jdmainct.c (20170B)
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, 2022, 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 22 23 #if BITS_IN_JSAMPLE != 16 || defined(D_LOSSLESS_SUPPORTED) 24 25 /* 26 * In the current system design, the main buffer need never be a full-image 27 * buffer; any full-height buffers will be found inside the coefficient, 28 * difference, or postprocessing controllers. Nonetheless, the main controller 29 * is not trivial. Its responsibility is to provide context rows for 30 * upsampling/rescaling, and doing this in an efficient fashion is a bit 31 * tricky. 32 * 33 * Postprocessor input data is counted in "row groups". A row group 34 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size) 35 * sample rows of each component. (We require DCT_scaled_size values to be 36 * chosen such that these numbers are integers. In practice DCT_scaled_size 37 * values will likely be powers of two, so we actually have the stronger 38 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.) 39 * Upsampling will typically produce max_v_samp_factor pixel rows from each 40 * row group (times any additional scale factor that the upsampler is 41 * applying). 42 * 43 * The coefficient or difference controller will deliver data to us one iMCU 44 * row at a time; each iMCU row contains v_samp_factor * DCT_scaled_size sample 45 * rows, or exactly min_DCT_scaled_size row groups. (This amount of data 46 * corresponds to one row of MCUs when the image is fully interleaved.) Note 47 * that the number of sample rows varies across components, but the number of 48 * row groups does not. Some garbage sample rows may be included in the last 49 * iMCU row at the bottom of the image. 50 * 51 * Depending on the vertical scaling algorithm used, the upsampler may need 52 * access to the sample row(s) above and below its current input row group. 53 * The upsampler is required to set need_context_rows TRUE at global selection 54 * time if so. When need_context_rows is FALSE, this controller can simply 55 * obtain one iMCU row at a time from the coefficient or difference controller 56 * and dole it out as row groups to the postprocessor. 57 * 58 * When need_context_rows is TRUE, this controller guarantees that the buffer 59 * passed to postprocessing contains at least one row group's worth of samples 60 * above and below the row group(s) being processed. Note that the context 61 * rows "above" the first passed row group appear at negative row offsets in 62 * the passed buffer. At the top and bottom of the image, the required 63 * context rows are manufactured by duplicating the first or last real sample 64 * row; this avoids having special cases in the upsampling inner loops. 65 * 66 * The amount of context is fixed at one row group just because that's a 67 * convenient number for this controller to work with. The existing 68 * upsamplers really only need one sample row of context. An upsampler 69 * supporting arbitrary output rescaling might wish for more than one row 70 * group of context when shrinking the image; tough, we don't handle that. 71 * (This is justified by the assumption that downsizing will be handled mostly 72 * by adjusting the DCT_scaled_size values, so that the actual scale factor at 73 * the upsample step needn't be much less than one.) 74 * 75 * To provide the desired context, we have to retain the last two row groups 76 * of one iMCU row while reading in the next iMCU row. (The last row group 77 * can't be processed until we have another row group for its below-context, 78 * and so we have to save the next-to-last group too for its above-context.) 