jdmainct.c (20366B)
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 #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 my_main_ptr main = (my_main_ptr) cinfo->main; 163 int ci, rgroup; 164 int M = cinfo->min_DCT_scaled_size; 165 jpeg_component_info *compptr; 166 JSAMPARRAY xbuf; 167 168 /* Get top-level space for component array pointers. 169 * We alloc both arrays with one call to save a few cycles. 170 */ 171 main->xbuffer[0] = (JSAMPIMAGE) 172 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 173 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY)); 174 main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components; 175 176 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 177 ci++, compptr++) { 178 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 179 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 180 /* Get space for pointer lists --- M+4 row groups in each list. 181 * We alloc both pointer lists with one call to save a few cycles. 182 */ 183 xbuf = (JSAMPARRAY) 184 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 185 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW)); 186 xbuf += rgroup; /* want one row group at negative offsets */ 187 main->xbuffer[0][ci] = xbuf; 188 xbuf += rgroup * (M + 4); 189 main->xbuffer[1][ci] = xbuf; 190 } 191 } 192 193 194 LOCAL(void) 195 make_funny_pointers (j_decompress_ptr cinfo) 196 /* Create the funny pointer lists discussed in the comments above. 197 * The actual workspace is already allocated (in main->buffer), 198 * and the space for the pointer lists is allocated too. 199 * This routine just fills in the curiously ordered lists. 200 * This will be repeated at the beginning of each pass. 201 */ 202 { 203 my_main_ptr main = (my_main_ptr) cinfo->main; 204 int ci, i, rgroup; 205 int M = cinfo->min_DCT_scaled_size; 206 jpeg_component_info *compptr; 207 JSAMPARRAY buf, xbuf0, xbuf1; 208 209 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 210 ci++, compptr++) { 211 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 212 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 213 xbuf0 = main->xbuffer[0][ci]; 214 xbuf1 = main->xbuffer[1][ci]; 215 /* First copy the workspace pointers as-is */ 216 buf = main->buffer[ci]; 217 for (i = 0; i < rgroup * (M + 2); i++) { 218 xbuf0[i] = xbuf1[i] = buf[i]; 219 } 220 /* In the second list, put the last four row groups in swapped order */ 221 for (i = 0; i < rgroup * 2; i++) { 222 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i]; 223 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i]; 224 } 225 /* The wraparound pointers at top and bottom will be filled later 226 * (see set_wraparound_pointers, below). Initially we want the "above" 227 * pointers to duplicate the first actual data line. This only needs 228 * to happen in xbuffer[0]. 229 */ 230 for (i = 0; i < rgroup; i++) { 231 xbuf0[i - rgroup] = xbuf0[0]; 232 } 233 } 234 } 235 236 237 LOCAL(void) 238 set_wraparound_pointers (j_decompress_ptr cinfo) 239 /* Set up the "wraparound" pointers at top and bottom of the pointer lists. 240 * This changes the pointer list state from top-of-image to the normal state. 241 */ 242 { 243 my_main_ptr main = (my_main_ptr) cinfo->main; 244 int ci, i, rgroup; 245 int M = cinfo->min_DCT_scaled_size; 246 jpeg_component_info *compptr; 247 JSAMPARRAY xbuf0, xbuf1; 248 249 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 250 ci++, compptr++) { 251 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 252 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 253 xbuf0 = main->xbuffer[0][ci]; 254 xbuf1 = main->xbuffer[1][ci]; 255 for (i = 0; i < rgroup; i++) { 256 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i]; 257 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i]; 258 xbuf0[rgroup*(M+2) + i] = xbuf0[i]; 259 xbuf1[rgroup*(M+2) + i] = xbuf1[i]; 260 } 261 } 262 } 263 264 265 LOCAL(void) 266 set_bottom_pointers (j_decompress_ptr cinfo) 267 /* Change the pointer lists to duplicate the last sample row at the bottom 268 * of the image. whichptr indicates which xbuffer holds the final iMCU row. 269 * Also sets rowgroups_avail to indicate number of nondummy row groups in row. 270 */ 271 { 272 my_main_ptr main = (my_main_ptr) cinfo->main; 273 int