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 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 /* Forward declarations */ 115 METHODDEF(void) process_data_simple_main(j_decompress_ptr cinfo, 116 JSAMPARRAY output_buf, 117 JDIMENSION *out_row_ctr, 118 JDIMENSION out_rows_avail); 119 METHODDEF(void) process_data_context_main(j_decompress_ptr cinfo, 120 JSAMPARRAY output_buf, 121 JDIMENSION *out_row_ctr, 122 JDIMENSION out_rows_avail); 123 #ifdef QUANT_2PASS_SUPPORTED 124 METHODDEF(void) process_data_crank_post(j_decompress_ptr cinfo, 125 JSAMPARRAY output_buf, 126 JDIMENSION *out_row_ctr, 127 JDIMENSION out_rows_avail); 128 #endif 129 130 131 LOCAL(void) 132 alloc_funny_pointers(j_decompress_ptr cinfo) 133 /* Allocate space for the funny pointer lists. 134 * This is done only once, not once per pass. 135 */ 136 { 137 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 138 int ci, rgroup; 139 int M = cinfo->_min_DCT_scaled_size; 140 jpeg_component_info *compptr; 141 JSAMPARRAY xbuf; 142 143 /* Get top-level space for component array pointers. 144 * We alloc both arrays with one call to save a few cycles. 145 */ 146 main_ptr->xbuffer[0] = (JSAMPIMAGE) 147 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 148 cinfo->num_components * 2 * sizeof(JSAMPARRAY)); 149 main_ptr->xbuffer[1] = main_ptr->xbuffer[0] + cinfo->num_components; 150 151 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 152 ci++, compptr++) { 153 rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) / 154 cinfo->_min_DCT_scaled_size; /* height of a row group of component */ 155 /* Get space for pointer lists --- M+4 row groups in each list. 156 * We alloc both pointer lists with one call to save a few cycles. 157 */ 158 xbuf = (JSAMPARRAY) 159 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 160 2 * (rgroup * (M + 4)) * sizeof(JSAMPROW)); 161 xbuf += rgroup; /* want one row group at negative offsets */ 162 main_ptr->xbuffer[0][ci] = xbuf; 163 xbuf += rgroup * (M + 4); 164 main_ptr->xbuffer[1][ci] = xbuf; 165 } 166 } 167 168 169 LOCAL(void) 170 make_funny_pointers(j_decompress_ptr cinfo) 171 /* Create the funny pointer lists discussed in the comments above. 172 * The actual workspace is already allocated (in main_ptr->buffer), 173 * and the space for the pointer lists is allocated too. 174 * This routine just fills in the curiously ordered lists. 175 * This will be repeated at the beginning of each pass. 176 */ 177 { 178 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 179 int ci, i, rgroup; 180 int M = cinfo->_min_DCT_scaled_size; 181 jpeg_component_info *compptr; 182 JSAMPARRAY buf, xbuf0, xbuf1; 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 xbuf0 = main_ptr->xbuffer[0][ci]; 189 xbuf1 = main_ptr->xbuffer[1][ci]; 190 /* First copy the workspace pointers as-is */ 191 buf = main_ptr->buffer[ci]; 192 for (i = 0; i < rgroup * (M + 2); i++) { 193 xbuf0[i] = xbuf1[i] = buf[i]; 194 } 195 /* In the second list, put the last four row groups in swapped order */ 196 for (i = 0; i < rgroup * 2; i++) { 197 xbuf1[rgroup * (M - 2) + i] = buf[rgroup * M + i]; 198 xbuf1[rgroup * M + i] = buf[rgroup * (M - 2) + i]; 199 } 200 /* The wraparound pointers at top and bottom will be filled later 201 * (see set_wraparound_pointers, below). Initially we want the "above" 202 * pointers to duplicate the first actual data line. This only needs 203 * to happen in xbuffer[0]. 204 */ 205 for (i = 0; i < rgroup; i++) { 206 xbuf0[i - rgroup] = xbuf0[0]; 207 } 208 } 209 } 210 211 212 LOCAL(void) 213 set_bottom_pointers(j_decompress_ptr cinfo) 214 /* Change the pointer lists to duplicate the last sample row at the bottom 215 * of the image. whichptr indicates which xbuffer holds the final iMCU row. 216 * Also sets rowgroups_avail to indicate number of nondummy row groups in row. 217 */ 218 { 219 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 220 int ci, i, rgroup, iMCUheight, rows_left; 221 jpeg_component_info *compptr; 222 JSAMPARRAY xbuf; 223 224 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 225 ci++, compptr++) { 226 /* Count sample rows in one iMCU row and in one row group */ 227 iMCUheight = compptr->v_samp_factor * compptr->_DCT_scaled_size; 228 rgroup = iMCUheight / cinfo->_min_DCT_scaled_size; 229 /* Count nondummy sample rows remaining for this component */ 230 rows_left = (int)(compptr->downsampled_height % (JDIMENSION)iMCUheight); 231 if (rows_left == 0) rows_left = iMCUheight; 232 /* Count nondummy row groups. Should get same answer for each component, 233 * so we need only do it once. 234 */ 235 if (ci == 0) { 236 main_ptr->rowgroups_avail = (JDIMENSION)((rows_left - 1) / rgroup + 1); 237 } 238 /* Duplicate the last real sample row rgroup*2 times; this pads out the 239 * last partial rowgroup and ensures at least one full rowgroup of context. 