79 * We could do this most simply by copying data around in our buffer, but 80 * that'd be very slow. We can avoid copying any data by creating a rather 81 * strange pointer structure. Here's how it works. We allocate a workspace 82 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number 83 * of row groups per iMCU row). We create two sets of redundant pointers to 84 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized 85 * pointer lists look like this: 86 * M+1 M-1 87 * master pointer --> 0 master pointer --> 0 88 * 1 1 89 * ... ... 90 * M-3 M-3 91 * M-2 M 92 * M-1 M+1 93 * M M-2 94 * M+1 M-1 95 * 0 0 96 * We read alternate iMCU rows using each master pointer; thus the last two 97 * row groups of the previous iMCU row remain un-overwritten in the workspace. 98 * The pointer lists are set up so that the required context rows appear to 99 * be adjacent to the proper places when we pass the pointer lists to the 100 * upsampler. 101 * 102 * The above pictures describe the normal state of the pointer lists. 103 * At top and bottom of the image, we diddle the pointer lists to duplicate 104 * the first or last sample row as necessary (this is cheaper than copying 105 * sample rows around). 106 * 107 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that 108 * situation each iMCU row provides only one row group so the buffering logic 109 * must be different (eg, we must read two iMCU rows before we can emit the 110 * first row group). For now, we simply do not support providing context 111 * rows when min_DCT_scaled_size is 1. That combination seems unlikely to 112 * be worth providing --- if someone wants a 1/8th-size preview, they probably 113 * want it quick and dirty, so a context-free upsampler is sufficient. 114 */ 115 116 117 /* Forward declarations */ 118 METHODDEF(void) process_data_simple_main(j_decompress_ptr cinfo, 119 _JSAMPARRAY output_buf, 120 JDIMENSION *out_row_ctr, 121 JDIMENSION out_rows_avail); 122 METHODDEF(void) process_data_context_main(j_decompress_ptr cinfo, 123 _JSAMPARRAY output_buf, 124 JDIMENSION *out_row_ctr, 125 JDIMENSION out_rows_avail); 126 #ifdef QUANT_2PASS_SUPPORTED 127 METHODDEF(void) process_data_crank_post(j_decompress_ptr cinfo, 128 _JSAMPARRAY output_buf, 129 JDIMENSION *out_row_ctr, 130 JDIMENSION out_rows_avail); 131 #endif 132 133 134 LOCAL(void) 135 alloc_funny_pointers(j_decompress_ptr cinfo) 136 /* Allocate space for the funny pointer lists. 137 * This is done only once, not once per pass. 138 */ 139 { 140 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 141 int ci, rgroup; 142 int M = cinfo->_min_DCT_scaled_size; 143 jpeg_component_info *compptr; 144 _JSAMPARRAY xbuf; 145 146 /* Get top-level space for component array pointers. 147 * We alloc both arrays with one call to save a few cycles. 148 */ 149 main_ptr->xbuffer[0] = (_JSAMPIMAGE) 150 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 151 cinfo->num_components * 2 * 152 sizeof(_JSAMPARRAY)); 153 main_ptr->xbuffer[1] = main_ptr->xbuffer[0] + cinfo->num_components; 154 155 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 156 ci++, compptr++) { 157 rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) / 158 cinfo->_min_DCT_scaled_size; /* height of a row group of component */ 159 /* Get space for pointer lists --- M+4 row groups in each list. 160 * We alloc both pointer lists with one call to save a few cycles. 161 */ 162 xbuf = (_JSAMPARRAY) 163 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 164 2 * (rgroup * (M + 4)) * sizeof(_JSAMPROW)); 165 xbuf += rgroup; /* want one row group at negative offsets */ 166 main_ptr->xbuffer[0][ci] = xbuf; 167 xbuf += rgroup * (M + 4); 168 main_ptr->xbuffer[1][ci] = xbuf; 169 } 170 } 171 172 173 LOCAL(void) 174 make_funny_pointers(j_decompress_ptr cinfo) 175 /* Create the funny pointer lists discussed in the comments above. 