2 * CDE - Common Desktop Environment
4 * Copyright (c) 1993-2012, The Open Group. All rights reserved.
6 * These libraries and programs are free software; you can
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8 * Lesser General Public License as published by the Free Software
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15 * PURPOSE. See the GNU Lesser General Public License for more
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23 /* $XConsortium: jdmainct.c /main/2 1996/05/09 03:48:30 drk $ */
27 * Copyright (C) 1994-1996, Thomas G. Lane.
28 * This file is part of the Independent JPEG Group's software.
29 * For conditions of distribution and use, see the accompanying README file.
31 * This file contains the main buffer controller for decompression.
32 * The main buffer lies between the JPEG decompressor proper and the
33 * post-processor; it holds downsampled data in the JPEG colorspace.
35 * Note that this code is bypassed in raw-data mode, since the application
36 * supplies the equivalent of the main buffer in that case.
39 #define JPEG_INTERNALS
45 * In the current system design, the main buffer need never be a full-image
46 * buffer; any full-height buffers will be found inside the coefficient or
47 * postprocessing controllers. Nonetheless, the main controller is not
48 * trivial. Its responsibility is to provide context rows for upsampling/
49 * rescaling, and doing this in an efficient fashion is a bit tricky.
51 * Postprocessor input data is counted in "row groups". A row group
52 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
53 * sample rows of each component. (We require DCT_scaled_size values to be
54 * chosen such that these numbers are integers. In practice DCT_scaled_size
55 * values will likely be powers of two, so we actually have the stronger
56 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
57 * Upsampling will typically produce max_v_samp_factor pixel rows from each
58 * row group (times any additional scale factor that the upsampler is
61 * The coefficient controller will deliver data to us one iMCU row at a time;
62 * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
63 * exactly min_DCT_scaled_size row groups. (This amount of data corresponds
64 * to one row of MCUs when the image is fully interleaved.) Note that the
65 * number of sample rows varies across components, but the number of row
66 * groups does not. Some garbage sample rows may be included in the last iMCU
67 * row at the bottom of the image.
69 * Depending on the vertical scaling algorithm used, the upsampler may need
70 * access to the sample row(s) above and below its current input row group.
71 * The upsampler is required to set need_context_rows TRUE at global selection
72 * time if so. When need_context_rows is FALSE, this controller can simply
73 * obtain one iMCU row at a time from the coefficient controller and dole it
74 * out as row groups to the postprocessor.
76 * When need_context_rows is TRUE, this controller guarantees that the buffer
77 * passed to postprocessing contains at least one row group's worth of samples
78 * above and below the row group(s) being processed. Note that the context
79 * rows "above" the first passed row group appear at negative row offsets in
80 * the passed buffer. At the top and bottom of the image, the required
81 * context rows are manufactured by duplicating the first or last real sample
82 * row; this avoids having special cases in the upsampling inner loops.
84 * The amount of context is fixed at one row group just because that's a
85 * convenient number for this controller to work with. The existing
86 * upsamplers really only need one sample row of context. An upsampler
87 * supporting arbitrary output rescaling might wish for more than one row
88 * group of context when shrinking the image; tough, we don't handle that.
89 * (This is justified by the assumption that downsizing will be handled mostly
90 * by adjusting the DCT_scaled_size values, so that the actual scale factor at
91 * the upsample step needn't be much less than one.)
93 * To provide the desired context, we have to retain the last two row groups
94 * of one iMCU row while reading in the next iMCU row. (The last row group
95 * can't be processed until we have another row group for its below-context,
96 * and so we have to save the next-to-last group too for its above-context.)
97 * We could do this most simply by copying data around in our buffer, but
98 * that'd be very slow. We can avoid copying any data by creating a rather
99 * strange pointer structure. Here's how it works. We allocate a workspace
100 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
101 * of row groups per iMCU row). We create two sets of redundant pointers to
102 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
103 * pointer lists look like this:
105 * master pointer --> 0 master pointer --> 0
114 * We read alternate iMCU rows using each master pointer; thus the last two
115 * row groups of the previous iMCU row remain un-overwritten in the workspace.
116 * The pointer lists are set up so that the required context rows appear to
117 * be adjacent to the proper places when we pass the pointer lists to the
120 * The above pictures describe the normal state of the pointer lists.
