7 * Copyright (C) 1994-1995, Thomas G. Lane.
9 * This file is part of the Independent JPEG Group's software.
11 * For conditions of distribution and use, see the accompanying README file.
15 * This file contains the main buffer controller for decompression.
17 * The main buffer lies between the JPEG decompressor proper and the
19 * post-processor; it holds downsampled data in the JPEG colorspace.
23 * Note that this code is bypassed in raw-data mode, since the application
25 * supplies the equivalent of the main buffer in that case.
31 #define JPEG_INTERNALS
35 #include "radiant_jpeglib.h"
43 * In the current system design, the main buffer need never be a full-image
45 * buffer; any full-height buffers will be found inside the coefficient or
47 * postprocessing controllers. Nonetheless, the main controller is not
49 * trivial. Its responsibility is to provide context rows for upsampling/
51 * rescaling, and doing this in an efficient fashion is a bit tricky.
55 * Postprocessor input data is counted in "row groups". A row group
57 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
59 * sample rows of each component. (We require DCT_scaled_size values to be
61 * chosen such that these numbers are integers. In practice DCT_scaled_size
63 * values will likely be powers of two, so we actually have the stronger
65 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
67 * Upsampling will typically produce max_v_samp_factor pixel rows from each
69 * row group (times any additional scale factor that the upsampler is
75 * The coefficient controller will deliver data to us one iMCU row at a time;
77 * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
79 * exactly min_DCT_scaled_size row groups. (This amount of data corresponds
81 * to one row of MCUs when the image is fully interleaved.) Note that the
83 * number of sample rows varies across components, but the number of row
85 * groups does not. Some garbage sample rows may be included in the last iMCU
87 * row at the bottom of the image.
91 * Depending on the vertical scaling algorithm used, the upsampler may need
93 * access to the sample row(s) above and below its current input row group.
95 * The upsampler is required to set need_context_rows TRUE at global selection
97 * time if so. When need_context_rows is FALSE, this controller can simply
99 * obtain one iMCU row at a time from the coefficient controller and dole it
101 * out as row groups to the postprocessor.
105 * When need_context_rows is TRUE, this controller guarantees that the buffer
107 * passed to postprocessing contains at least one row group's worth of samples
109 * above and below the row group(s) being processed. Note that the context
111 * rows "above" the first passed row group appear at negative row offsets in
113 * the passed buffer. At the top and bottom of the image, the required
115 * context rows are manufactured by duplicating the first or last real sample
117 * row; this avoids having special cases in the upsampling inner loops.
121 * The amount of context is fixed at one row group just because that's a
123 * convenient number for this controller to work with. The existing
125 * upsamplers really only need one sample row of context. An upsampler
127 * supporting arbitrary output rescaling might wish for more than one row
129 * group of context when shrinking the image; tough, we don't handle that.
131 * (This is justified by the assumption that downsizing will be handled mostly
133 * by adjusting the DCT_scaled_size values, so that the actual scale factor at
135 * the upsample step needn't be much less than one.)
139 * To provide the desired context, we have to retain the last two row groups
141 * of one iMCU row while reading in the next iMCU row. (The last row group
143 * can't be processed until we have another row group for its below-context,
145 * and so we have to save the next-to-last group too for its above-context.)
147 * We could do this most simply by copying data around in our buffer, but
149 * that'd be very slow. We can avoid copying any data by creating a rather
151 * strange pointer structure. Here's how it works. We allocate a workspace
153 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
155 * of row groups per iMCU row). We create two sets of redundant pointers to
157 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
159 * pointer lists look like this:
163 * master pointer --> 0 master pointer --> 0
181 * We read alternate iMCU rows using each master pointer; thus the last two
183 * row groups of the previous iMCU row remain un-overwritten in the workspace.
185 * The pointer lists are set up so that the required context rows appear to
187 * be adjacent to the proper places when we pass the pointer lists to the
193 * The above pictures describe the normal state of the pointer lists.
195 * At top and bottom of the image, we diddle the pointer lists to duplicate
197 * the first or last sample row as necessary (this is cheaper than copying
199 * sample rows around).
