jdmainct.cpp (22513B)
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 my_main_ptr main = (my_main_ptr) cinfo->main; 162 int ci, rgroup; 163 int M = cinfo->min_DCT_scaled_size; 164 jpeg_component_info * compptr; 165 JSAMPARRAY xbuf; 166 167 /* Get top-level space for component array pointers. 168 * We alloc both arrays with one call to save a few cycles. 169 */ 170 main->xbuffer[0] = (JSAMPIMAGE) 171 ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE, 172 cinfo->num_components * 2 * SIZEOF( JSAMPARRAY ) ); 173 main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components; 174 175 for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 176 ci++, compptr++ ) { 177 rgroup = ( compptr->v_samp_factor * compptr->DCT_scaled_size ) / 178 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 179 /* Get space for pointer lists --- M+4 row groups in each list. 180 * We alloc both pointer lists with one call to save a few cycles. 181 */ 182 xbuf = (JSAMPARRAY) 183 ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE, 184 2 * ( rgroup * ( M + 4 ) ) * SIZEOF( JSAMPROW ) ); 185 xbuf += rgroup; /* want one row group at negative offsets */ 186 main->xbuffer[0][ci] = xbuf; 187 xbuf += rgroup * ( M + 4 ); 188 main->xbuffer[1][ci] = xbuf; 189 } 190 } 191 192 193 LOCAL void 194 make_funny_pointers( j_decompress_ptr cinfo ) { 195 /* Create the funny pointer lists discussed in the comments above. 196 * The actual workspace is already allocated (in main->buffer), 197 * and the space for the pointer lists is allocated too. 198 * This routine just fills in the curiously ordered lists. 199 * This will be repeated at the beginning of each pass. 200 */ 201 my_main_ptr main = (my_main_ptr) cinfo->main; 202 int ci, i, rgroup; 203 int M = cinfo->min_DCT_scaled_size; 204 jpeg_component_info * compptr; 205 JSAMPARRAY buf, xbuf0, xbuf1; 206 207 for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 208 ci++, compptr++ ) { 209 rgroup = ( compptr->v_samp_factor * compptr->DCT_scaled_size ) / 210 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 211 xbuf0 = main->xbuffer[0][ci]; 212 xbuf1 = main->xbuffer[1][ci]; 213 /* First copy the workspace pointers as-is */ 214 buf = main->buffer[ci]; 215 for ( i = 0; i < rgroup * ( M + 2 ); i++ ) { 216 xbuf0[i] = xbuf1[i] = buf[i]; 217 } 218 /* In the second list, put the last four row groups in swapped order */ 219 for ( i = 0; i < rgroup * 2; i++ ) { 220 xbuf1[rgroup * ( M - 2 ) + i] = buf[rgroup * M + i]; 221 xbuf1[rgroup * M + i] = buf[rgroup * ( M - 2 ) + i]; 222 } 223 /* The wraparound pointers at top and bottom will be filled later 224 * (see set_wraparound_pointers, below). Initially we want the "above" 225 * pointers to duplicate the first actual data line. This only needs 226 * to happen in xbuffer[0]. 227 */ 228 for ( i = 0; i < rgroup; i++ ) { 229 xbuf0[i - rgroup] = xbuf0[0]; 230 } 231 } 232 } 233 234 235 LOCAL void 236 set_wraparound_pointers( j_decompress_ptr cinfo ) { 237 /* Set up the "wraparound" pointers at top and bottom of the pointer lists. 238 * This changes the pointer list state from top-of-image to the normal state. 239 */ 240 my_main_ptr main = (my_main_ptr) cinfo->main; 241 int ci, i, rgroup; 242 int M = cinfo->min_DCT_scaled_size; 243 jpeg_component_info * compptr; 244 JSAMPARRAY xbuf0, xbuf1; 245 246 for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 247 ci++, compptr++ ) { 248 rgroup = ( compptr->v_samp_factor * compptr->DCT_scaled_size ) / 249 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 250 xbuf0 = main->xbuffer[0][ci]; 251 xbuf1 = main->xbuffer[1][ci]; 252 for ( i = 0; i < rgroup; i++ ) { 253 xbuf0[i - rgroup] = xbuf0[rgroup * ( M + 1 ) + i]; 254 xbuf1[i - rgroup] = xbuf1[rgroup * ( M + 1 ) + i]; 255 xbuf0[rgroup * ( M + 2 ) + i] = xbuf0[i]; 256 xbuf1[rgroup * ( M + 2 ) + i] = xbuf1[i]; 257 } 258 } 259 } 260 261 262 LOCAL void 263 set_bottom_pointers( j_decompress_ptr cinfo ) { 264 /* Change the pointer lists to duplicate the last sample row at the bottom 265 * of the image. whichptr indicates which xbuffer holds the final iMCU row. 266 * Also sets rowgroups_avail