing more */ 404 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 405 main->iMCU_row_ctr++; /* count rows received */ 406 } 407 408 /* Postprocessor typically will not swallow all the input data it is handed 409 * in one call (due to filling the output buffer first). Must be prepared 410 * to exit and restart. This switch lets us keep track of how far we got. 411 * Note that each case falls through to the next on successful completion. 412 */ 413 switch (main->context_state) { 414 case CTX_POSTPONED_ROW: 415 /* Call postprocessor using previously set pointers for postponed row */ 416 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr], 417 &main->rowgroup_ctr, main->rowgroups_avail, 418 output_buf, out_row_ctr, out_rows_avail); 419 if (main->rowgroup_ctr < main->rowgroups_avail) 420 return; /* Need to suspend */ 421 main->context_state = CTX_PREPARE_FOR_IMCU; 422 if (*out_row_ctr >= out_rows_avail) 423 return; /* Postprocessor exactly filled output buf */ 424 /*FALLTHROUGH*/ 425 case CTX_PREPARE_FOR_IMCU: 426 /* Prepare to process first M-1 row groups of this iMCU row */ 427 main->rowgroup_ctr = 0; 428 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1); 429 /* Check for bottom of image: if so, tweak pointers to "duplicate" 430 * the last sample row, and adjust rowgroups_avail to ignore padding rows. 431 */ 432 if (main->iMCU_row_ctr == cinfo->total_iMCU_rows) 433 set_bottom_pointers(cinfo); 434 main->context_state = CTX_PROCESS_IMCU; 435 /*FALLTHROUGH*/ 436 case CTX_PROCESS_IMCU: 437 /* Call postprocessor using previously set pointers */ 438 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr], 439 &main->rowgroup_ctr, main->rowgroups_avail, 440 output_buf, out_row_ctr, out_rows_avail); 441 if (main->rowgroup_ctr < main->rowgroups_avail) 442 return; /* Need to suspend */ 443 /* After the first iMCU, change wraparound pointers to normal state */ 444 if (main->iMCU_row_ctr == 1) 445 set_wraparound_pointers(cinfo); 446 /* Prepare to load new iMCU row using other xbuffer list */ 447 main->whichptr ^= 1; /* 0=>1 or 1=>0 */ 448 main->buffer_full = FALSE; 449 /* Still need to process last row group of this iMCU row, */ 450 /* which is saved at index M+1 of the other xbuffer */ 451 main->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1); 452 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2); 453 main->context_state = CTX_POSTPONED_ROW; 454 } 455} 456 457 458/* 459 * Process some data. 460 * Final pass of two-pass quantization: just call the postprocessor. 461 * Source data will be the postprocessor controller's internal buffer. 462 */ 463 464#ifdef QUANT_2PASS_SUPPORTED 465 466METHODDEF(void) 467process_data_crank_post (j_decompress_ptr cinfo, 468 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, 469 JDIMENSION out_rows_avail) 470{ 471 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL, 472 (JDIMENSION *) NULL, (JDIMENSION) 0, 473 output_buf, out_row_ctr, out_rows_avail); 474} 475 476#endif /* QUANT_2PASS_SUPPORTED */ 477 478 479/* 480 * Initialize main buffer controller. 481 */ 482 483GLOBAL(void) 484jinit_d_main_controller (j_decompress_ptr cinfo, wxjpeg_boolean need_full_buffer) 485{ 486 my_main_ptr main; 487 int ci, rgroup, ngroups; 488 jpeg_component_info *compptr; 489 490 main = (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 *) main; 494 main->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 main->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} 521 522#if defined(__VISAGECPP__) 523# ifdef start_pass_main2 524# undef start_pass_main2 525# endif 526# ifdef process_data_simple_main2 527# undef process_data_simple_main2 528# endif 529#endif 530