ci, i, rgroup, iMCUheight, rows_left; 274 jpeg_component_info *compptr; 275 JSAMPARRAY xbuf; 276 277 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 278 ci++, compptr++) { 279 /* Count sample rows in one iMCU row and in one row group */ 280 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size; 281 rgroup = iMCUheight / cinfo->min_DCT_scaled_size; 282 /* Count nondummy sample rows remaining for this component */ 283 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight); 284 if (rows_left == 0) rows_left = iMCUheight; 285 /* Count nondummy row groups. Should get same answer for each component, 286 * so we need only do it once. 287 */ 288 if (ci == 0) { 289 main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1); 290 } 291 /* Duplicate the last real sample row rgroup*2 times; this pads out the 292 * last partial rowgroup and ensures at least one full rowgroup of context. 293 */ 294 xbuf = main->xbuffer[main->whichptr][ci]; 295 for (i = 0; i < rgroup * 2; i++) { 296 xbuf[rows_left + i] = xbuf[rows_left-1]; 297 } 298 } 299 } 300 301 302 /* 303 * Initialize for a processing pass. 304 */ 305 306 METHODDEF(void) 307 start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode) 308 { 309 my_main_ptr main = (my_main_ptr) cinfo->main; 310 311 switch (pass_mode) { 312 case JBUF_PASS_THRU: 313 if (cinfo->upsample->need_context_rows) { 314 main->pub.process_data = process_data_context_main; 315 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */ 316 main->whichptr = 0; /* Read first iMCU row into xbuffer[0] */ 317 main->context_state = CTX_PREPARE_FOR_IMCU; 318 main->iMCU_row_ctr = 0; 319 } else { 320 /* Simple case with no context needed */ 321 main->pub.process_data = process_data_simple_main; 322 } 323 main->buffer_full = FALSE; /* Mark buffer empty */ 324 main->rowgroup_ctr = 0; 325 break; 326 #ifdef QUANT_2PASS_SUPPORTED 327 case JBUF_CRANK_DEST: 328 /* For last pass of 2-pass quantization, just crank the postprocessor */ 329 main->pub.process_data = process_data_crank_post; 330 break; 331 #endif 332 default: 333 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 334 break; 335 } 336 } 337 338 339 /* 340 * Process some data. 341 * This handles the simple case where no context is required. 342 */ 343 344 METHODDEF(void) 345 process_data_simple_main (j_decompress_ptr cinfo, 346 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, 347 JDIMENSION out_rows_avail) 348 { 349 my_main_ptr main = (my_main_ptr) cinfo->main; 350 JDIMENSION rowgroups_avail; 351 352 /* Read input data if we haven't filled the main buffer yet */ 353 if (! main->buffer_full) { 354 if (! (*cinfo->coef->decompress_data) (cinfo, main->buffer)) 355 return; /* suspension forced, can do nothing more */ 356 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 357 } 358 359 /* There are always min_DCT_scaled_size row groups in an iMCU row. */ 360 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size; 361 /* Note: at the bottom of the image, we may pass extra garbage row groups 362 * to the postprocessor. The postprocessor has to check for bottom 363 * of image anyway (at row resolution), so no point in us doing it too. 364 */ 365 366 /* Feed the postprocessor */ 367 (*cinfo->post->post_process_data) (cinfo, main->buffer, 368 &main->rowgroup_ctr, rowgroups_avail, 369 output_buf, out_row_ctr, out_rows_avail); 370 371 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */ 372 if (main->rowgroup_ctr >= rowgroups_avail) { 373 main->buffer_full = FALSE; 374 main->rowgroup_ctr = 0; 375 } 376 } 377 378 379 /* 380 * Process some data. 381 * This handles the case where context rows must be provided. 382 */ 383 384 METHODDEF(void) 385 process_data_context_main (j_decompress_ptr cinfo, 386 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, 387 JDIMENSION out_rows_avail) 388 { 389 my_main_ptr main = (my_main_ptr) cinfo->main; 390 391 /* Read input data if we haven't filled the main buffer yet */ 392 if (! main->buffer_full) { 393 if (! (*cinfo->coef->decompress_data) (cinfo, 394 main->xbuffer[main->whichptr])) 395 return; /* suspension forced, can do nothing more */ 396 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 397 main->iMCU_row_ctr++; /* count rows received */ 398 } 399 400 /* Postprocessor typically will not swallow all the input data it is handed 401 * in one call (due to filling the output buffer first). Must be prepared 402 * to exit and restart. This switch lets us keep track of how far we got. 403 * Note that each case falls through to the next on successful completion. 