to indicate number of nondummy row groups in row. 267 */ 268 my_main_ptr main = (my_main_ptr) cinfo->main; 269 int ci, i, rgroup, iMCUheight, rows_left; 270 jpeg_component_info * compptr; 271 JSAMPARRAY xbuf; 272 273 for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 274 ci++, compptr++ ) { 275 /* Count sample rows in one iMCU row and in one row group */ 276 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size; 277 rgroup = iMCUheight / cinfo->min_DCT_scaled_size; 278 /* Count nondummy sample rows remaining for this component */ 279 rows_left = (int) ( compptr->downsampled_height % (JDIMENSION) iMCUheight ); 280 if ( rows_left == 0 ) { 281 rows_left = iMCUheight; 282 } 283 /* Count nondummy row groups. Should get same answer for each component, 284 * so we need only do it once. 285 */ 286 if ( ci == 0 ) { 287 main->rowgroups_avail = (JDIMENSION) ( ( rows_left - 1 ) / rgroup + 1 ); 288 } 289 /* Duplicate the last real sample row rgroup*2 times; this pads out the 290 * last partial rowgroup and ensures at least one full rowgroup of context. 291 */ 292 xbuf = main->xbuffer[main->whichptr][ci]; 293 for ( i = 0; i < rgroup * 2; i++ ) { 294 xbuf[rows_left + i] = xbuf[rows_left - 1]; 295 } 296 } 297 } 298 299 300 /* 301 * Initialize for a processing pass. 302 */ 303 304 METHODDEF void 305 start_pass_main( j_decompress_ptr cinfo, J_BUF_MODE pass_mode ) { 306 my_main_ptr main = (my_main_ptr) cinfo->main; 307 308 switch ( pass_mode ) { 309 case JBUF_PASS_THRU: 310 if ( cinfo->upsample->need_context_rows ) { 311 main->pub.process_data = process_data_context_main; 312 make_funny_pointers( cinfo );/* Create the xbuffer[] lists */ 313 main->whichptr = 0;/* Read first iMCU row into xbuffer[0] */ 314 main->context_state = CTX_PREPARE_FOR_IMCU; 315 main->iMCU_row_ctr = 0; 316 } else { 317 /* Simple case with no context needed */ 318 main->pub.process_data = process_data_simple_main; 319 } 320 main->buffer_full = FALSE;/* Mark buffer empty */ 321 main->rowgroup_ctr = 0; 322 break; 323 #ifdef QUANT_2PASS_SUPPORTED 324 case JBUF_CRANK_DEST: 325 /* For last pass of 2-pass quantization, just crank the postprocessor */ 326 main->pub.process_data = process_data_crank_post; 327 break; 328 #endif 329 default: 330 ERREXIT( cinfo, JERR_BAD_BUFFER_MODE ); 331 break; 332 } 333 } 334 335 336 /* 337 * Process some data. 338 * This handles the simple case where no context is required. 339 */ 340 341 METHODDEF void 342 process_data_simple_main( j_decompress_ptr cinfo, 343 JSAMPARRAY output_buf, JDIMENSION * out_row_ctr, 344 JDIMENSION out_rows_avail ) { 345 my_main_ptr main = (my_main_ptr) cinfo->main; 346 JDIMENSION rowgroups_avail; 347 348 /* Read input data if we haven't filled the main buffer yet */ 349 if ( !main->buffer_full ) { 350 if ( !( *cinfo->coef->decompress_data )( cinfo, main->buffer ) ) { 351 return; 352 } /* suspension forced, can do nothing more */ 353 main->buffer_full = TRUE;/* OK, we have an iMCU row to work with */ 354 } 355 356 /* There are always min_DCT_scaled_size row groups in an iMCU row. */ 357 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size; 358 /* Note: at the bottom of the image, we may pass extra garbage row groups 359 * to the postprocessor. The postprocessor has to check for bottom 360 * of image anyway (at row resolution), so no point in us doing it too. 361 */ 362 363 /* Feed the postprocessor */ 364 ( *cinfo->post->post_process_data )( cinfo, main->buffer, 365 &main->rowgroup_ctr, rowgroups_avail, 366 output_buf, out_row_ctr, out_rows_avail ); 367 368 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */ 369 if ( main->rowgroup_ctr >= rowgroups_avail ) { 370 main->buffer_full = FALSE; 371 main->rowgroup_ctr = 0; 372 } 373 } 374 375 376 /* 377 * Process some data. 378 * This handles the case where context rows must be provided. 379 */ 380 381 METHODDEF void 382 process_data_context_main( j_decompress_ptr cinfo, 383 JSAMPARRAY output_buf, JDIMENSION * out_row_ctr, 384 JDIMENSION out_rows_avail ) { 385 my_main_ptr main = (my_main_ptr) cinfo->main; 386 387 /* Read input data if we haven't filled the main buffer yet */ 388 if ( !main->buffer_full ) { 389 if ( !