121 * At top and bottom of the image, we diddle the pointer lists to duplicate
122 * the first or last sample row as necessary (this is cheaper than copying
123 * sample rows around).
125 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
126 * situation each iMCU row provides only one row group so the buffering logic
127 * must be different (eg, we must read two iMCU rows before we can emit the
128 * first row group). For now, we simply do not support providing context
129 * rows when min_DCT_scaled_size is 1. That combination seems unlikely to
130 * be worth providing --- if someone wants a 1/8th-size preview, they probably
131 * want it quick and dirty, so a context-free upsampler is sufficient.
135 /* Private buffer controller object */
138 struct jpeg_d_main_controller pub; /* public fields */
140 /* Pointer to allocated workspace (M or M+2 row groups). */
141 JSAMPARRAY buffer[MAX_COMPONENTS];
143 boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
144 JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
146 /* Remaining fields are only used in the context case. */
148 /* These are the master pointers to the funny-order pointer lists. */
149 JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
151 int whichptr; /* indicates which pointer set is now in use */
152 int context_state; /* process_data state machine status */
153 JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
154 JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */
155 } my_main_controller;
157 typedef my_main_controller * my_main_ptr;
159 /* context_state values: */
160 #define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
161 #define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
162 #define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
165 /* Forward declarations */
166 METHODDEF(void) process_data_simple_main
167 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
168 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
169 METHODDEF(void) process_data_context_main
170 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
171 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
172 #ifdef QUANT_2PASS_SUPPORTED
173 METHODDEF(void) process_data_crank_post
174 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
175 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
180 alloc_funny_pointers (j_decompress_ptr cinfo)
181 /* Allocate space for the funny pointer lists.
182 * This is done only once, not once per pass.
185 my_main_ptr main = (my_main_ptr) cinfo->main;
187 int M = cinfo->min_DCT_scaled_size;
188 jpeg_component_info *compptr;
191 /* Get top-level space for component array pointers.
192 * We alloc both arrays with one call to save a few cycles.
194 main->xbuffer[0] = (JSAMPIMAGE)
195 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
196 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
197 main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components;
199 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
201 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
202 cinfo->min_DCT_scaled_size; /* height of a row group of component */
203 /* Get space for pointer lists --- M+4 row groups in each list.
204 * We alloc both pointer lists with one call to save a few cycles.
207 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
208 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
209 xbuf += rgroup; /* want one row group at negative offsets */
210 main->xbuffer[0][ci] = xbuf;
211 xbuf += rgroup * (M + 4);
212 main->xbuffer[1][ci] = xbuf;
218 make_funny_pointers (j_decompress_ptr cinfo)
219 /* Create the funny pointer lists discussed in the comments above.
220 * The actual workspace is already allocated (in main->buffer),
221 * and the space for the pointer lists is allocated too.
222 * This routine just fills in the curiously ordered lists.
223 * This will be repeated at the beginning of each pass.
226 my_main_ptr main = (my_main_ptr) cinfo->main;
228 int M = cinfo->min_DCT_scaled_size;
229 jpeg_component_info *compptr;
230 JSAMPARRAY buf, xbuf0, xbuf1;
232 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
234 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
235 cinfo->min_DCT_scaled_size; /* height of a row group of component */
236 xbuf0 = main->xbuffer[0][ci];
237 xbuf1 = main->xbuffer[1][ci];
238 /* First copy the workspace pointers as-is */
239 buf = main->buffer[ci];
240 for (i = 0; i < rgroup * (M + 2); i++) {
241 xbuf0[i] = xbuf1[i] = buf[i];
243 /* In the second list, put the last four row groups in swapped order */
244 for (i = 0; i < rgroup * 2; i++) {
245 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
246 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
248 /* The wraparound pointers at top and bottom will be filled later
249 * (see set_wraparound_pointers, below). Initially we want the "above"
250 * pointers to duplicate the first actual data line. This only needs
251 * to happen in xbuffer[0].
253 for (i = 0; i < rgroup; i++) {
254 xbuf0[i - rgroup] = xbuf0[0];
261 set_wraparound_pointers (j_decompress_ptr cinfo)
262 /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
263 * This changes the pointer list state from top-of-image to the normal state.
