1/*
2 * reserved comment block
3 * DO NOT REMOVE OR ALTER!
4 */
5/*
6 * jdmainct.c
7 *
8 * Copyright (C) 1994-1996, Thomas G. Lane.
9 * This file is part of the Independent JPEG Group's software.
10 * For conditions of distribution and use, see the accompanying README file.
11 *
12 * This file contains the main buffer controller for decompression.
13 * The main buffer lies between the JPEG decompressor proper and the
14 * post-processor; it holds downsampled data in the JPEG colorspace.
15 *
16 * Note that this code is bypassed in raw-data mode, since the application
17 * supplies the equivalent of the main buffer in that case.
18 */
19
20#define JPEG_INTERNALS
21#include "jinclude.h"
22#include "jpeglib.h"
23
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 or
28 * postprocessing controllers. Nonetheless, the main controller is not
29 * trivial. Its responsibility is to provide context rows for upsampling/
30 * rescaling, and doing this in an efficient fashion is a bit tricky.
31 *
32 * Postprocessor input data is counted in "row groups". A row group
33 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
34 * sample rows of each component. (We require DCT_scaled_size values to be
35 * chosen such that these numbers are integers. In practice DCT_scaled_size
36 * values will likely be powers of two, so we actually have the stronger
37 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
38 * Upsampling will typically produce max_v_samp_factor pixel rows from each
39 * row group (times any additional scale factor that the upsampler is
40 * applying).
41 *
42 * The coefficient controller will deliver data to us one iMCU row at a time;
43 * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
44 * exactly min_DCT_scaled_size row groups. (This amount of data corresponds
45 * to one row of MCUs when the image is fully interleaved.) Note that the
46 * number of sample rows varies across components, but the number of row
47 * groups does not. Some garbage sample rows may be included in the last iMCU
48 * row at the bottom of the image.
49 *
50 * Depending on the vertical scaling algorithm used, the upsampler may need
51 * access to the sample row(s) above and below its current input row group.
52 * The upsampler is required to set need_context_rows TRUE at global selection
53 * time if so. When need_context_rows is FALSE, this controller can simply
54 * obtain one iMCU row at a time from the coefficient controller and dole it
55 * out as row groups to the postprocessor.
56 *
57 * When need_context_rows is TRUE, this controller guarantees that the buffer
58 * passed to postprocessing contains at least one row group's worth of samples
59 * above and below the row group(s) being processed. Note that the context
60 * rows "above" the first passed row group appear at negative row offsets in
61 * the passed buffer. At the top and bottom of the image, the required
62 * context rows are manufactured by duplicating the first or last real sample
63 * row; this avoids having special cases in the upsampling inner loops.
64 *
65 * The amount of context is fixed at one row group just because that's a
66 * convenient number for this controller to work with. The existing
67 * upsamplers really only need one sample row of context. An upsampler
68 * supporting arbitrary output rescaling might wish for more than one row
69 * group of context when shrinking the image; tough, we don't handle that.
70 * (This is justified by the assumption that downsizing will be handled mostly
71 * by adjusting the DCT_scaled_size values, so that the actual scale factor at
72 * the upsample step needn't be much less than one.)
73 *
74 * To provide the desired context, we have to retain the last two row groups
75 * of one iMCU row while reading in the next iMCU row. (The last row group
76 * can't be processed until we have another row group for its below-context,
77 * and so we have to save the next-to-last group too for its above-context.)
78 * We could do this most simply by copying data around in our buffer, but
79 * that'd be very slow. We can avoid copying any data by creating a rather
80 * strange pointer structure. Here's how it works. We allocate a workspace
81 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
82 * of row groups per iMCU row). We create two sets of redundant pointers to
83 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
84 * pointer lists look like this:
85 * M+1 M-1
86 * master pointer --> 0 master pointer --> 0
87 * 1 1
88 * ... ...
89 * M-3 M-3
90 * M-2 M
91 * M-1 M+1
92 * M M-2
93 * M+1 M-1
94 * 0 0
95 * We read alternate iMCU rows using each master pointer; thus the last two
96 * row groups of the previous iMCU row remain un-overwritten in the workspace.
97 * The pointer lists are set up so that the required context rows appear to
98 * be adjacent to the proper places when we pass the pointer lists to the
99 * upsampler.
100 *
101 * The above pictures describe the normal state of the pointer lists.
102 * At top and bottom of the image, we diddle the pointer lists to duplicate
103 * the first or last sample row as necessary (this is cheaper than copying
104 * sample rows around).
105 *
106 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
107 * situation each iMCU row provides only one row group so the buffering logic
108 * must be different (eg, we must read two iMCU rows before we can emit the
109 * first row group). For now, we simply do not support providing context
110 * rows when min_DCT_scaled_size is 1. That combination seems unlikely to
111 * be worth providing --- if someone wants a 1/8th-size preview, they probably
112 * want it quick and dirty, so a context-free upsampler is sufficient.