203 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
205 * situation each iMCU row provides only one row group so the buffering logic
207 * must be different (eg, we must read two iMCU rows before we can emit the
209 * first row group). For now, we simply do not support providing context
211 * rows when min_DCT_scaled_size is 1. That combination seems unlikely to
213 * be worth providing --- if someone wants a 1/8th-size preview, they probably
215 * want it quick and dirty, so a context-free upsampler is sufficient.
223 /* Private buffer controller object */
229 struct jpeg_d_main_controller pub; /* public fields */
233 /* Pointer to allocated workspace (M or M+2 row groups). */
235 JSAMPARRAY buffer[MAX_COMPONENTS];
239 boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
241 JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
245 /* Remaining fields are only used in the context case. */
249 /* These are the master pointers to the funny-order pointer lists. */
251 JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
255 int whichptr; /* indicates which pointer set is now in use */
257 int context_state; /* process_data state machine status */
259 JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
261 JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */
263 } my_main_controller;
267 typedef my_main_controller * my_main_ptr;
271 /* context_state values: */
273 #define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
275 #define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
277 #define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
283 /* Forward declarations */
285 METHODDEF void process_data_simple_main
287 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
289 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
291 METHODDEF void process_data_context_main
293 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
295 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
297 #ifdef QUANT_2PASS_SUPPORTED
299 METHODDEF void process_data_crank_post
301 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
303 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
313 alloc_funny_pointers (j_decompress_ptr cinfo)
315 /* Allocate space for the funny pointer lists.
317 * This is done only once, not once per pass.
323 my_main_ptr main = (my_main_ptr) cinfo->main;
327 int M = cinfo->min_DCT_scaled_size;
329 jpeg_component_info *compptr;
335 /* Get top-level space for component array pointers.
337 * We alloc both arrays with one call to save a few cycles.
341 main->xbuffer[0] = (JSAMPIMAGE)
343 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
345 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
347 main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components;
351 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
355 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
357 cinfo->min_DCT_scaled_size; /* height of a row group of component */
359 /* Get space for pointer lists --- M+4 row groups in each list.
361 * We alloc both pointer lists with one call to save a few cycles.
367 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
369 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
371 xbuf += rgroup; /* want one row group at negative offsets */
373 main->xbuffer[0][ci] = xbuf;
375 xbuf += rgroup * (M + 4);
377 main->xbuffer[1][ci] = xbuf;
389 make_funny_pointers (j_decompress_ptr cinfo)
391 /* Create the funny pointer lists discussed in the comments above.
393 * The actual workspace is already allocated (in main->buffer),
395 * and the space for the pointer lists is allocated too.
397 * This routine just fills in the curiously ordered lists.
399 * This will be repeated at the beginning of each pass.
405 my_main_ptr main = (my_main_ptr) cinfo->main;
409 int M = cinfo->min_DCT_scaled_size;
411 jpeg_component_info *compptr;
413 JSAMPARRAY buf, xbuf0, xbuf1;
417 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
421 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
423 cinfo->min_DCT_scaled_size; /* height of a row group of component */
425 xbuf0 = main->xbuffer[0][ci];
427 xbuf1 = main->xbuffer[1][ci];
429 /* First copy the workspace pointers as-is */
431 buf = main->buffer[ci];
433 for (i = 0; i < rgroup * (M + 2); i++) {
435 xbuf0[i] = xbuf1[i] = buf[i];
439 /* In the second list, put the last four row groups in swapped order */
441 for (i = 0; i < rgroup * 2; i++) {
443 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
445 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
449 /* The wraparound pointers at top and bottom will be filled later
451 * (see set_wraparound_pointers, below). Initially we want the "above"
453 * pointers to duplicate the first actual data line. This only needs
455 * to happen in xbuffer[0].
459 for (i = 0; i < rgroup; i++) {
461 xbuf0[i - rgroup] = xbuf0[0];
475 set_wraparound_pointers (j_decompress_ptr cinfo)
477 /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
479 * This changes the pointer list state from top-of-image to the normal state.