240 */ 241 xbuf = main_ptr->xbuffer[main_ptr->whichptr][ci]; 242 for (i = 0; i < rgroup * 2; i++) { 243 xbuf[rows_left + i] = xbuf[rows_left - 1]; 244 } 245 } 246 } 247 248 249 /* 250 * Initialize for a processing pass. 251 */ 252 253 METHODDEF(void) 254 start_pass_main(j_decompress_ptr cinfo, J_BUF_MODE pass_mode) 255 { 256 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 257 258 switch (pass_mode) { 259 case JBUF_PASS_THRU: 260 if (cinfo->upsample->need_context_rows) { 261 main_ptr->pub.process_data = process_data_context_main; 262 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */ 263 main_ptr->whichptr = 0; /* Read first iMCU row into xbuffer[0] */ 264 main_ptr->context_state = CTX_PREPARE_FOR_IMCU; 265 main_ptr->iMCU_row_ctr = 0; 266 } else { 267 /* Simple case with no context needed */ 268 main_ptr->pub.process_data = process_data_simple_main; 269 } 270 main_ptr->buffer_full = FALSE; /* Mark buffer empty */ 271 main_ptr->rowgroup_ctr = 0; 272 break; 273 #ifdef QUANT_2PASS_SUPPORTED 274 case JBUF_CRANK_DEST: 275 /* For last pass of 2-pass quantization, just crank the postprocessor */ 276 main_ptr->pub.process_data = process_data_crank_post; 277 break; 278 #endif 279 default: 280 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 281 break; 282 } 283 } 284 285 286 /* 287 * Process some data. 288 * This handles the simple case where no context is required. 289 */ 290 291 METHODDEF(void) 292 process_data_simple_main(j_decompress_ptr cinfo, JSAMPARRAY output_buf, 293 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail) 294 { 295 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 296 JDIMENSION rowgroups_avail; 297 298 /* Read input data if we haven't filled the main buffer yet */ 299 if (!main_ptr->buffer_full) { 300 if (!(*cinfo->coef->decompress_data) (cinfo, main_ptr->buffer)) 301 return; /* suspension forced, can do nothing more */ 302 main_ptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 303 } 304 305 /* There are always min_DCT_scaled_size row groups in an iMCU row. */ 306 rowgroups_avail = (JDIMENSION)cinfo->_min_DCT_scaled_size; 307 /* Note: at the bottom of the image, we may pass extra garbage row groups 308 * to the postprocessor. The postprocessor has to check for bottom 309 * of image anyway (at row resolution), so no point in us doing it too. 310 */ 311 312 /* Feed the postprocessor */ 313 (*cinfo->post->post_process_data) (cinfo, main_ptr->buffer, 314 &main_ptr->rowgroup_ctr, rowgroups_avail, 315 output_buf, out_row_ctr, out_rows_avail); 316 317 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */ 318 if (main_ptr->rowgroup_ctr >= rowgroups_avail) { 319 main_ptr->buffer_full = FALSE; 320 main_ptr->rowgroup_ctr = 0; 321 } 322 } 323 324 325 /* 326 * Process some data. 327 * This handles the case where context rows must be provided. 328 */ 329 330 METHODDEF(void) 331 process_data_context_main(j_decompress_ptr cinfo, JSAMPARRAY output_buf, 332 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail) 333 { 334 my_main_ptr main_ptr = (my_main_ptr)cinfo->main; 335 336 /* Read input data if we haven't filled the main buffer yet */ 337 if (!main_ptr->buffer_full) { 338 if (!(*cinfo->coef->decompress_data) (cinfo, 339 main_ptr->xbuffer[main_ptr->whichptr])) 340 return; /* suspension forced, can do nothing more */ 341 main_ptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */ 342 main_ptr->iMCU_row_ctr++; /* count rows received */ 343 } 344 345 /* Postprocessor typically will not swallow all the input data it is handed 346 * in one call (due to filling the output buffer first). Must be prepared 347 * to exit and restart. This switch lets us keep track of how far we got. 348 * Note that each case falls through to the next on successful completion. 