176 * The actual workspace is already allocated (in main_ptr->buffer), 177 * and the space for the pointer lists is allocated too. 178 * This routine just fills in the curiously ordered lists. 179 * This will be repeated at the beginning of each pass. 180 */ 181 { 182 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 183 int ci, i, rgroup; 184 int M = cinfo->_min_DCT_scaled_size; 185 jpeg_component_info *compptr; 186 _JSAMPARRAY buf, xbuf0, xbuf1; 187 188 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 189 ci++, compptr++) { 190 rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) / 191 cinfo->_min_DCT_scaled_size; /* height of a row group of component */ 192 xbuf0 = main_ptr->xbuffer[0][ci]; 193 xbuf1 = main_ptr->xbuffer[1][ci]; 194 /* First copy the workspace pointers as-is */ 195 buf = main_ptr->buffer[ci]; 196 for (i = 0; i < rgroup * (M + 2); i++) { 197 xbuf0[i] = xbuf1[i] = buf[i]; 198 } 199 /* In the second list, put the last four row groups in swapped order */ 200 for (i = 0; i < rgroup * 2; i++) { 201 xbuf1[rgroup * (M - 2) + i] = buf[rgroup * M + i]; 202 xbuf1[rgroup * M + i] = buf[rgroup * (M - 2) + i]; 203 } 204 /* The wraparound pointers at top and bottom will be filled later 205 * (see set_wraparound_pointers, below). Initially we want the "above" 206 * pointers to duplicate the first actual data line. This only needs 207 * to happen in xbuffer[0]. 208 */ 209 for (i = 0; i < rgroup; i++) { 210 xbuf0[i - rgroup] = xbuf0[0]; 211 } 212 } 213 } 214 215 216 LOCAL(void) 217 set_bottom_pointers(j_decompress_ptr cinfo) 218 /* Change the pointer lists to duplicate the last sample row at the bottom 219 * of the image. whichptr indicates which xbuffer holds the final iMCU row. 220 * Also sets rowgroups_avail to indicate number of nondummy row groups in row. 221 */ 222 { 223 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 224 int ci, i, rgroup, iMCUheight, rows_left; 225 jpeg_component_info *compptr; 226 _JSAMPARRAY xbuf; 227 228 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 229 ci++, compptr++) { 230 /* Count sample rows in one iMCU row and in one row group */ 231 iMCUheight = compptr->v_samp_factor * compptr->_DCT_scaled_size; 232 rgroup = iMCUheight / cinfo->_min_DCT_scaled_size; 233 /* Count nondummy sample rows remaining for this component */ 234 rows_left = (int)(compptr->downsampled_height % (JDIMENSION)iMCUheight); 235 if (rows_left == 0) rows_left = iMCUheight; 236 /* Count nondummy row groups. Should get same answer for each component, 237 * so we need only do it once. 238 */ 239 if (ci == 0) { 240 main_ptr->rowgroups_avail = (JDIMENSION)((rows_left - 1) / rgroup + 1); 241 } 242 /* Duplicate the last real sample row rgroup*2 times; this pads out the 243 * last partial rowgroup and ensures at least one full rowgroup of context. 244 */ 245 xbuf = main_ptr->xbuffer[main_ptr->whichptr][ci]; 246 for (i = 0; i < rgroup * 2; i++) { 247 xbuf[rows_left + i] = xbuf[rows_left - 1]; 248 } 249 } 250 } 251 252 253 /* 254 * Initialize for a processing pass. 255 */ 256 257 METHODDEF(void) 258 start_pass_main(j_decompress_ptr cinfo, J_BUF_MODE pass_mode) 259 { 260 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 261 262 switch (pass_mode) { 263 case JBUF_PASS_THRU: 264 if (cinfo->upsample->need_context_rows) { 265 main_ptr->pub._process_data = process_data_context_main; 266 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */ 267 main_ptr->whichptr = 0; /* Read first iMCU row into xbuffer[0] */ 268 main_ptr->context_state = CTX_PREPARE_FOR_IMCU; 269 main_ptr->iMCU_row_ctr = 0; 270 } else { 271 /* Simple case with