113 */
114
115
116/* Private buffer controller object */
117
118typedef struct {
119 struct jpeg_d_main_controller pub; /* public fields */
120
121 /* Pointer to allocated workspace (M or M+2 row groups). */
122 JSAMPARRAY buffer[MAX_COMPONENTS];
123
124 boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
125 JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
126
127 /* Remaining fields are only used in the context case. */
128
129 /* These are the master pointers to the funny-order pointer lists. */
130 JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
131
132 int whichptr; /* indicates which pointer set is now in use */
133 int context_state; /* process_data state machine status */
134 JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
135 JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */
136} my_main_controller;
137
138typedef my_main_controller * my_main_ptr;
139
140/* context_state values: */
141#define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
142#define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
143#define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
144
145
146/* Forward declarations */
147METHODDEF(void) process_data_simple_main
148 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
149 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
150METHODDEF(void) process_data_context_main
151 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
152 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
153#ifdef QUANT_2PASS_SUPPORTED
154METHODDEF(void) process_data_crank_post
155 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
156 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
157#endif
158
159
160LOCAL(void)
161alloc_funny_pointers (j_decompress_ptr cinfo)
162/* Allocate space for the funny pointer lists.
163 * This is done only once, not once per pass.
164 */
165{
166 my_main_ptr _main = (my_main_ptr) cinfo->main;
167 int ci, rgroup;
168 int M = cinfo->min_DCT_scaled_size;
169 jpeg_component_info *compptr;
170 JSAMPARRAY xbuf;
171
172 /* Get top-level space for component array pointers.
173 * We alloc both arrays with one call to save a few cycles.
174 */
175 _main->xbuffer[0] = (JSAMPIMAGE)
176 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
177 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
178 _main->xbuffer[1] = _main->xbuffer[0] + cinfo->num_components;
179
180 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
181 ci++, compptr++) {
182 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
183 cinfo->min_DCT_scaled_size; /* height of a row group of component */
184 /* Get space for pointer lists --- M+4 row groups in each list.
185 * We alloc both pointer lists with one call to save a few cycles.
186 */
187 xbuf = (JSAMPARRAY)
188 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
189 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
190 xbuf += rgroup; /* want one row group at negative offsets */
191 _main->xbuffer[0][ci] = xbuf;
192 xbuf += rgroup * (M + 4);
193 _main->xbuffer[1][ci] = xbuf;
194 }
195}
196
197
198LOCAL(void)
199make_funny_pointers (j_decompress_ptr cinfo)
200/* Create the funny pointer lists discussed in the comments above.
201 * The actual workspace is already allocated (in main->buffer),
202 * and the space for the pointer lists is allocated too.
203 * This routine just fills in the curiously ordered lists.
204 * This will be repeated at the beginning of each pass.
205 */
206{
207 my_main_ptr _main = (my_main_ptr) cinfo->main;
208 int ci, i, rgroup;
209 int M = cinfo->min_DCT_scaled_size;
210 jpeg_component_info *compptr;
211 JSAMPARRAY buf, xbuf0, xbuf1;
212
213 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
214 ci++, compptr++) {
215 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
216 cinfo->min_DCT_scaled_size; /* height of a row group of component */
217 xbuf0 = _main->xbuffer[0][ci];
218 xbuf1 = _main->xbuffer[1][ci];
219 /* First copy the workspace pointers as-is */
220 buf = _main->buffer[ci];
221 for (i = 0; i < rgroup * (M + 2); i++) {
222 xbuf0[i] = xbuf1[i] = buf[i];
223 }
224 /* In the second list, put the last four row groups in swapped order */
225 for (i = 0; i < rgroup * 2; i++) {
226 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
227 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
228 }
229 /* The wraparound pointers at top and bottom will be filled later
230 * (see set_wraparound_pointers, below). Initially we want the "above"
231 * pointers to duplicate the first actual data line. This only needs
232 * to happen in xbuffer[0].
233 */
234 for (i = 0; i < rgroup; i++) {
235 xbuf0[i - rgroup] = xbuf0[0];
236 }
237 }
238}
239
240
241LOCAL(void)
242set_wraparound_pointers (j_decompress_ptr cinfo)
243/* Set up the "wraparound" pointers at top and bottom of the pointer lists.
244 * This changes the pointer list state from top-of-image to the normal state.