404 */ 405 switch (main->context_state) { 406 case CTX_POSTPONED_ROW: 407 /* Call postprocessor using previously set pointers for postponed row */ 408 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr], 409 &main->rowgroup_ctr, main->rowgroups_avail, 410 output_buf, out_row_ctr, out_rows_avail); 411 if (main->rowgroup_ctr < main->rowgroups_avail) 412 return; /* Need to suspend */ 413 main->context_state = CTX_PREPARE_FOR_IMCU; 414 if (*out_row_ctr >= out_rows_avail) 415 return; /* Postprocessor exactly filled output buf */ 416 /*FALLTHROUGH*/ 417 case CTX_PREPARE_FOR_IMCU: 418 /* Prepare to process first M-1 row groups of this iMCU row */ 419 main->rowgroup_ctr = 0; 420 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1); 421 /* Check for bottom of image: if so, tweak pointers to "duplicate" 422 * the last sample row, and adjust rowgroups_avail to ignore padding rows. 423 */ 424 if (main->iMCU_row_ctr == cinfo->total_iMCU_rows) 425 set_bottom_pointers(cinfo); 426 main->context_state = CTX_PROCESS_IMCU; 427 /*FALLTHROUGH*/ 428 case CTX_PROCESS_IMCU: 429 /* Call postprocessor using previously set pointers */ 430 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr], 431 &main->rowgroup_ctr, main->rowgroups_avail, 432 output_buf, out_row_ctr, out_rows_avail); 433 if (main->rowgroup_ctr < main->rowgroups_avail) 434 return; /* Need to suspend */ 435 /* After the first iMCU, change wraparound pointers to normal state */ 436 if (main->iMCU_row_ctr == 1) 437 set_wraparound_pointers(cinfo); 438 /* Prepare to load new iMCU row using other xbuffer list */ 439 main->whichptr ^= 1; /* 0=>1 or 1=>0 */ 440 main->buffer_full = FALSE; 441 /* Still need to process last row group of this iMCU row, */ 442 /* which is saved at index M+1 of the other xbuffer */ 443 main->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1); 444 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2); 445 main->context_state = CTX_POSTPONED_ROW; 446 } 447 } 448 449 450 /* 451 * Process some data. 452 * Final pass of two-pass quantization: just call the postprocessor. 453 * Source data will be the postprocessor controller's internal buffer. 454 */ 455 456 #ifdef QUANT_2PASS_SUPPORTED 457 458 METHODDEF(void) 459 process_data_crank_post (j_decompress_ptr cinfo, 460 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr, 461 JDIMENSION out_rows_avail) 462 { 463 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL, 464 (JDIMENSION *) NULL, (JDIMENSION) 0, 465 output_buf, out_row_ctr, out_rows_avail); 466 } 467 468 #endif /* QUANT_2PASS_SUPPORTED */ 469 470 471 /* 472 * Initialize main buffer controller. 473 */ 474 475 GLOBAL(void) 476 jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer) 477 { 478 my_main_ptr main; 479 int ci, rgroup, ngroups; 480 jpeg_component_info *compptr; 481 482 main = (my_main_ptr) 483 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 484 SIZEOF(my_main_controller)); 485 cinfo->main = (struct jpeg_d_main_controller *) main; 486 main->pub.start_pass = start_pass_main; 487 488 if (need_full_buffer) /* shouldn't happen */ 489 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 490 491 /* Allocate the workspace. 492 * ngroups is the number of row groups we need. 493 */ 494 if (cinfo->upsample->need_context_rows) { 495 if (cinfo->min_DCT_scaled_size < 2) /* unsupported, see comments above */ 496 ERREXIT(cinfo, JERR_NOTIMPL); 497 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */ 498 ngroups = cinfo->min_DCT_scaled_size + 2; 499 } else { 500 ngroups = cinfo->min_DCT_scaled_size; 501 } 502 503 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 504 ci++, compptr++) { 505 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) / 506 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 507 main->buffer[ci] = (*cinfo->mem->alloc_sarray) 508 ((j_common_ptr) cinfo, JPOOL_IMAGE, 509 compptr->width_in_blocks * compptr->DCT_scaled_size, 510 (JDIMENSION) (rgroup * ngroups)); 511 } 512 }