no context needed */ 272 main_ptr->pub._process_data = process_data_simple_main; 273 } 274 main_ptr->buffer_full = FALSE; /* Mark buffer empty */ 275 main_ptr->rowgroup_ctr = 0; 276 break; 277 #ifdef QUANT_2PASS_SUPPORTED 278 case JBUF_CRANK_DEST: 279 /* For last pass of 2-pass quantization, just crank the postprocessor */ 280 main_ptr->pub._process_data = process_data_crank_post; 281 break; 282 #endif 283 default: 284 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 285 break; 286 } 287 } 288 289 290 /* 291 * Process some data. 292 * This handles the simple case where no context is required. 293 */ 294 295 METHODDEF(void) 296 process_data_simple_main(j_decompress_ptr cinfo, _JSAMPARRAY output_buf, 297 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail) 298 { 299 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 300 JDIMENSION rowgroups_avail; 301 302 /* Read input data if we haven't filled the main buffer yet */ 303 if (!main_ptr->buffer_full) { 304 if (!(*cinfo->coef->_decompress_data) (cinfo, main_ptr->buffer)) 305 return; /* suspension forced, can do nothing more */ 306 main_ptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 307 } 308 309 /* There are always min_DCT_scaled_size row groups in an iMCU row. */ 310 rowgroups_avail = (JDIMENSION)cinfo->_min_DCT_scaled_size; 311 /* Note: at the bottom of the image, we may pass extra garbage row groups 312 * to the postprocessor. The postprocessor has to check for bottom 313 * of image anyway (at row resolution), so no point in us doing it too. 314 */ 315 316 /* Feed the postprocessor */ 317 (*cinfo->post->_post_process_data) (cinfo, main_ptr->buffer, 318 &main_ptr->rowgroup_ctr, rowgroups_avail, 319 output_buf, out_row_ctr, out_rows_avail); 320 321 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */ 322 if (main_ptr->rowgroup_ctr >= rowgroups_avail) { 323 main_ptr->buffer_full = FALSE; 324 main_ptr->rowgroup_ctr = 0; 325 } 326 } 327 328 329 /* 330 * Process some data. 331 * This handles the case where context rows must be provided. 332 */ 333 334 METHODDEF(void) 335 process_data_context_main(j_decompress_ptr cinfo, _JSAMPARRAY output_buf, 336 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail) 337 { 338 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 339 340 /* Read input data if we haven't filled the main buffer yet */ 341 if (!main_ptr->buffer_full) { 342 if (!(*cinfo->coef->_decompress_data) (cinfo, 343 main_ptr->xbuffer[main_ptr->whichptr])) 344 return; /* suspension forced, can do nothing more */ 345 main_ptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 346 main_ptr->iMCU_row_ctr++; /* count rows received */ 347 } 348 349 /* Postprocessor typically will not swallow all the input data it is handed 350 * in one call (due to filling the output buffer first). Must be prepared 351 * to exit and restart. This switch lets us keep track of how far we got. 352 * Note that each case falls through to the next on successful completion. 353 */ 354 switch (main_ptr->context_state) { 355 case CTX_POSTPONED_ROW: 356 /* Call postprocessor using previously set pointers for postponed row */ 357 (*cinfo->post->_post_process_data) (cinfo, 358 main_ptr->xbuffer[main_ptr->whichptr], 359 &main_ptr->rowgroup_ctr, 360 main_ptr->rowgroups_avail, output_buf, 361 out_row_ctr, out_rows_avail); 362 if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail) 363 return; /* Need to suspend */ 364 main_ptr->context_state = CTX_PREPARE_FOR_IMCU; 365 if (*out_row_ctr >= out_rows_avail) 366 return; /* Postprocessor exactly filled output buf */ 367 FALLTHROUGH /*FALLTHROUGH*/ 368 case CTX_PREPARE_FOR_IMCU: 369 /* Prepare to process first M-1 row groups of this iMCU row */ 370 