245 */
246{
247 my_main_ptr _main = (my_main_ptr) cinfo->main;
248 int ci, i, rgroup;
249 int M = cinfo->min_DCT_scaled_size;
250 jpeg_component_info *compptr;
251 JSAMPARRAY xbuf0, xbuf1;
252
253 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
254 ci++, compptr++) {
255 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
256 cinfo->min_DCT_scaled_size; /* height of a row group of component */
257 xbuf0 = _main->xbuffer[0][ci];
258 xbuf1 = _main->xbuffer[1][ci];
259 for (i = 0; i < rgroup; i++) {
260 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
261 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
262 xbuf0[rgroup*(M+2) + i] = xbuf0[i];
263 xbuf1[rgroup*(M+2) + i] = xbuf1[i];
264 }
265 }
266}
267
268
269LOCAL(void)
270set_bottom_pointers (j_decompress_ptr cinfo)
271/* Change the pointer lists to duplicate the last sample row at the bottom
272 * of the image. whichptr indicates which xbuffer holds the final iMCU row.
273 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
274 */
275{
276 my_main_ptr _main = (my_main_ptr) cinfo->main;
277 int ci, i, rgroup, iMCUheight, rows_left;
278 jpeg_component_info *compptr;
279 JSAMPARRAY xbuf;
280
281 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
282 ci++, compptr++) {
283 /* Count sample rows in one iMCU row and in one row group */
284 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size;
285 rgroup = iMCUheight / cinfo->min_DCT_scaled_size;
286 /* Count nondummy sample rows remaining for this component */
287 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
288 if (rows_left == 0) rows_left = iMCUheight;
289 /* Count nondummy row groups. Should get same answer for each component,
290 * so we need only do it once.
291 */
292 if (ci == 0) {
293 _main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
294 }
295 /* Duplicate the last real sample row rgroup*2 times; this pads out the
296 * last partial rowgroup and ensures at least one full rowgroup of context.
297 */
298 xbuf = _main->xbuffer[_main->whichptr][ci];
299 for (i = 0; i < rgroup * 2; i++) {
300 xbuf[rows_left + i] = xbuf[rows_left-1];
301 }
302 }
303}
304
305
306/*
307 * Initialize for a processing pass.
308 */
309
310METHODDEF(void)
311start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
312{
313 my_main_ptr _main = (my_main_ptr) cinfo->main;
314
315 switch (pass_mode) {
316 case JBUF_PASS_THRU:
317 if (cinfo->upsample->need_context_rows) {
318 _main->pub.process_data = process_data_context_main;
319 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
320 _main->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
321 _main->context_state = CTX_PREPARE_FOR_IMCU;
322 _main->iMCU_row_ctr = 0;
323 } else {
324 /* Simple case with no context needed */
325 _main->pub.process_data = process_data_simple_main;
326 }
327 _main->buffer_full = FALSE; /* Mark buffer empty */
328 _main->rowgroup_ctr = 0;
329 break;
330#ifdef QUANT_2PASS_SUPPORTED
331 case JBUF_CRANK_DEST:
332 /* For last pass of 2-pass quantization, just crank the postprocessor */
333 _main->pub.process_data = process_data_crank_post;
334 break;
335#endif
336 default:
337 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
338 break;
339 }
340}
341
342
343/*
344 * Process some data.
345 * This handles the simple case where no context is required.
346 */
347
348METHODDEF(void)
349process_data_simple_main (j_decompress_ptr cinfo,
350 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
351 JDIMENSION out_rows_avail)
352{
353 my_main_ptr _main = (my_main_ptr) cinfo->main;
354 JDIMENSION rowgroups_avail;
355
356 /* Read input data if we haven't filled the main buffer yet */
357 if (! _main->buffer_full) {
358 if (! (*cinfo->coef->decompress_data) (cinfo, _main->buffer))
359 return; /* suspension forced, can do nothing more */
360 _main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
361 }
362
363 /* There are always min_DCT_scaled_size row groups in an iMCU row. */
364 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size;
365 /* Note: at the bottom of the image, we may pass extra garbage row groups
366 * to the postprocessor. The postprocessor has to check for bottom
367 * of image anyway (at row resolution), so no point in us doing it too.
368 */
369
370 /* Feed the postprocessor */
371 (*cinfo->post->post_process_data) (cinfo, _main->buffer,
372 &_main->rowgroup_ctr, rowgroups_avail,
373 output_buf, out_row_ctr, out_rows_avail);
374
375 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
376 if (_main->rowgroup_ctr >= rowgroups_avail) {
377 _main->buffer_full = FALSE;
378 _main->rowgroup_ctr = 0;
379 }
380}
381
382
383/*
384 * Process some data.
385 * This handles the case where context rows must be provided.
386 */
387
388METHODDEF(void)
389process_data_context_main (j_decompress_ptr cinfo,
390 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
391 JDIMENSION out_rows_avail)
392{
393 my_main_ptr _main = (my_main_ptr) cinfo->main;
394
395 /* Read input data if we haven't filled the _main buffer yet */
396 if (! _main->buffer_full) {
397 if (! (*cinfo->coef->decompress_data) (cinfo,
398 _main->xbuffer[_main->whichptr]))
399 return; /* suspension forced, can do nothing more */
400 _main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
401 _main->iMCU_row_ctr++; /* count rows received */
402 }
403
404 /* Postprocessor typically will not swallow all the input data it is handed
405 * in one call (due to filling the output buffer first). Must be prepared
406 * to exit and restart. This switch lets us keep track of how far we got.