266 my_main_ptr main = (my_main_ptr) cinfo->main;
268 int M = cinfo->min_DCT_scaled_size;
269 jpeg_component_info *compptr;
270 JSAMPARRAY xbuf0, xbuf1;
272 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
274 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
275 cinfo->min_DCT_scaled_size; /* height of a row group of component */
276 xbuf0 = main->xbuffer[0][ci];
277 xbuf1 = main->xbuffer[1][ci];
278 for (i = 0; i < rgroup; i++) {
279 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
280 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
281 xbuf0[rgroup*(M+2) + i] = xbuf0[i];
282 xbuf1[rgroup*(M+2) + i] = xbuf1[i];
289 set_bottom_pointers (j_decompress_ptr cinfo)
290 /* Change the pointer lists to duplicate the last sample row at the bottom
291 * of the image. whichptr indicates which xbuffer holds the final iMCU row.
292 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
295 my_main_ptr main = (my_main_ptr) cinfo->main;
296 int ci, i, rgroup, iMCUheight, rows_left;
297 jpeg_component_info *compptr;
300 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
302 /* Count sample rows in one iMCU row and in one row group */
303 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size;
304 rgroup = iMCUheight / cinfo->min_DCT_scaled_size;
305 /* Count nondummy sample rows remaining for this component */
306 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
307 if (rows_left == 0) rows_left = iMCUheight;
308 /* Count nondummy row groups. Should get same answer for each component,
309 * so we need only do it once.
312 main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
314 /* Duplicate the last real sample row rgroup*2 times; this pads out the
315 * last partial rowgroup and ensures at least one full rowgroup of context.
317 xbuf = main->xbuffer[main->whichptr][ci];
318 for (i = 0; i < rgroup * 2; i++) {
319 xbuf[rows_left + i] = xbuf[rows_left-1];
326 * Initialize for a processing pass.
330 start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
332 my_main_ptr main = (my_main_ptr) cinfo->main;
336 if (cinfo->upsample->need_context_rows) {
337 main->pub.process_data = process_data_context_main;
338 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
339 main->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
340 main->context_state = CTX_PREPARE_FOR_IMCU;
341 main->iMCU_row_ctr = 0;
343 /* Simple case with no context needed */
344 main->pub.process_data = process_data_simple_main;
346 main->buffer_full = FALSE; /* Mark buffer empty */
347 main->rowgroup_ctr = 0;
349 #ifdef QUANT_2PASS_SUPPORTED
350 case JBUF_CRANK_DEST:
351 /* For last pass of 2-pass quantization, just crank the postprocessor */
352 main->pub.process_data = process_data_crank_post;
356 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
364 * This handles the simple case where no context is required.
368 process_data_simple_main (j_decompress_ptr cinfo,
369 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
370 JDIMENSION out_rows_avail)
372 my_main_ptr main = (my_main_ptr) cinfo->main;
373 JDIMENSION rowgroups_avail;
375 /* Read input data if we haven't filled the main buffer yet */
376 if (! main->buffer_full) {
377 if (! (*cinfo->coef->decompress_data) (cinfo, main->buffer))
378 return; /* suspension forced, can do nothing more */
379 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
382 /* There are always min_DCT_scaled_size row groups in an iMCU row. */
383 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size;
384 /* Note: at the bottom of the image, we may pass extra garbage row groups
385 * to the postprocessor. The postprocessor has to check for bottom
386 * of image anyway (at row resolution), so no point in us doing it too.
389 /* Feed the postprocessor */
390 (*cinfo->post->post_process_data) (cinfo, main->buffer,
391 &main->rowgroup_ctr, rowgroups_avail,
392 output_buf, out_row_ctr, out_rows_avail);
394 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
395 if (main->rowgroup_ctr >= rowgroups_avail) {
396 main->buffer_full = FALSE;
397 main->rowgroup_ctr = 0;
404 * This handles the case where context rows must be provided.