main_ptr->rowgroup_ctr = 0; 371 main_ptr->rowgroups_avail = (JDIMENSION)(cinfo->_min_DCT_scaled_size - 1); 372 /* Check for bottom of image: if so, tweak pointers to "duplicate" 373 * the last sample row, and adjust rowgroups_avail to ignore padding rows. 374 */ 375 if (main_ptr->iMCU_row_ctr == cinfo->total_iMCU_rows) 376 set_bottom_pointers(cinfo); 377 main_ptr->context_state = CTX_PROCESS_IMCU; 378 FALLTHROUGH /*FALLTHROUGH*/ 379 case CTX_PROCESS_IMCU: 380 /* Call postprocessor using previously set pointers */ 381 (*cinfo->post->_post_process_data) (cinfo, 382 main_ptr->xbuffer[main_ptr->whichptr], 383 &main_ptr->rowgroup_ctr, 384 main_ptr->rowgroups_avail, output_buf, 385 out_row_ctr, out_rows_avail); 386 if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail) 387 return; /* Need to suspend */ 388 /* After the first iMCU, change wraparound pointers to normal state */ 389 if (main_ptr->iMCU_row_ctr == 1) 390 set_wraparound_pointers(cinfo); 391 /* Prepare to load new iMCU row using other xbuffer list */ 392 main_ptr->whichptr ^= 1; /* 0=>1 or 1=>0 */ 393 main_ptr->buffer_full = FALSE; 394 /* Still need to process last row group of this iMCU row, */ 395 /* which is saved at index M+1 of the other xbuffer */ 396 main_ptr->rowgroup_ctr = (JDIMENSION)(cinfo->_min_DCT_scaled_size + 1); 397 main_ptr->rowgroups_avail = (JDIMENSION)(cinfo->_min_DCT_scaled_size + 2); 398 main_ptr->context_state = CTX_POSTPONED_ROW; 399 } 400 } 401 402 403 /* 404 * Process some data. 405 * Final pass of two-pass quantization: just call the postprocessor. 406 * Source data will be the postprocessor controller's internal buffer. 407 */ 408 409 #ifdef QUANT_2PASS_SUPPORTED 410 411 METHODDEF(void) 412 process_data_crank_post(j_decompress_ptr cinfo, _JSAMPARRAY output_buf, 413 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail) 414 { 415 (*cinfo->post->_post_process_data) (cinfo, (_JSAMPIMAGE)NULL, 416 (JDIMENSION *)NULL, (JDIMENSION)0, 417 output_buf, out_row_ctr, out_rows_avail); 418 } 419 420 #endif /* QUANT_2PASS_SUPPORTED */ 421 422 423 /* 424 * Initialize main buffer controller. 425 */ 426 427 GLOBAL(void) 428 _jinit_d_main_controller(j_decompress_ptr cinfo, boolean need_full_buffer) 429 { 430 my_main_ptr main_ptr; 431 int ci, rgroup, ngroups; 432 jpeg_component_info *compptr; 433 434 if (cinfo->data_precision != BITS_IN_JSAMPLE) 435 ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision); 436 437 main_ptr = (my_main_ptr) 438 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 439 sizeof(my_main_controller)); 440 cinfo->main = (struct jpeg_d_main_controller *)main_ptr; 441 main_ptr->pub.start_pass = start_pass_main; 442 443 if (need_full_buffer) /* shouldn't happen */ 444 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 445 446 /* Allocate the workspace. 447 * ngroups is the number of row groups we need. 448 */ 449 if (cinfo->upsample->need_context_rows) { 450 if (cinfo->_min_DCT_scaled_size < 2) /* unsupported, see comments above */ 451 ERREXIT(cinfo, JERR_NOTIMPL); 452 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */ 453 ngroups = cinfo->_min_DCT_scaled_size + 2; 454 } else { 455 ngroups = cinfo->_min_DCT_scaled_size; 456 } 457 458 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 459 ci++, compptr++) { 460 rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) / 461 cinfo->_min_DCT_scaled_size; /* height of a row group of component */ 462 main_ptr->buffer[ci] = (_JSAMPARRAY)(*cinfo->mem->alloc_sarray) 463 ((j_common_ptr)cinfo, JPOOL_IMAGE, 464 compptr->width_in_blocks * compptr->_DCT_scaled_size, 465 (JDIMENSION)(rgroup * ngroups)); 466 } 467 } 468 469 #endif /* BITS_IN_JSAMPLE != 16 || defined(D_LOSSLESS_SUPPORTED) */