( *cinfo->coef->decompress_data )( cinfo, 390 main->xbuffer[main->whichptr] ) ) { 391 return; 392 } /* suspension forced, can do nothing more */ 393 main->buffer_full = TRUE;/* OK, we have an iMCU row to work with */ 394 main->iMCU_row_ctr++; /* count rows received */ 395 } 396 397 /* Postprocessor typically will not swallow all the input data it is handed 398 * in one call (due to filling the output buffer first). Must be prepared 399 * to exit and restart. This switch lets us keep track of how far we got. 400 * Note that each case falls through to the next on successful completion. 401 */ 402 switch ( main->context_state ) { 403 case CTX_POSTPONED_ROW: 404 /* Call postprocessor using previously set pointers for postponed row */ 405 ( *cinfo->post->post_process_data )( cinfo, main->xbuffer[main->whichptr], 406 &main->rowgroup_ctr, main->rowgroups_avail, 407 output_buf, out_row_ctr, out_rows_avail ); 408 if ( main->rowgroup_ctr < main->rowgroups_avail ) { 409 return; 410 } /* Need to suspend */ 411 main->context_state = CTX_PREPARE_FOR_IMCU; 412 if ( *out_row_ctr >= out_rows_avail ) { 413 return; 414 } /* Postprocessor exactly filled output buf */ 415 /*FALLTHROUGH*/ 416 case CTX_PREPARE_FOR_IMCU: 417 /* Prepare to process first M-1 row groups of this iMCU row */ 418 main->rowgroup_ctr = 0; 419 main->rowgroups_avail = (JDIMENSION) ( cinfo->min_DCT_scaled_size - 1 ); 420 /* Check for bottom of image: if so, tweak pointers to "duplicate" 421 * the last sample row, and adjust rowgroups_avail to ignore padding rows. 422 */ 423 if ( main->iMCU_row_ctr == cinfo->total_iMCU_rows ) { 424 set_bottom_pointers( cinfo ); 425 } 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; 435 } /* Need to suspend */ 436 /* After the first iMCU, change wraparound pointers to normal state */ 437 if ( main->iMCU_row_ctr == 1 ) { 438 set_wraparound_pointers( cinfo ); 439 } 440 /* Prepare to load new iMCU row using other xbuffer list */ 441 main->whichptr ^= 1;/* 0=>1 or 1=>0 */ 442 main->buffer_full = FALSE; 443 /* Still need to process last row group of this iMCU row, */ 444 /* which is saved at index M+1 of the other xbuffer */ 445 main->rowgroup_ctr = (JDIMENSION) ( cinfo->min_DCT_scaled_size + 1 ); 446 main->rowgroups_avail = (JDIMENSION) ( cinfo->min_DCT_scaled_size + 2 ); 447 main->context_state = CTX_POSTPONED_ROW; 448 } 449 } 450 451 452 /* 453 * Process some data. 454 * Final pass of two-pass quantization: just call the postprocessor. 455 * Source data will be the postprocessor controller's internal buffer. 456 */ 457 458 #ifdef QUANT_2PASS_SUPPORTED 459 460 METHODDEF void 461 process_data_crank_post( j_decompress_ptr cinfo, 462 JSAMPARRAY output_buf, JDIMENSION * out_row_ctr, 463 JDIMENSION out_rows_avail ) { 464 ( *cinfo->post->post_process_data )( cinfo, (JSAMPIMAGE) NULL, 465 (JDIMENSION *) NULL, (JDIMENSION) 0, 466 output_buf, out_row_ctr, out_rows_avail ); 467 } 468 469 #endif /* QUANT_2PASS_SUPPORTED */ 470 471 472 /* 473 * Initialize main buffer controller. 474 */ 475 476 GLOBAL void 477 jinit_d_main_controller( j_decompress_ptr cinfo, boolean need_full_buffer ) { 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 } 491 492 /* Allocate the workspace. 493 * ngroups is the number of row groups we need. 494 */ 495 if ( cinfo->upsample->need_context_rows ) { 496 if ( cinfo->min_DCT_scaled_size < 2 ) {/* unsupported, see comments above */ 497 ERREXIT( cinfo, JERR_NOTIMPL ); 498 } 499 alloc_funny_pointers( cinfo );/* Alloc space for xbuffer[] lists */ 500 ngroups = cinfo->min_DCT_scaled_size + 2; 501 } else { 502 ngroups = cinfo->min_DCT_scaled_size; 503 } 504 505 for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 506 ci++, compptr++ ) { 507 rgroup = ( compptr->v_samp_factor * compptr->DCT_scaled_size ) / 508 cinfo->min_DCT_scaled_size; /* height of a row group of component */ 509 main->buffer[ci] = ( *cinfo->mem->alloc_sarray ) 510 ( (j_common_ptr) cinfo, JPOOL_IMAGE, 511 compptr->width_in_blocks * compptr->DCT_scaled_size, 512 (JDIMENSION) ( rgroup * ngroups ) ); 513 } 514 }