485 my_main_ptr main = (my_main_ptr) cinfo->main;
489 int M = cinfo->min_DCT_scaled_size;
491 jpeg_component_info *compptr;
493 JSAMPARRAY xbuf0, xbuf1;
497 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
501 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
503 cinfo->min_DCT_scaled_size; /* height of a row group of component */
505 xbuf0 = main->xbuffer[0][ci];
507 xbuf1 = main->xbuffer[1][ci];
509 for (i = 0; i < rgroup; i++) {
511 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
513 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
515 xbuf0[rgroup*(M+2) + i] = xbuf0[i];
517 xbuf1[rgroup*(M+2) + i] = xbuf1[i];
531 set_bottom_pointers (j_decompress_ptr cinfo)
533 /* Change the pointer lists to duplicate the last sample row at the bottom
535 * of the image. whichptr indicates which xbuffer holds the final iMCU row.
537 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
543 my_main_ptr main = (my_main_ptr) cinfo->main;
545 int ci, i, rgroup, iMCUheight, rows_left;
547 jpeg_component_info *compptr;
553 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
557 /* Count sample rows in one iMCU row and in one row group */
559 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size;
561 rgroup = iMCUheight / cinfo->min_DCT_scaled_size;
563 /* Count nondummy sample rows remaining for this component */
565 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
567 if (rows_left == 0) rows_left = iMCUheight;
569 /* Count nondummy row groups. Should get same answer for each component,
571 * so we need only do it once.
577 main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
581 /* Duplicate the last real sample row rgroup*2 times; this pads out the
583 * last partial rowgroup and ensures at least one full rowgroup of context.
587 xbuf = main->xbuffer[main->whichptr][ci];
589 for (i = 0; i < rgroup * 2; i++) {
591 xbuf[rows_left + i] = xbuf[rows_left-1];
605 * Initialize for a processing pass.
613 start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
617 my_main_ptr main = (my_main_ptr) cinfo->main;
625 if (cinfo->upsample->need_context_rows) {
627 main->pub.process_data = process_data_context_main;
629 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
631 main->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
633 main->context_state = CTX_PREPARE_FOR_IMCU;
635 main->iMCU_row_ctr = 0;
639 /* Simple case with no context needed */
641 main->pub.process_data = process_data_simple_main;
645 main->buffer_full = FALSE; /* Mark buffer empty */
647 main->rowgroup_ctr = 0;
651 #ifdef QUANT_2PASS_SUPPORTED
653 case JBUF_CRANK_DEST:
655 /* For last pass of 2-pass quantization, just crank the postprocessor */
657 main->pub.process_data = process_data_crank_post;
665 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
681 * This handles the simple case where no context is required.
689 process_data_simple_main (j_decompress_ptr cinfo,
691 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
693 JDIMENSION out_rows_avail)
697 my_main_ptr main = (my_main_ptr) cinfo->main;
699 JDIMENSION rowgroups_avail;
703 /* Read input data if we haven't filled the main buffer yet */
705 if (! main->buffer_full) {
707 if (! (*cinfo->coef->decompress_data) (cinfo, main->buffer))
709 return; /* suspension forced, can do nothing more */
711 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
717 /* There are always min_DCT_scaled_size row groups in an iMCU row. */
719 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size;
721 /* Note: at the bottom of the image, we may pass extra garbage row groups
723 * to the postprocessor. The postprocessor has to check for bottom
725 * of image anyway (at row resolution), so no point in us doing it too.
731 /* Feed the postprocessor */
733 (*cinfo->post->post_process_data) (cinfo, main->buffer,
735 &main->rowgroup_ctr, rowgroups_avail,
737 output_buf, out_row_ctr, out_rows_avail);
741 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
743 if (main->rowgroup_ctr >= rowgroups_avail) {
745 main->buffer_full = FALSE;
747 main->rowgroup_ctr = 0;
761 * This handles the case where context rows must be provided.
769 process_data_context_main (j_decompress_ptr cinfo,
771 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
773 JDIMENSION out_rows_avail)
777 my_main_ptr main = (my_main_ptr) cinfo->main;
781 /* Read input data if we haven't filled the main buffer yet */
783 if (! main->buffer_full) {
785 if (! (*cinfo->coef->decompress_data) (cinfo,
787 main->xbuffer[main->whichptr]))
789 return; /* suspension forced, can do nothing more */
791 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
793 main->iMCU_row_ctr++; /* count rows received */
799 /* Postprocessor typically will not swallow all the input data it is handed
801 * in one call (due to filling the output buffer first). Must be prepared
803 * to exit and restart. This switch lets us keep track of how far we got.