349 */ 350 switch (main_ptr->context_state) { 351 case CTX_POSTPONED_ROW: 352 /* Call postprocessor using previously set pointers for postponed row */ 353 (*cinfo->post->post_process_data) (cinfo, 354 main_ptr->xbuffer[main_ptr->whichptr], 355 &main_ptr->rowgroup_ctr, 356 main_ptr->rowgroups_avail, output_buf, 357 out_row_ctr, out_rows_avail); 358 if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail) 359 return; /* Need to suspend */ 360 main_ptr->context_state = CTX_PREPARE_FOR_IMCU; 361 if (*out_row_ctr >= out_rows_avail) 362 return; /* Postprocessor exactly filled output buf */ 363 /*FALLTHROUGH*/ 364 case CTX_PREPARE_FOR_IMCU: 365 /* Prepare to process first M-1 row groups of this iMCU row */ 366 main_ptr->rowgroup_ctr = 0; 367 main_ptr->rowgroups_avail = (JDIMENSION)(cinfo->_min_DCT_scaled_size - 1); 368 /* Check for bottom of image: if so, tweak pointers to "duplicate" 369 * the last sample row, and adjust rowgroups_avail to ignore padding rows. 370 */ 371 if (main_ptr->iMCU_row_ctr == cinfo->total_iMCU_rows) 372 set_bottom_pointers(cinfo); 373 main_ptr->context_state = CTX_PROCESS_IMCU; 374 /*FALLTHROUGH*/ 375 case CTX_PROCESS_IMCU: 376 /* Call postprocessor using previously set pointers */ 377 (*cinfo->post->post_process_data) (cinfo, 378 main_ptr->xbuffer[main_ptr->whichptr], 379 &main_ptr->rowgroup_ctr, 380 main_ptr->rowgroups_avail, output_buf, 381 out_row_ctr, out_rows_avail); 382 if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail) 383 return; /* Need to suspend */ 384 /* After the first iMCU, change wraparound pointers to normal state */ 385 if (main_ptr->iMCU_row_ctr == 1) 386 set_wraparound_pointers(cinfo); 387 /* Prepare to load new iMCU row using other xbuffer list */ 388 main_ptr->whichptr ^= 1; /* 0=>1 or 1=>0 */ 389 main_ptr->buffer_full = FALSE; 390 /* Still need to process last row group of this iMCU row, */ 391 /* which is saved at index M+1 of the other xbuffer */ 392 main_ptr->rowgroup_ctr = (JDIMENSION)(cinfo->_min_DCT_scaled_size + 1); 393 main_ptr->rowgroups_avail = (JDIMENSION)(cinfo->_min_DCT_scaled_size + 2); 394 main_ptr->context_state = CTX_POSTPONED_ROW; 395 } 396 } 397 398 399 /* 400 * Process some data. 401 * Final pass of two-pass quantization: just call the postprocessor. 402 * Source data will be the postprocessor controller's internal buffer. 403 */ 404 405 #ifdef QUANT_2PASS_SUPPORTED 406 407 METHODDEF(void) 408 process_data_crank_post(j_decompress_ptr cinfo, JSAMPARRAY output_buf, 409 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail) 410 { 411 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE)NULL, 412 (JDIMENSION *)NULL, (JDIMENSION)0, 413 output_buf, out_row_ctr, out_rows_avail); 414 } 415 416 #endif /* QUANT_2PASS_SUPPORTED */ 417 418 419 /* 420 * Initialize main buffer controller. 421 */ 422 423 GLOBAL(void) 424 jinit_d_main_controller(j_decompress_ptr cinfo, boolean need_full_buffer) 425 { 426 my_main_ptr main_ptr; 427 int ci, rgroup, ngroups; 428 jpeg_component_info *compptr; 429 430 main_ptr = (my_main_ptr) 431 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 432 sizeof(my_main_controller)); 433 cinfo->main = (struct jpeg_d_main_controller *)main_ptr; 434 main_ptr->pub.start_pass = start_pass_main; 435 436 if (need_full_buffer) /* shouldn't happen */ 437 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 438 439 /* Allocate the workspace. 440 * ngroups is the number of row groups we need. 441 */ 442 if (cinfo->upsample->need_context_rows) { 443 if (cinfo->_min_DCT_scaled_size < 2) /* unsupported, see comments above */ 444 ERREXIT(cinfo, JERR_NOTIMPL); 445 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */ 446 ngroups = cinfo->_min_DCT_scaled_size + 2; 447 } else { 448 ngroups = cinfo->_min_DCT_scaled_size; 449 } 450 451 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 452 ci++, compptr++) { 453 rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) / 454 cinfo->_min_DCT_scaled_size; /* height of a row group of component */ 455 main_ptr->buffer[ci] = (*cinfo->mem->alloc_sarray) 456 ((j_common_ptr)cinfo, JPOOL_IMAGE, 457 compptr->width_in_blocks * compptr->_DCT_scaled_size, 458 (JDIMENSION)(rgroup * ngroups)); 459 } 460 } 461