407 * Note that each case falls through to the next on successful completion.
408 */
409 switch (_main->context_state) {
410 case CTX_POSTPONED_ROW:
411 /* Call postprocessor using previously set pointers for postponed row */
412 (*cinfo->post->post_process_data) (cinfo, _main->xbuffer[_main->whichptr],
413 &_main->rowgroup_ctr, _main->rowgroups_avail,
414 output_buf, out_row_ctr, out_rows_avail);
415 if (_main->rowgroup_ctr < _main->rowgroups_avail)
416 return; /* Need to suspend */
417 _main->context_state = CTX_PREPARE_FOR_IMCU;
418 if (*out_row_ctr >= out_rows_avail)
419 return; /* Postprocessor exactly filled output buf */
420 /*FALLTHROUGH*/
421 case CTX_PREPARE_FOR_IMCU:
422 /* Prepare to process first M-1 row groups of this iMCU row */
423 _main->rowgroup_ctr = 0;
424 _main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1);
425 /* Check for bottom of image: if so, tweak pointers to "duplicate"
426 * the last sample row, and adjust rowgroups_avail to ignore padding rows.
427 */
428 if (_main->iMCU_row_ctr == cinfo->total_iMCU_rows)
429 set_bottom_pointers(cinfo);
430 _main->context_state = CTX_PROCESS_IMCU;
431 /*FALLTHROUGH*/
432 case CTX_PROCESS_IMCU:
433 /* Call postprocessor using previously set pointers */
434 (*cinfo->post->post_process_data) (cinfo, _main->xbuffer[_main->whichptr],
435 &_main->rowgroup_ctr, _main->rowgroups_avail,
436 output_buf, out_row_ctr, out_rows_avail);
437 if (_main->rowgroup_ctr < _main->rowgroups_avail)
438 return; /* Need to suspend */
439 /* After the first iMCU, change wraparound pointers to normal state */
440 if (_main->iMCU_row_ctr == 1)
441 set_wraparound_pointers(cinfo);
442 /* Prepare to load new iMCU row using other xbuffer list */
443 _main->whichptr ^= 1; /* 0=>1 or 1=>0 */
444 _main->buffer_full = FALSE;
445 /* Still need to process last row group of this iMCU row, */
446 /* which is saved at index M+1 of the other xbuffer */
447 _main->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1);
448 _main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2);
449 _main->context_state = CTX_POSTPONED_ROW;
450 }
451}
452
453
454/*
455 * Process some data.
456 * Final pass of two-pass quantization: just call the postprocessor.
457 * Source data will be the postprocessor controller's internal buffer.
458 */
459
460#ifdef QUANT_2PASS_SUPPORTED
461
462METHODDEF(void)
463process_data_crank_post (j_decompress_ptr cinfo,
464 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
465 JDIMENSION out_rows_avail)
466{
467 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
468 (JDIMENSION *) NULL, (JDIMENSION) 0,
469 output_buf, out_row_ctr, out_rows_avail);
470}
471
472#endif /* QUANT_2PASS_SUPPORTED */
473
474
475/*
476 * Initialize main buffer controller.
477 */
478
479GLOBAL(void)
480jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
481{
482 my_main_ptr _main;
483 int ci, rgroup, ngroups;
484 jpeg_component_info *compptr;
485
486 _main = (my_main_ptr)
487 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
488 SIZEOF(my_main_controller));
489 cinfo->main = (struct jpeg_d_main_controller *) _main;
490 _main->pub.start_pass = start_pass_main;
491
492 if (need_full_buffer) /* shouldn't happen */
493 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
494
495 /* Allocate the workspace.
496 * ngroups is the number of row groups we need.
497 */
498 if (cinfo->upsample->need_context_rows) {
499 if (cinfo->min_DCT_scaled_size < 2) /* unsupported, see comments above */
500 ERREXIT(cinfo, JERR_NOTIMPL);
501 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
502 ngroups = cinfo->min_DCT_scaled_size + 2;
503 } else {
504 ngroups = cinfo->min_DCT_scaled_size;
505 }
506
507 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
508 ci++, compptr++) {
509 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
510 cinfo->min_DCT_scaled_size; /* height of a row group of component */
511 _main->buffer[ci] = (*cinfo->mem->alloc_sarray)
512 ((j_common_ptr) cinfo, JPOOL_IMAGE,
513 compptr->width_in_blocks * compptr->DCT_scaled_size,
514 (JDIMENSION) (rgroup * ngroups));
515 }
516}
517