408 process_data_context_main (j_decompress_ptr cinfo,
409 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
410 JDIMENSION out_rows_avail)
412 my_main_ptr main = (my_main_ptr) cinfo->main;
414 /* Read input data if we haven't filled the main buffer yet */
415 if (! main->buffer_full) {
416 if (! (*cinfo->coef->decompress_data) (cinfo,
417 main->xbuffer[main->whichptr]))
418 return; /* suspension forced, can do nothing more */
419 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
420 main->iMCU_row_ctr++; /* count rows received */
423 /* Postprocessor typically will not swallow all the input data it is handed
424 * in one call (due to filling the output buffer first). Must be prepared
425 * to exit and restart. This switch lets us keep track of how far we got.
426 * Note that each case falls through to the next on successful completion.
428 switch (main->context_state) {
429 case CTX_POSTPONED_ROW:
430 /* Call postprocessor using previously set pointers for postponed row */
431 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
432 &main->rowgroup_ctr, main->rowgroups_avail,
433 output_buf, out_row_ctr, out_rows_avail);
434 if (main->rowgroup_ctr < main->rowgroups_avail)
435 return; /* Need to suspend */
436 main->context_state = CTX_PREPARE_FOR_IMCU;
437 if (*out_row_ctr >= out_rows_avail)
438 return; /* Postprocessor exactly filled output buf */
440 case CTX_PREPARE_FOR_IMCU:
441 /* Prepare to process first M-1 row groups of this iMCU row */
442 main->rowgroup_ctr = 0;
443 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1);
444 /* Check for bottom of image: if so, tweak pointers to "duplicate"
445 * the last sample row, and adjust rowgroups_avail to ignore padding rows.
447 if (main->iMCU_row_ctr == cinfo->total_iMCU_rows)
448 set_bottom_pointers(cinfo);
449 main->context_state = CTX_PROCESS_IMCU;
451 case CTX_PROCESS_IMCU:
452 /* Call postprocessor using previously set pointers */
453 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
454 &main->rowgroup_ctr, main->rowgroups_avail,
455 output_buf, out_row_ctr, out_rows_avail);
456 if (main->rowgroup_ctr < main->rowgroups_avail)
457 return; /* Need to suspend */
458 /* After the first iMCU, change wraparound pointers to normal state */
459 if (main->iMCU_row_ctr == 1)
460 set_wraparound_pointers(cinfo);
461 /* Prepare to load new iMCU row using other xbuffer list */
462 main->whichptr ^= 1; /* 0=>1 or 1=>0 */
463 main->buffer_full = FALSE;
464 /* Still need to process last row group of this iMCU row, */
465 /* which is saved at index M+1 of the other xbuffer */
466 main->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1);
467 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2);
468 main->context_state = CTX_POSTPONED_ROW;
475 * Final pass of two-pass quantization: just call the postprocessor.
476 * Source data will be the postprocessor controller's internal buffer.
479 #ifdef QUANT_2PASS_SUPPORTED
482 process_data_crank_post (j_decompress_ptr cinfo,
483 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
484 JDIMENSION out_rows_avail)
486 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
487 (JDIMENSION *) NULL, (JDIMENSION) 0,
488 output_buf, out_row_ctr, out_rows_avail);
491 #endif /* QUANT_2PASS_SUPPORTED */
495 * Initialize main buffer controller.
499 jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
502 int ci, rgroup, ngroups;
503 jpeg_component_info *compptr;
506 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
507 SIZEOF(my_main_controller));
508 cinfo->main = (struct jpeg_d_main_controller *) main;
509 main->pub.start_pass = start_pass_main;
511 if (need_full_buffer) /* shouldn't happen */
512 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
514 /* Allocate the workspace.
515 * ngroups is the number of row groups we need.
517 if (cinfo->upsample->need_context_rows) {
518 if (cinfo->min_DCT_scaled_size < 2) /* unsupported, see comments above */
519 ERREXIT(cinfo, JERR_NOTIMPL);
520 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
521 ngroups = cinfo->min_DCT_scaled_size + 2;
523 ngroups = cinfo->min_DCT_scaled_size;
526 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
528 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
529 cinfo->min_DCT_scaled_size; /* height of a row group of component */
530 main->buffer[ci] = (*cinfo->mem->alloc_sarray)
531 ((j_common_ptr) cinfo, JPOOL_IMAGE,
532 compptr->width_in_blocks * compptr->DCT_scaled_size,
533 (JDIMENSION) (rgroup * ngroups));