805 * Note that each case falls through to the next on successful completion.
809 switch (main->context_state) {
811 case CTX_POSTPONED_ROW:
813 /* Call postprocessor using previously set pointers for postponed row */
815 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
817 &main->rowgroup_ctr, main->rowgroups_avail,
819 output_buf, out_row_ctr, out_rows_avail);
821 if (main->rowgroup_ctr < main->rowgroups_avail)
823 return; /* Need to suspend */
825 main->context_state = CTX_PREPARE_FOR_IMCU;
827 if (*out_row_ctr >= out_rows_avail)
829 return; /* Postprocessor exactly filled output buf */
833 case CTX_PREPARE_FOR_IMCU:
835 /* Prepare to process first M-1 row groups of this iMCU row */
837 main->rowgroup_ctr = 0;
839 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1);
841 /* Check for bottom of image: if so, tweak pointers to "duplicate"
843 * the last sample row, and adjust rowgroups_avail to ignore padding rows.
847 if (main->iMCU_row_ctr == cinfo->total_iMCU_rows)
849 set_bottom_pointers(cinfo);
851 main->context_state = CTX_PROCESS_IMCU;
855 case CTX_PROCESS_IMCU:
857 /* Call postprocessor using previously set pointers */
859 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
861 &main->rowgroup_ctr, main->rowgroups_avail,
863 output_buf, out_row_ctr, out_rows_avail);
865 if (main->rowgroup_ctr < main->rowgroups_avail)
867 return; /* Need to suspend */
869 /* After the first iMCU, change wraparound pointers to normal state */
871 if (main->iMCU_row_ctr == 1)
873 set_wraparound_pointers(cinfo);
875 /* Prepare to load new iMCU row using other xbuffer list */
877 main->whichptr ^= 1; /* 0=>1 or 1=>0 */
879 main->buffer_full = FALSE;
881 /* Still need to process last row group of this iMCU row, */
883 /* which is saved at index M+1 of the other xbuffer */
885 main->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1);
887 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2);
889 main->context_state = CTX_POSTPONED_ROW;
903 * Final pass of two-pass quantization: just call the postprocessor.
905 * Source data will be the postprocessor controller's internal buffer.
911 #ifdef QUANT_2PASS_SUPPORTED
917 process_data_crank_post (j_decompress_ptr cinfo,
919 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
921 JDIMENSION out_rows_avail)
925 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
927 (JDIMENSION *) NULL, (JDIMENSION) 0,
929 output_buf, out_row_ctr, out_rows_avail);
935 #endif /* QUANT_2PASS_SUPPORTED */
943 * Initialize main buffer controller.
951 jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
957 int ci, rgroup, ngroups;
959 jpeg_component_info *compptr;
965 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
967 SIZEOF(my_main_controller));
969 cinfo->main = (struct jpeg_d_main_controller *) main;
971 main->pub.start_pass = start_pass_main;
975 if (need_full_buffer) /* shouldn't happen */
977 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
981 /* Allocate the workspace.
983 * ngroups is the number of row groups we need.
987 if (cinfo->upsample->need_context_rows) {
989 if (cinfo->min_DCT_scaled_size < 2) /* unsupported, see comments above */
991 ERREXIT(cinfo, JERR_NOTIMPL);
993 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
995 ngroups = cinfo->min_DCT_scaled_size + 2;
999 ngroups = cinfo->min_DCT_scaled_size;
1005 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
1009 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
1011 cinfo->min_DCT_scaled_size; /* height of a row group of component */
1013 main->buffer[ci] = (*cinfo->mem->alloc_sarray)
1015 ((j_common_ptr) cinfo, JPOOL_IMAGE,
1017 compptr->width_in_blocks * compptr->DCT_scaled_size,
1019 (JDIMENSION) (rgroup * ngroups));